9. APPENDIX B - TOLERANCES FOR HOT UPSET FORGINGS

GUIDELINE TOLERANCES FOR HOT UPSET FORGINGS

INTRODUCTION

Fundamentally, impression die forgings produced on Horizontal Forging Machines (Upsetters) are similar to those produced by Hammers or Presses. Each is the result of forcing metal into cavities in dies which separate at parting lines.

The impression in the ram-operated "Heading Tool" is the equivalent of a Hammer or Press top die. The "grip dies" contain the impressions corresponding to the Hammer or Press bottom die. Grip dies consist of a stationary die and a moving die which, when closed, act to grip the stock and hold it in position for forging. After each workstroke of the machine, these dies open to permit the transfer of stock from one cavity to another in the multiple-impression dies.

After an operation establishes a final contour on a specific portion of an upset forging, subsequent operations may have some effect on that portion. Thus the number and sequence of steps used in shaping the forging must be planned in advance in order that overall tolerance may be anticipated.

Most upset forgings begin with and retain some portion of a hot rolled bar. Permissible mill variations thus have an effect on upset forging tolerances.

As a result of this and other technical considerations, tolerances applying to forgings produced on Forging Machines differ somewhat from those of Hammer and Press forgings.

TOLERANCES

There are practical limitations in dimensions and other characteristics of forged parts or products which vary according to the part or product and the producer's equipment. The degree of precision practicable in the manufacture of forged parts or products is dictated by the essential character of forging equipment and unavoidable contingencies in forging operations.

Theoretical exactness is seldom attained, and it is therefore necessary to make allowances for deviations. The tolerances set forth herein represent what the Forging Industry Association believes to be typical within the industry, as determined by actual measurements of forgings produced under normal operating conditions on standard forging equipment.

Experience within the industry shows that dimensional variations in forging are commonly functions of the dimensions involved, and the tolerances herein are based upon this observed fact.

TOLERANCE ACCUMULATION

Where applicable the enclosed tolerances are accumulative. (Example: overall length tolerance = flange thickness tolerance + stem length tolerance.)

The experience of producers and purchasers of forged parts and products indicates that the tolerances set forth herein will provide adequate dimensional accuracy for most applications.

THE TOLERANCES OUTLINED IN THIS BOOKLET ARE GUIDELINES BASED ON HISTORICAL, AVERAGED DATA. THE TERMS OF EACH TRANSACTION BETWEEN A FORGING PRODUCER AND A PURCHASER, INCLUDING TOLERANCES APPLICABLE TO THAT TRANSACTION, MUST BE NEGOTIATED AND CONFIRMED IN ADVANCE OF PRODUCTION.

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GENERAL

All individual tolerances apply to each and every forged part unless specifically noted otherwise.

Tolerances as stated in all tables are considered for use by final inspection departments at the forge plant and/or by receiving or source inspection by the purchaser.

PRINTS AND SPECIFICATIONS

It is important that forging drawings be accurate and complete. The purchaser should indicate his first operation locating points, normally as a part of the drawing, and give prior notice should these points be changed.
 
It is equally important that the purchaser provide drawings of the finish machined part, or equivalent information. This will assist in the design of forging dies and tools, and in establishing most effective final inspection procedures.
Unless the purchaser's drawings and specifications direct otherwise, all dimensions are normally assumed to refer to lines intersecting at right angles to each other (commonly referred to as X,, Y, and Z axes). Furthermore, unless the purchaser's drawings or specifications direct otherwise, circular shapes are normally assumed to be figures of revolution with a center on an axis, and all circular dimensions are normally shown as diameters.
 
DIMENSIONAL PRACTICES FOR FORGING DRAWINGS
 
At the time of first printing of this publication, a transition period existed dealing with the conversion from the customary decimal inch system to dimensioning to the metric system. The following procedures will apply concerning dimensioning on forging drawings: (1) Metric System _ metric dimensions, on forging drawings, will be extended to one place decimal millimeter for both part dimensions and tolerances (0.1); and (2) Decimal Inch System _ inch units of measure on forging drawings will be extended to two place decimals for both dimensions and tolerances (0.01).
UNITS AND METHODS OF MEASURE METHOD
The forgeman must do much of his measuring (hot inspection) of forgings while they are hot, using practical forge shop instruments such as calipers, rule, straight edge and profile template. The precision of his measurements is therefore limited by the characteristics of such instruments and the conditions under which they must be used.

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UNIT OF MEASURE
Tolerances in this publication are expressed in decimal inch with metric equivalents in the belief that this represents practice most common in the industry at the time of publication.
NOTE: THESE ARE GUIDELINES BASED ON AVERAGES IN THE FORGING INDUSTRY. REFINEMENTS TO THE ENCLOSED TOLERANCES CAN BE MADE IN RELATIONSHIP TO SMALLER DRAFT ANGLES, TIGHTER SQUARENESS, ROUNDNESS, PARALLELISM, STEP DESIGNS AND STRAIGHTNESS. OPERATIONS CAN BE PERFORMED BY FORGE PLANTS TO PROVIDE ADDITIONAL SERVICES WHICH IN MANY CASES REPLACE THE NEED FOR MACHINING.
FLANGE THICKNESS TOLERANCES (Heading Tool Closure)
SCOPE
1. (a) Flange Thickness Tolerances reflect the degree of closure of the heading tool. When more than one flange is formed, these tolerances also apply to the dimension (gap) between flanges.
  (b) Flange Thickness Tolerances are applied separately and independently of other tolerances and are accumulative.
TOLERANCE
2. (a) Tolerances for flange thickness and dimensions (gaps) between flanges are such that the effect is to add stock on both internal and external dimensions. The amount of Flange Thickness Tolerance depends on the flange diameter.
  (b) When two flanges are formed, the tolerance on the dimension (gap) between them is a minus tolerance only, with a value identical to the thickness tolerance for the flange nearest the unforged stem. (See Figure 15)
  (c) Flange Thickness Tolerances are shown in Table VII and Figure 15.
MEASURING FOR FLANGE THICKNESS TOLERANCE
3.   Flange Thickness Tolerance depends on the flange diameter.
UNITS OF MEASURE
4.    Flange Thickness Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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METRIC CONVERSION
INCH mm
0.06 1.5
0.09 2.3
1.25 31.8
1.50 38.1
3.75 95.3
7.00 177.8
8.00 203.2

TABLE VIII
FLANGE THICKNESS TOLERANCES

METRIC Diameters TOLERANCES    
Over But Not Over Plus Minus    
0 180 1.6 --    
180.0 255.0 2.3 --    
255.0 -- 3.4 0.8    

 

INCH Diameters TOLERANCES    
Over But Not Over Plus Minus    
0 7.00 0.06 --    
7.00 10.00 0.09 --    
10.00 -- 0.13 0.03    

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STEM TOLERANCES

SCOPE

1.   Stem Tolerances relate to that portion of the forging from the first flange (flange nearest the unforged end) to the unforged end.

TOLERANCE

2. (a) Stem Tolerances are based on stem length and are expressed as decimals of an inch or mm according to Table IX.
  (b) The diameter of the unheated stem is controlled by mill tolerances. The stem length subjected to forging heat is covered by diameter tolerance (Table XI). The portion of the "heated stem" will vary due to the equipment, process and part geometry. Agreement between the forging producer and forging purchaser should be reached prior to acceptance of order.

MEASURING FOR STEM LENGTH TOLERANCE

3.   Stem Length Tolerances are measured parallel to the axis of the stock from the first flange to the unforged end.
  (b) The diameter of the unheated stem is controlled by mill tolerances. The stem length subjected to forging heat is covered by diameter tolerance (Table XI). The portion of the "heated stem" will vary due to the equipment, process and part geometry. Agreement between the forging producer and forging purchaser should be reached prior to acceptance of order.
 

NOTE:

Line AA, Figure 16 denotes first portion of the forging controlled by the Flange Thickness Tolerance.

UNITS OF MEASURE

4.   Stem Length Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch, in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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METRIC CONVERSION
INCH mm
0.06 1.6
0.09 2.3
0.13 3.4
3.50 88.9
3.75 95.3
10.75 273.1
18.00 457.2

 

TABLE IX
STEM TOLERANCES

METRIC Stem Length TOLERANCES
Over But Not Over Plus Minus
0.0 152.4 1.6 0.08
152.0 254.0 2.3 .8
254.0 508.0 3.4 01.6
508.0 762.0 4.0 1.6
762.0 -- As Agreed --

 

INCH Stem Length TOLERANCES
Over But Not Over Plus Minus
0.00 6.00 0.06 0.03
6.00 10.00 0.09 0.03
10.00 20.00 0.13 0.06
20.00 30.00 0.19 0.06
30.00 -- As Agreed --

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SHOULDER LENGTH TOLERANCES

SCOPE
  1.    Shoulder Length Tolerances apply to portions of the final forging formed as steps to or from a flange and not affected by header closure. Tolerances on the flange thickness, internal length (gap) dimension between flanges and the unforged portion of the stem are toleranced separately and independently of the Shoulder Length Tolerances. Shoulder Length Tolerances include allowances for die wear, shrinkage, die sinking and die polishing variations.
TOLERANCE
   2.Shoulder Length Tolerances are plus values only, expressed in decimals of an inch or mm according to Table X.
MEASURING FOR SHOULDER LENGTH TOLERANCE
   3. Shoulder Length Tolerances are measured parallel to the axis of the original bar.
UNITS OF MEASURE  
4. Shoulder Length Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch, in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next    highest 0.1 in the metric system or 0.01 in the inch system.

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METRIC CONVERSION
INCH mm
0.06 1.6
0.09 2.3
1.00 25.4
1.13 28.8
1.50 38.1
1.75 44.5
3.50 88.9

TABLE X
SHOULDER LENGTH TOLERANCES

METRIC Length Dimensions TOLERANCES
Over But Not Over  
-- 76.2 1.6
76.2 152.4 2.3
152.4 228.6 3.4
228.6 -- 4.1

 

INCH Length Dimensions TOLERANCES
Over But Not Over  
-- 3.00 0.06
3.00 6.00 0.09
6.00 9.00 0.13
9.00 -- 0.16
 

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DIAMETER TOLERANCES

SCOPE
1. (a)Diameter Tolerances are applied separately for each of a forging's diameters and only to those diameters formed in the heading tool or dies.
    (b)These tolerances apply only to forgings with circular shape. Tolerances for non-circular forgings are customarily determined by special agreement between purchaser and producer in advance of production.

TOLERANCE
2. (a)Tolerances for all external forged diameters are expressed as plus tolerances only, according to Table XI.
    (b)Tolerances for internal diameters of holes formed by the heading tool are commonly expressed as minus tolerances only according to Table XI.
    (c)Tolerances for Stem Diameters subjected to forging heat are shown in Table XI. Variations in diameter on unheated portions of the stem are commonly governed by mill tolerances.
    (d)Tolerance for shear-cut ends and slight irregularities in diameter on the stem caused by grip dies are commonly determined by special agreement between purchaser and producer.

MEASURING FOR DIAMETER TOLERANCES
3. Diameter Tolerances are commonly applied and measured in a plane 90° from the die parting line (perpendicular to the axis of the stock).

UNITS OF MEASURE
4. Diameter Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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METRIC CONVERSION
INCH mm
0.06 1.6
0.09 2.3
3.50 88.9
3.56 90.5
4.25 108.0
5.00 127.0
6.75 171.5
6.75 203.2

TABLE XI
DIAMETER TOLERANT

METRIC Diameters TOLERANT
Over But Not Over Outside Diameters Inside Diameter
-- 50.8 + 0.8 - 1.6
50.8 177.8 + 1.6 - 2.3
177.8 254.0 + 2.3 - 3.4
254.0 -- + 3.4 - 3.4

 

INCH Diameters TOLERANT
Over But Not Over Outside Diameters Inside Diameter
-- 2.00 + 0.03 - 0.06
2.00 7.00 + 0.06 - 0.09
7.00 10.00 + 0.09 - 0.13
10.00 -- + 0.13 - 0.13
 

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GRIP DIES TOLERANCES

SCOPE
1. Grip Dies Match Tolerances relate to the amount of die displacement in a direction parallel to the parting line of the grip dies. Grip Dies Match describes the results of movement of one die in relation to the other. While this movement is along the die parting line only, it does occur in two ways. Vertical Shift: Where one die is higher than the other. Forward Shift: Where one die is ahead of the other.
TOLERANCE
2. Grip Dies Match Tolerances are based on the largest forging diameter and shown in Table XII. These tolerances are applied independently of and in addition to all other tolerances.
MEASURING FOR SHOULDER LENGTH TOLERANCE
3. Vertical Shift is determined by measuring the difference between AA and BB then dividing by two. (See Fig. 19A.)
Forward Shift is determined by measuring the difference between DD and EE. (See Figure 19B.)
In cases where measurements for determining match tolerances must be made from surfaces of the forging where uneven wearing of the dies has caused surplus stock, accuracy depends on making the proper allowances for these wear-caused surpluses, and eliminating their influence from the computation.
UNITS OF MEASURE
4. Grip Dies Match Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch, in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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TABLE XXII
GRIP DIES MATCH TOLERANCE

METRIC Largest Diameter TOLERANCE
Over But Not Over  
-- 101.6 0.6
101.6 152.4 0.8
152.4 203.2 1.3
203.2 254.0 1.6
254.0 -- 2.3

 

INCH Largest Diameter TOLERANCE
Over But Not Over  
-- 4.00 0.02
4.00 6.00 0.03
6.00 8.00 0.05
8.00 10.00 0.06
10.00 -- 0.09
 

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HEADER MATCH TOLERANCES

SCOPE
1. Header Match Tolerances apply to contours formed by the heading tool and relate to variations of the axis of the header formed contour from the axis of the stock. These tolerances are applied independently of and in addition to all other tolerances.

TOLERANCE
2. Header Match Tolerances are determined by the largest forging diameter and are shown in Table XIII.

MEASURING FOR SHOULDER LENGTH TOLERANCES
3. Measuring for header match is best accomplished by comparing readings of A and B taken at the point of greatest variation and dividing the result by two. (See Figure 20.) The resulting figure equals header match C.
In cases where measurements for determining match tolerances must be made from surfaces of the forging where uneven wearing of the dies has caused surplus stock, accuracy depends on making the proper allowances for these wear-caused surpluses, and eliminating their influence from the computation.
UNITS OF MEASURE
4. Header Match Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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TABLE XIII
HEADER MATCH TOLERANCES

INCH Largest Diameter Tolerance
Over But Not Over  
-- 101.6 0.6
101.6 152.4 0.8
152.4 203.2 1.3
203.2 254.0 1.6
254.0 -- 2.3

 

METRIC Largest Diameter Tolerance
Over But Not Over  
-- 4.00 0.02
4.00 6.00 0.03
6.00 8.00 0.05
8.00 10.00 0.06
10.00 -- 0.09
 

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CONCENTRICITY TOLERANCES (HOLES)

SCOPE
1. Concentricity Tolerances apply to holes formed by the heading tools and relate to variations of the axis of the hole to the axis of the forging.

TOLERANCE
2. Concentricity Tolerances will apply only to hole depths of one diameter or more.
      (a) Hole depths of less than one diameter are controlled by Header Match Tolerance. (See Table XIII.)
      (b) Concentricity Tolerances are independent of Header Match Tolerances (See Table XIV).
MEASURING FOR CONCENTRICITY TOLERANCES
3. Measuring for Concentricity Tolerances is best accomplished by comparing readings of AA and BB in Figure 21 at the point of greatest wall variation.
NOTE: Wall variation is equal to T.I.R.
UNITS OF MEASURE
4. Concentricity Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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TABLE XIV
CONCENTRICITY TOLERANCE (HOLES)

METRIC Depth of Hole Concentricity
TOLERANCE
Total Indicator Reading (Wall Variation TOLERANCE)
Over But Not Over
-- 203.2 1.6 T.I.R. 3.1
203.2 304.8 2.3 T.I.R. 4.6
304.8 -- 3.4 T.I.R. 6.7
INCH Depth of Hole Concentricity
TOLERANCE
Total Indicator Reading (Wall Variation TOLERANCE)
Over But Not Over
-- 8.00 0.06 T.I.R. 0.12
8.00 12.00 0.09 T.I.R. 0.18
12.00 -- 0.13 T.I.R. 0.26
 

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FLASH EXTENSION TOLERANCES

SCOPE
1.  Flash Extension Tolerances apply to the raised ridge of metal (flash) which is forced between the dies.
TOLERANCE
2.  Flash Extension Tolerances are based on many variables including forging , size, material, shape and equipment size. Therefore any table giving limits is not reasonable. Suffice it to say that a flash  extension of 0.06 in. or 1.6 mm is reasonable and normal practice.
MEASURING FOR FLASH EXTENSION TOLERANCE
3.  Normal flash extension is measured from the adjacent surface of the body of the forging to the edge. (See Figure 22.)

     NOTE; Chucking on or locating from flash extension must be avoided.
UNITS OF MEASURE
4. Flash Extension Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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SQUARENESS TOLERANCES

SCOPE
1. Squareness Tolerance relates to deviations from the center line of the stem to the designed angle of the upset, (usually 90°).
TOLERANCE
2. Normal tolerance on squareness is 1°. (See Figure 23.)

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STRAIGHTNESS TOLERANCES

SCOPE
1. Straightness Tolerances relate to deviations of the centerline of the stem and body of the forging from the true centerline. These tolerances are closely related to material supplier's standard.

TOLERANCE
2. Straightness Tolerances are 0.25 inches in 5' or 6.4 mm in 1524 mm.


DRAFT ANGLE TOLERANCES

SCOPE
1.  When draft angles are required on a forging, the size of the angle is generally dependent on the contour of the forging and therefore commonly determined by agreement between purchaser and producer.

TOLERANCE
2.  Draft Angle Tolerances are +2° and -1° on all draft angles, unless modified by prior agreement between purchaser and producer.


RADII TOLERANCES

SCOPE
2. Radii Tolerances relate to variation from radii specifications on all fillet radii and on corner radii.

TOLERANCE
2. Radii Tolerances are plus or minus one-half the specified radii, except where corner radii are affected by trimming in which cases the minus tolerance is commonly modified to allow a square corner to be formed. .

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SURFACE TOLERANCES

SCOPE
1. Surface Tolerances relate to depth of dressouts and scale pits on the forging, based on purchaser's specification or drawing.

TOLERANCE AND CONDITIONS
2.     (a) Localized dressouts or scale pits are commonly allowed on surfaces to be finish machined unless purchaser's specification or drawing states otherwise. Where purchaser specifies stock for machining, dressouts or scale pits are commonly permitted to within 0.06 in. or 1.6 mm of the finished surface or to within one-half of the machining allowance, whichever is smaller.
       (b) Where surfaces of forgings are intended for use in "as forged" condition, dressouts or scale pits are commonly permitted to a depth equal to one-half of the Flange Thickness Tolerance.

TABLE XV
"AS FORGED" SURFACE CONDITION TOLERANCES

METRIC Diameter of Largest Flange Tolerance
Over But Not Over  
0 180.0 0.8
180.0 255.0 1.3
255.0 -- 1.8
INCH Diameter of Largest Flange Tolerance
Over But Not Over  
0 7.00 0.03
7.00 10.00 0.05
10.00 -- 0.07
 

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DEVELOPING FORGING DIMENSIONS FOR MACHINING

Forging dimensions for machining are based on maximum forging tolerance accumulations. Surfaces to be machined are forged oversize externally and undersize internally. In allowing extra stock to clean up with a reasonable minimum cut, the designer must consider all forging tolerances that apply plus a sufficient amount of material. He then establishes forging dimensions adequate to maintain the minimum allowance under the most adverse forging tolerance condition.

The minimum cut required which is the lower limit of each machining allowance, is set arbitrarily. (See Table XV.)

Forgings with corner radii that must be a sharp corner after machining should be designed to assure that the corner will clean up. In most cases making the total machining allowance equal to the corner radius will also take care of the sharp corner. Bear in mind that corner radii smaller than 0.13 in. (larger on large O.D. forgings) will cause excessive die wear and premature die failure not to mention a higher scrap rate due to the difficulty in forging a small hard-to-fill corner.

Forged Diameter Solid Parts (See Figure 24)

Forged Diameter Deep or Through Pierced Parts (See Figure 25)

Forged Thickness Controlled by Header Closure (See Figure 26)

Forged Shoulder Length Controlled by Die Wear

Shrink, Die Sinking and Tolerance (See Figure 27)

Stem Length (See Figure 27)

Overall Length (See Figure 27)

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METRIC CONVERSION
INCH mm
0.03 0.8
0.04 1.1
0.09 2.3
0.18 4.6
1.00 25.4
1.21 30.8

 

METRIC CONVERSION
INCH mm
0.09 2.3
0.12 3.1
1.00 25.4
1.25 31.8
1.50 38.1
4.75 120.7
6.00 152.4
 

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CONVERSION TABLES
FRACTION, DECIMAL AND METRIC EQUIVALENTS

    MM       MM
1/64 - .0156 - 0.397   33/64 - .5156 - 13.097
1/32 - .0313 - 0.794   17/32 - .5313 - 13.494
3/64 - .0469 - 1.191   .6/11 - .5455 - 13.855
1/16 - .0625 - 1.588   35/64 - .5469 - 13.891
5/64 - .0781 - 1.984   5/9 - .5556 - 14.111
1/12 - .0833 - 2.117  

9/16

- .5625 - 14.288
1/11 - .0909 - 2.309   4/7 - .5714 - 14,514
3/32 - .0938 - 2.381   37/64 - .5781 - 14.684
1/10 - .1000 - 2.540   7/12 - .5833 - 14.817
7/64 - .1094 - 2.778   19/32 - .5938 - 15.081
1/9 - .1111 - 2.822   3/5 - .6000 - 15.240
1/8 - .1250 - 3.175   39/64 - .6094 - 15.478
9/64 - .1406 - 3.572   5/8 - .6250 - 15.875
1/7 - .1429 - 3.629   7/11 - .6364 - 16.164
1/6 - .1667 - 4.233   41/64 - .6406 - 16.272
11/64 - .1719 - 4.366   21/32 - .6563 - 16.669
2/11 - .1818 - 4.618   2/3 - .6667 - 16.933
3/16 - .1875 - 4.763   43/64 - .6719 - 17.066
1/5 - .2000 - 5.080   11/16 - .6875 - 17.463
13/64 - .2031 - 5.159   7/10 - .7000 - 17.780
7/32 - .2188 - 5.556   45/64 - .7031 - 17.859
2/9 - .2222 - 5.644   5/7 - .7143 - 18.143
15/64 - .2344 - 5.953   23/32 - .7188 - 18.256
1/4 - .2500 - 6.350   8/11 - .7273 - 18.473
17/64 - .2656 - 6.747   47/64 - .7344 - 18.653
3/11 - .2727 - 6.927   3/4 - .7500 - 19.050
9/32 - .2813 - 7.144   49/64 - .7656 - 19.447
2/7 - .2857 - 7.257   7/9 - .7778 - 19.756
19/64 - .2969 - 7.541   25/32 - .7813 - 19.844
3/10 - .3000 - 7.620   51/64 - .7969 - 20.241
5/16 - .3125 - 7.937   4/5 - .8000 - 20.320
1/3 - .3333 - 8.467   13/16 - .8125 - 20.638
11/32 - .3438 - 8.731   9/11 - .8182 - 20.782
23/64 - .3594 - 9.128   53/64 - .8281 - 21.034
4/11 - .3636 - 9.236   5/6 - .8333 - 21.167
3/8 - .3750 - 9.525   27/32 - .8438 - 21.431
25/64 - .3906 - 9.922   6/7 - .8571 - 21.771
2/5 - .4000 - 10.160   55/64 - .8594 - 21.828
13/32 - .4063 - 10.319   7/8 - .8750 - 22.225
5/12 - .4167 - 10.583   8/9 - .8889 - 22.578
27/64 - .4219 - 10.716   57/64 - .8906 - 22.622
3/7 - .4286 - 10.886   9/10 - .9000 - 22.860
7/16 - .4375 - 11.112   29/32 - .9063 - 23.019
4/9 - .4444 - 11.289   10/11 - .9091 - 23.091
29/64 - .4531 - 11.509   11/12 - .9167 - 23.283
5/11 - .4545 - 11.546   59/64 - .9219 - 23.416
15/32 - .4688 - 11.906   15/16 - .9375 - 23.813
31/64 - .4844 - 12.303   61/64 - .9531 - 24.209
1/2 - .5000 - 12.700   31/32 - .9688 - 24.606
            63/64 - .9844 - 25.003
            1" - 1.0000 - 25.400
To convert a decimal to percentage, carry the decimal point two places to the right. Thus, 63/64, or .9844 equals 98.44%

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Forging Industry Association gratefully acknowledges the cooperation of The American Society of Mechanical Engineers in granting permission to reproduce Guideline Standard Subsection 5-3 entitled "Symbology", originally published in American National Standard Engineering Drawing and Related Documentation Practices "Dimensioning and Tolerancing" ANSI Y14.5-1973.

SYMBOLOGY

GENERAL. This subsection establishes the symbols for specifying geometric characteristics on engineering drawings. Symbols should be of sufficient clarity to meet legibility and reproducibility requirements of American National Standard, Y14.2-1973.

INDIVIDUAL FEATURES   CHARACTERISTIC SYMBOL NOTES
FORM TOLERANCES STRAIGHTNESS 1
FLATNESS 1
ROUNDNESS (CIRCULARITY)  
CYLINDRICITY  
INDIVIDUAL OR RELATED FEATURES PROFILE OF A LINE 2
PROFILE OF A SURFACE 2
RELATED FEATURES ANGULARITY  
PERPENDICULARITY (SQUARENESS)  
LOCATION TOLERANCES PARALLELISM 3
POSITION  
CONCENTRICITY 3.7
SYMMETRY 5
RUNOUT TOLERANCES  CIRCULAR 4
TOTAL 4.6
     
Note:

1) The symbol ~ formerly denoted flatness.

The symbol or formerly denoted flatness and straightness.

2) Considered "related" features where datums are specified.

3) The symbol and formerly denoted parallelism and concentricity, respectively.

4) The symbol without the qualified "CIRCULAR" formerly denoted total runout.

5) Where symmetry applies, it is preferred that the position symbol be used.

6) "TOTAL" must be specified under the feature control symbol.

7) Consider the use of position or runout.

When existing drawings using the above former symbols are continued in use, each former symbol denotes that geometric characteristic which is applicable to the specific type of feature shown

Fig. 28 GEOMETRIC CHARACTERISTIC SYMBOLS

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USE OF NOTES TO SUPPLEMENT SYMBOLS. Situations may arise in which the precise geometric requirement desired cannot be conveyed by symbols. In such instance, a note is used, either separately or supplementing a symbol, to describe the requirement.

SYMBOL CONSTRUCTION. Information related to the construction, form, and proportion of individual symbols described herein are in ANSI Y14.5-1973.

Geometric Characteristic Symbols. The symbols denoting geometric characteristics are shown in Figure 28.

Datum Identifying Symbol. The datum identifying symbol consists of a frame containing the datum reference letter preceded and followed by a dash. See Figure 29. The symbol is associated with the datum feature by one of the methods prescribed in Feature Control symbol Placement, page 64.

Letters of the alphabet (except I, O and Q) are used a datum reference letters. Each datum feature requiring identification should be assigned a different datum reference letter. When datum features requiring identification on a drawing are so numerous as to exhaust the single alpha series, the double alpha series shall be used, that is AA through AZ.

Basic Dimension Symbol. The symbolic means of identifying a basic dimension is to enclose the dimension in a frame, as shown by Figure 30.

MMC and RFS Symbols. The symbols used to designate "maximum material condition" and "regardless of feature size" are shown in Figure 31. In notes, the abbreviations MMC and RFS or their spelled-out terms are used.

Diameter Symbol. The symbol used to designate a diameter is a shown in Figure 31. It precedes the specified tolerance in a feature control symbol. The symbol may be used elsewhere on a drawing in place of the abbreviation DIA.

Projected Tolerance one Symbol. The symbol used to designate a projected tolerance zone is as shown in Figure 31.

Reference Dimension Symbol. The symbolic means of identifying a reference value is by enclosing each such value with parentheses as shown in Figure 31.

Datum Target Symbol. The datum target symbol is a circle divided into four quadrants. The letter placed in the upper left quadrant identifies it associated datum feature. The numeral placed in the lower right quadrant identifies the target. See Figure 32.

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COMBINED SYMBOLS. Individual symbols, datum reference letters, and the desired tolerance are appropriately combined to express a tolerance symbolically.

Feature Control Symbol. A position or form tolerance is stated by means of the feature control symbol consisting of a frame containing the geometric characteristic symbol followed by the allowable tolerance. A vertical line separates the symbol from the tolerance. Where applicable, the tolerance shall be preceded by the diameter symbol and followed by the symbol for MMC or RFS. See Figure 33.

Feature Control Symbol Incorporating Datum References. Where a tolerance of position or form is related to a datum, this relationship is stated in the feature control symbol by placing the datum reference letter following either the geometric characteristic symbol or the tolerance. Vertical lines separate these entries Where applicable, the datum reference letter entry includes the symbol for MMC or RFS. The length of frame is increased as necessary to accommodate requirements. Two methods of referencing datums are illustrated in Figure 34. Methods should not be intermixed on a drawing.

Each datum reference letter (supplemented by the symbol for MMC or RFS where applicable) is entered in the desired order of precedence, from left to right, in the feature control symbol. Datum reference letter entries need not be in alphabetical order. Where a single datum reference is established by multiple datum features, the datum reference letters are separated by a dash between letters. See Figure 35.

A composite feature control symbol is used where more than one tolerance of a given geometric characteristic applies to the same feature. A single entry of the geometric characteristic symbol is followed by each tolerance requirement, one above the other, separated by a horizontal line. See Figure 36.

Combined Feature Control and Datum Identifying Symbol. Where a feature is controlled by a positional or form tolerance and serves as datum feature, the feature control and datum identifying symbols are combined. See Figure 37. In such cases, the length of the frame for the datum identifying symbol may be either the same as that of the feature control symbol or 0.60 inch minimum.

Whenever a feature control symbol and datum identifying symbol are combined, datums included in the feature control symbol portion are not considered part of the datum identifying symbol. In the positional tolerance example, Figure 37, a feature is controlled for position (in relation to datums A and B) and identified as datum C. Whenever datum C is referenced elsewhere on the drawing, the reference applies to datum C, not to datums A and B.

Combined Feature Control and Projected Tolerance Zone Symbol. Where a positional or perpendicularity tolerance is specified as a projected tolerance zone, a frame containing the projected height followed by the appropriate symbol is placed beneath the feature control symbol. See Figure 38.

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FEATURE CONTROL SYMBOL PLACEMENT. The symbol is related to the considered feature by one of the following methods. (See Figure 39.):

    (a) Adding the symbol to a note or dimension pertaining to the feature.

    (b) Running a leader from the feature to the symbol.

    (c) Attaching a side, end, or corner of the symbol frame to an extension line from the feature.

    (d) Attaching a side or end of the symbol frame to the dimension line pertaining to the feature.

IDENTIFICATION OF TOLERANCE ZONE. Where the specified tolerance value represents the diameter of a cylindrical zone, the diameter symbol shall be included in the feature control symbol. Where the tolerance zone is other than a diameter, identification is unnecessary, and the specified tolerance value represents the distance between two parallel straight lines or planes, or the distance between two uniform boundaries, as the specific case may be. For roundness, cylindricity, or runout, the tolerance value shown shall represent the full indicator movement. If desired, the term TOTAL, WIDE ZONE, or ON RADIUS may be used to supplement the tolerance in the appropriate feature control symbol.

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TABULATED TOLERANCES. Where the tolerance in a feature control symbol is to be tabulated, the letter representing the tolerance is preceded by the abbreviation TOL, as shown in Figure 40.

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GUIDELINE TOLERANCES FOR HOT UPSET FORGINGS

INTRODUCTION

Fundamentally, impression die forgings produced on Horizontal Forging Machines (Upsetters) are similar to those produced by Hammers or Presses. Each is the result of forcing metal into cavities in dies which separate at parting lines.

The impression in the ram-operated "Heading Tool" is the equivalent of a Hammer or Press top die. The "grip dies" contain the impressions corresponding to the Hammer or Press bottom die. Grip dies consist of a stationary die and a moving die which, when closed, act to grip the stock and hold it in position for forging. After each workstroke of the machine, these dies open to permit the transfer of stock from one cavity to another in the multiple-impression dies.

After an operation establishes a final contour on a specific portion of an upset forging, subsequent operations may have some effect on that portion. Thus the number and sequence of steps used in shaping the forging must be planned in advance in order that overall tolerance may be anticipated.

Most upset forgings begin with and retain some portion of a hot rolled bar. Permissible mill variations thus have an effect on upset forging tolerances.

As a result of this and other technical considerations, tolerances applying to forgings produced on Forging Machines differ somewhat from those of Hammer and Press forgings.

TOLERANCES

There are practical limitations in dimensions and other characteristics of forged parts or products which vary according to the part or product and the producer\'s equipment. The degree of precision practicable in the manufacture of forged parts or products is dictated by the essential character of forging equipment and unavoidable contingencies in forging operations.

Theoretical exactness is seldom attained, and it is therefore necessary to make allowances for deviations. The tolerances set forth herein represent what the Forging Industry Association believes to be typical within the industry, as determined by actual measurements of forgings produced under normal operating conditions on standard forging equipment.

Experience within the industry shows that dimensional variations in forging are commonly functions of the dimensions involved, and the tolerances herein are based upon this observed fact.

TOLERANCE ACCUMULATION

Where applicable the enclosed tolerances are accumulative. (Example: overall length tolerance = flange thickness tolerance + stem length tolerance.)

The experience of producers and purchasers of forged parts and products indicates that the tolerances set forth herein will provide adequate dimensional accuracy for most applications.

THE TOLERANCES OUTLINED IN THIS BOOKLET ARE GUIDELINES BASED ON HISTORICAL, AVERAGED DATA. THE TERMS OF EACH TRANSACTION BETWEEN A FORGING PRODUCER AND A PURCHASER, INCLUDING TOLERANCES APPLICABLE TO THAT TRANSACTION, MUST BE NEGOTIATED AND CONFIRMED IN ADVANCE OF PRODUCTION.

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GENERAL

All individual tolerances apply to each and every forged part unless specifically noted otherwise.

Tolerances as stated in all tables are considered for use by final inspection departments at the forge plant and/or by receiving or source inspection by the purchaser.

PRINTS AND SPECIFICATIONS

It is important that forging drawings be accurate and complete. The purchaser should indicate his first operation locating points, normally as a part of the drawing, and give prior notice should these points be changed.
 
It is equally important that the purchaser provide drawings of the finish machined part, or equivalent information. This will assist in the design of forging dies and tools, and in establishing most effective final inspection procedures.
Unless the purchaser\'s drawings and specifications direct otherwise, all dimensions are normally assumed to refer to lines intersecting at right angles to each other (commonly referred to as X,, Y, and Z axes). Furthermore, unless the purchaser\'s drawings or specifications direct otherwise, circular shapes are normally assumed to be figures of revolution with a center on an axis, and all circular dimensions are normally shown as diameters.
 
DIMENSIONAL PRACTICES FOR FORGING DRAWINGS
 
At the time of first printing of this publication, a transition period existed dealing with the conversion from the customary decimal inch system to dimensioning to the metric system. The following procedures will apply concerning dimensioning on forging drawings: (1) Metric System _ metric dimensions, on forging drawings, will be extended to one place decimal millimeter for both part dimensions and tolerances (0.1); and (2) Decimal Inch System _ inch units of measure on forging drawings will be extended to two place decimals for both dimensions and tolerances (0.01).
UNITS AND METHODS OF MEASURE METHOD
The forgeman must do much of his measuring (hot inspection) of forgings while they are hot, using practical forge shop instruments such as calipers, rule, straight edge and profile template. The precision of his measurements is therefore limited by the characteristics of such instruments and the conditions under which they must be used.

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UNIT OF MEASURE
Tolerances in this publication are expressed in decimal inch with metric equivalents in the belief that this represents practice most common in the industry at the time of publication.
NOTE: THESE ARE GUIDELINES BASED ON AVERAGES IN THE FORGING INDUSTRY. REFINEMENTS TO THE ENCLOSED TOLERANCES CAN BE MADE IN RELATIONSHIP TO SMALLER DRAFT ANGLES, TIGHTER SQUARENESS, ROUNDNESS, PARALLELISM, STEP DESIGNS AND STRAIGHTNESS. OPERATIONS CAN BE PERFORMED BY FORGE PLANTS TO PROVIDE ADDITIONAL SERVICES WHICH IN MANY CASES REPLACE THE NEED FOR MACHINING.
FLANGE THICKNESS TOLERANCES (Heading Tool Closure)
SCOPE
1. (a) Flange Thickness Tolerances reflect the degree of closure of the heading tool. When more than one flange is formed, these tolerances also apply to the dimension (gap) between flanges.
  (b) Flange Thickness Tolerances are applied separately and independently of other tolerances and are accumulative.
TOLERANCE
2. (a) Tolerances for flange thickness and dimensions (gaps) between flanges are such that the effect is to add stock on both internal and external dimensions. The amount of Flange Thickness Tolerance depends on the flange diameter.
  (b) When two flanges are formed, the tolerance on the dimension (gap) between them is a minus tolerance only, with a value identical to the thickness tolerance for the flange nearest the unforged stem. (See Figure 15)
  (c) Flange Thickness Tolerances are shown in Table VII and Figure 15.
MEASURING FOR FLANGE THICKNESS TOLERANCE
3.   Flange Thickness Tolerance depends on the flange diameter.
UNITS OF MEASURE
4.    Flange Thickness Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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METRIC CONVERSION
INCH mm
0.06 1.5
0.09 2.3
1.25 31.8
1.50 38.1
3.75 95.3
7.00 177.8
8.00 203.2

TABLE VIII
FLANGE THICKNESS TOLERANCES

METRIC Diameters TOLERANCES    
Over But Not Over Plus Minus    
0 180 1.6 --    
180.0 255.0 2.3 --    
255.0 -- 3.4 0.8    

 

INCH Diameters TOLERANCES    
Over But Not Over Plus Minus    
0 7.00 0.06 --    
7.00 10.00 0.09 --    
10.00 -- 0.13 0.03    

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STEM TOLERANCES

SCOPE

1.   Stem Tolerances relate to that portion of the forging from the first flange (flange nearest the unforged end) to the unforged end.

TOLERANCE

2. (a) Stem Tolerances are based on stem length and are expressed as decimals of an inch or mm according to Table IX.
  (b) The diameter of the unheated stem is controlled by mill tolerances. The stem length subjected to forging heat is covered by diameter tolerance (Table XI). The portion of the "heated stem" will vary due to the equipment, process and part geometry. Agreement between the forging producer and forging purchaser should be reached prior to acceptance of order.

MEASURING FOR STEM LENGTH TOLERANCE

3.   Stem Length Tolerances are measured parallel to the axis of the stock from the first flange to the unforged end.
  (b) The diameter of the unheated stem is controlled by mill tolerances. The stem length subjected to forging heat is covered by diameter tolerance (Table XI). The portion of the "heated stem" will vary due to the equipment, process and part geometry. Agreement between the forging producer and forging purchaser should be reached prior to acceptance of order.
 

NOTE:

Line AA, Figure 16 denotes first portion of the forging controlled by the Flange Thickness Tolerance.

UNITS OF MEASURE

4.   Stem Length Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch, in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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METRIC CONVERSION
INCH mm
0.06 1.6
0.09 2.3
0.13 3.4
3.50 88.9
3.75 95.3
10.75 273.1
18.00 457.2

 

TABLE IX
STEM TOLERANCES

METRIC Stem Length TOLERANCES
Over But Not Over Plus Minus
0.0 152.4 1.6 0.08
152.0 254.0 2.3 .8
254.0 508.0 3.4 01.6
508.0 762.0 4.0 1.6
762.0 -- As Agreed --

 

INCH Stem Length TOLERANCES
Over But Not Over Plus Minus
0.00 6.00 0.06 0.03
6.00 10.00 0.09 0.03
10.00 20.00 0.13 0.06
20.00 30.00 0.19 0.06
30.00 -- As Agreed --

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SHOULDER LENGTH TOLERANCES

SCOPE
  1.    Shoulder Length Tolerances apply to portions of the final forging formed as steps to or from a flange and not affected by header closure. Tolerances on the flange thickness, internal length (gap) dimension between flanges and the unforged portion of the stem are toleranced separately and independently of the Shoulder Length Tolerances. Shoulder Length Tolerances include allowances for die wear, shrinkage, die sinking and die polishing variations.
TOLERANCE
   2.Shoulder Length Tolerances are plus values only, expressed in decimals of an inch or mm according to Table X.
MEASURING FOR SHOULDER LENGTH TOLERANCE
   3. Shoulder Length Tolerances are measured parallel to the axis of the original bar.
UNITS OF MEASURE  
4. Shoulder Length Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch, in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next    highest 0.1 in the metric system or 0.01 in the inch system.

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METRIC CONVERSION
INCH mm
0.06 1.6
0.09 2.3
1.00 25.4
1.13 28.8
1.50 38.1
1.75 44.5
3.50 88.9

TABLE X
SHOULDER LENGTH TOLERANCES

METRIC Length Dimensions TOLERANCES
Over But Not Over  
-- 76.2 1.6
76.2 152.4 2.3
152.4 228.6 3.4
228.6 -- 4.1

 

INCH Length Dimensions TOLERANCES
Over But Not Over  
-- 3.00 0.06
3.00 6.00 0.09
6.00 9.00 0.13
9.00 -- 0.16
 

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DIAMETER TOLERANCES

SCOPE
1. (a)Diameter Tolerances are applied separately for each of a forging\'s diameters and only to those diameters formed in the heading tool or dies.
    (b)These tolerances apply only to forgings with circular shape. Tolerances for non-circular forgings are customarily determined by special agreement between purchaser and producer in advance of production.

TOLERANCE
2. (a)Tolerances for all external forged diameters are expressed as plus tolerances only, according to Table XI.
    (b)Tolerances for internal diameters of holes formed by the heading tool are commonly expressed as minus tolerances only according to Table XI.
    (c)Tolerances for Stem Diameters subjected to forging heat are shown in Table XI. Variations in diameter on unheated portions of the stem are commonly governed by mill tolerances.
    (d)Tolerance for shear-cut ends and slight irregularities in diameter on the stem caused by grip dies are commonly determined by special agreement between purchaser and producer.

MEASURING FOR DIAMETER TOLERANCES
3. Diameter Tolerances are commonly applied and measured in a plane 90° from the die parting line (perpendicular to the axis of the stock).

UNITS OF MEASURE
4. Diameter Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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METRIC CONVERSION
INCH mm
0.06 1.6
0.09 2.3
3.50 88.9
3.56 90.5
4.25 108.0
5.00 127.0
6.75 171.5
6.75 203.2

TABLE XI
DIAMETER TOLERANT

METRIC Diameters TOLERANT
Over But Not Over Outside Diameters Inside Diameter
-- 50.8 + 0.8 - 1.6
50.8 177.8 + 1.6 - 2.3
177.8 254.0 + 2.3 - 3.4
254.0 -- + 3.4 - 3.4

 

INCH Diameters TOLERANT
Over But Not Over Outside Diameters Inside Diameter
-- 2.00 + 0.03 - 0.06
2.00 7.00 + 0.06 - 0.09
7.00 10.00 + 0.09 - 0.13
10.00 -- + 0.13 - 0.13
 

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GRIP DIES TOLERANCES

SCOPE
1. Grip Dies Match Tolerances relate to the amount of die displacement in a direction parallel to the parting line of the grip dies. Grip Dies Match describes the results of movement of one die in relation to the other. While this movement is along the die parting line only, it does occur in two ways. Vertical Shift: Where one die is higher than the other. Forward Shift: Where one die is ahead of the other.
TOLERANCE
2. Grip Dies Match Tolerances are based on the largest forging diameter and shown in Table XII. These tolerances are applied independently of and in addition to all other tolerances.
MEASURING FOR SHOULDER LENGTH TOLERANCE
3. Vertical Shift is determined by measuring the difference between AA and BB then dividing by two. (See Fig. 19A.)
Forward Shift is determined by measuring the difference between DD and EE. (See Figure 19B.)
In cases where measurements for determining match tolerances must be made from surfaces of the forging where uneven wearing of the dies has caused surplus stock, accuracy depends on making the proper allowances for these wear-caused surpluses, and eliminating their influence from the computation.
UNITS OF MEASURE
4. Grip Dies Match Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch, in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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TABLE XXII
GRIP DIES MATCH TOLERANCE

METRIC Largest Diameter TOLERANCE
Over But Not Over  
-- 101.6 0.6
101.6 152.4 0.8
152.4 203.2 1.3
203.2 254.0 1.6
254.0 -- 2.3

 

INCH Largest Diameter TOLERANCE
Over But Not Over  
-- 4.00 0.02
4.00 6.00 0.03
6.00 8.00 0.05
8.00 10.00 0.06
10.00 -- 0.09
 

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HEADER MATCH TOLERANCES

SCOPE
1. Header Match Tolerances apply to contours formed by the heading tool and relate to variations of the axis of the header formed contour from the axis of the stock. These tolerances are applied independently of and in addition to all other tolerances.

TOLERANCE
2. Header Match Tolerances are determined by the largest forging diameter and are shown in Table XIII.

MEASURING FOR SHOULDER LENGTH TOLERANCES
3. Measuring for header match is best accomplished by comparing readings of A and B taken at the point of greatest variation and dividing the result by two. (See Figure 20.) The resulting figure equals header match C.
In cases where measurements for determining match tolerances must be made from surfaces of the forging where uneven wearing of the dies has caused surplus stock, accuracy depends on making the proper allowances for these wear-caused surpluses, and eliminating their influence from the computation.
UNITS OF MEASURE
4. Header Match Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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TABLE XIII
HEADER MATCH TOLERANCES

INCH Largest Diameter Tolerance
Over But Not Over  
-- 101.6 0.6
101.6 152.4 0.8
152.4 203.2 1.3
203.2 254.0 1.6
254.0 -- 2.3

 

METRIC Largest Diameter Tolerance
Over But Not Over  
-- 4.00 0.02
4.00 6.00 0.03
6.00 8.00 0.05
8.00 10.00 0.06
10.00 -- 0.09
 

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CONCENTRICITY TOLERANCES (HOLES)

SCOPE
1. Concentricity Tolerances apply to holes formed by the heading tools and relate to variations of the axis of the hole to the axis of the forging.

TOLERANCE
2. Concentricity Tolerances will apply only to hole depths of one diameter or more.
      (a) Hole depths of less than one diameter are controlled by Header Match Tolerance. (See Table XIII.)
      (b) Concentricity Tolerances are independent of Header Match Tolerances (See Table XIV).
MEASURING FOR CONCENTRICITY TOLERANCES
3. Measuring for Concentricity Tolerances is best accomplished by comparing readings of AA and BB in Figure 21 at the point of greatest wall variation.
NOTE: Wall variation is equal to T.I.R.
UNITS OF MEASURE
4. Concentricity Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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TABLE XIV
CONCENTRICITY TOLERANCE (HOLES)

METRIC Depth of Hole Concentricity
TOLERANCE
Total Indicator Reading (Wall Variation TOLERANCE)
Over But Not Over
-- 203.2 1.6 T.I.R. 3.1
203.2 304.8 2.3 T.I.R. 4.6
304.8 -- 3.4 T.I.R. 6.7
INCH Depth of Hole Concentricity
TOLERANCE
Total Indicator Reading (Wall Variation TOLERANCE)
Over But Not Over
-- 8.00 0.06 T.I.R. 0.12
8.00 12.00 0.09 T.I.R. 0.18
12.00 -- 0.13 T.I.R. 0.26
 

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FLASH EXTENSION TOLERANCES

SCOPE
1.  Flash Extension Tolerances apply to the raised ridge of metal (flash) which is forced between the dies.
TOLERANCE
2.  Flash Extension Tolerances are based on many variables including forging , size, material, shape and equipment size. Therefore any table giving limits is not reasonable. Suffice it to say that a flash  extension of 0.06 in. or 1.6 mm is reasonable and normal practice.
MEASURING FOR FLASH EXTENSION TOLERANCE
3.  Normal flash extension is measured from the adjacent surface of the body of the forging to the edge. (See Figure 22.)

     NOTE; Chucking on or locating from flash extension must be avoided.
UNITS OF MEASURE
4. Flash Extension Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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SQUARENESS TOLERANCES

SCOPE
1. Squareness Tolerance relates to deviations from the center line of the stem to the designed angle of the upset, (usually 90°).
TOLERANCE
2. Normal tolerance on squareness is 1°. (See Figure 23.)

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STRAIGHTNESS TOLERANCES

SCOPE
1. Straightness Tolerances relate to deviations of the centerline of the stem and body of the forging from the true centerline. These tolerances are closely related to material supplier\'s standard.

TOLERANCE
2. Straightness Tolerances are 0.25 inches in 5\' or 6.4 mm in 1524 mm.


DRAFT ANGLE TOLERANCES

SCOPE
1.  When draft angles are required on a forging, the size of the angle is generally dependent on the contour of the forging and therefore commonly determined by agreement between purchaser and producer.

TOLERANCE
2.  Draft Angle Tolerances are +2° and -1° on all draft angles, unless modified by prior agreement between purchaser and producer.


RADII TOLERANCES

SCOPE
2. Radii Tolerances relate to variation from radii specifications on all fillet radii and on corner radii.

TOLERANCE
2. Radii Tolerances are plus or minus one-half the specified radii, except where corner radii are affected by trimming in which cases the minus tolerance is commonly modified to allow a square corner to be formed. .

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SURFACE TOLERANCES

SCOPE
1. Surface Tolerances relate to depth of dressouts and scale pits on the forging, based on purchaser\'s specification or drawing.

TOLERANCE AND CONDITIONS
2.     (a) Localized dressouts or scale pits are commonly allowed on surfaces to be finish machined unless purchaser\'s specification or drawing states otherwise. Where purchaser specifies stock for machining, dressouts or scale pits are commonly permitted to within 0.06 in. or 1.6 mm of the finished surface or to within one-half of the machining allowance, whichever is smaller.
       (b) Where surfaces of forgings are intended for use in "as forged" condition, dressouts or scale pits are commonly permitted to a depth equal to one-half of the Flange Thickness Tolerance.

TABLE XV
"AS FORGED" SURFACE CONDITION TOLERANCES

METRIC Diameter of Largest Flange Tolerance
Over But Not Over  
0 180.0 0.8
180.0 255.0 1.3
255.0 -- 1.8
INCH Diameter of Largest Flange Tolerance
Over But Not Over  
0 7.00 0.03
7.00 10.00 0.05
10.00 -- 0.07
 

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DEVELOPING FORGING DIMENSIONS FOR MACHINING

Forging dimensions for machining are based on maximum forging tolerance accumulations. Surfaces to be machined are forged oversize externally and undersize internally. In allowing extra stock to clean up with a reasonable minimum cut, the designer must consider all forging tolerances that apply plus a sufficient amount of material. He then establishes forging dimensions adequate to maintain the minimum allowance under the most adverse forging tolerance condition.

The minimum cut required which is the lower limit of each machining allowance, is set arbitrarily. (See Table XV.)

Forgings with corner radii that must be a sharp corner after machining should be designed to assure that the corner will clean up. In most cases making the total machining allowance equal to the corner radius will also take care of the sharp corner. Bear in mind that corner radii smaller than 0.13 in. (larger on large O.D. forgings) will cause excessive die wear and premature die failure not to mention a higher scrap rate due to the difficulty in forging a small hard-to-fill corner.

Forged Diameter Solid Parts (See Figure 24)

Forged Diameter Deep or Through Pierced Parts (See Figure 25)

Forged Thickness Controlled by Header Closure (See Figure 26)

Forged Shoulder Length Controlled by Die Wear

Shrink, Die Sinking and Tolerance (See Figure 27)

Stem Length (See Figure 27)

Overall Length (See Figure 27)

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METRIC CONVERSION
INCH mm
0.03 0.8
0.04 1.1
0.09 2.3
0.18 4.6
1.00 25.4
1.21 30.8

 

METRIC CONVERSION
INCH mm
0.09 2.3
0.12 3.1
1.00 25.4
1.25 31.8
1.50 38.1
4.75 120.7
6.00 152.4
 

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CONVERSION TABLES
FRACTION, DECIMAL AND METRIC EQUIVALENTS

    MM       MM
1/64 - .0156 - 0.397   33/64 - .5156 - 13.097
1/32 - .0313 - 0.794   17/32 - .5313 - 13.494
3/64 - .0469 - 1.191   .6/11 - .5455 - 13.855
1/16 - .0625 - 1.588   35/64 - .5469 - 13.891
5/64 - .0781 - 1.984   5/9 - .5556 - 14.111
1/12 - .0833 - 2.117  

9/16

- .5625 - 14.288
1/11 - .0909 - 2.309   4/7 - .5714 - 14,514
3/32 - .0938 - 2.381   37/64 - .5781 - 14.684
1/10 - .1000 - 2.540   7/12 - .5833 - 14.817
7/64 - .1094 - 2.778   19/32 - .5938 - 15.081
1/9 - .1111 - 2.822   3/5 - .6000 - 15.240
1/8 - .1250 - 3.175   39/64 - .6094 - 15.478
9/64 - .1406 - 3.572   5/8 - .6250 - 15.875
1/7 - .1429 - 3.629   7/11 - .6364 - 16.164
1/6 - .1667 - 4.233   41/64 - .6406 - 16.272
11/64 - .1719 - 4.366   21/32 - .6563 - 16.669
2/11 - .1818 - 4.618   2/3 - .6667 - 16.933
3/16 - .1875 - 4.763   43/64 - .6719 - 17.066
1/5 - .2000 - 5.080   11/16 - .6875 - 17.463
13/64 - .2031 - 5.159   7/10 - .7000 - 17.780
7/32 - .2188 - 5.556   45/64 - .7031 - 17.859
2/9 - .2222 - 5.644   5/7 - .7143 - 18.143
15/64 - .2344 - 5.953   23/32 - .7188 - 18.256
1/4 - .2500 - 6.350   8/11 - .7273 - 18.473
17/64 - .2656 - 6.747   47/64 - .7344 - 18.653
3/11 - .2727 - 6.927   3/4 - .7500 - 19.050
9/32 - .2813 - 7.144   49/64 - .7656 - 19.447
2/7 - .2857 - 7.257   7/9 - .7778 - 19.756
19/64 - .2969 - 7.541   25/32 - .7813 - 19.844
3/10 - .3000 - 7.620   51/64 - .7969 - 20.241
5/16 - .3125 - 7.937   4/5 - .8000 - 20.320
1/3 - .3333 - 8.467   13/16 - .8125 - 20.638
11/32 - .3438 - 8.731   9/11 - .8182 - 20.782
23/64 - .3594 - 9.128   53/64 - .8281 - 21.034
4/11 - .3636 - 9.236   5/6 - .8333 - 21.167
3/8 - .3750 - 9.525   27/32 - .8438 - 21.431
25/64 - .3906 - 9.922   6/7 - .8571 - 21.771
2/5 - .4000 - 10.160   55/64 - .8594 - 21.828
13/32 - .4063 - 10.319   7/8 - .8750 - 22.225
5/12 - .4167 - 10.583   8/9 - .8889 - 22.578
27/64 - .4219 - 10.716   57/64 - .8906 - 22.622
3/7 - .4286 - 10.886   9/10 - .9000 - 22.860
7/16 - .4375 - 11.112   29/32 - .9063 - 23.019
4/9 - .4444 - 11.289   10/11 - .9091 - 23.091
29/64 - .4531 - 11.509   11/12 - .9167 - 23.283
5/11 - .4545 - 11.546   59/64 - .9219 - 23.416
15/32 - .4688 - 11.906   15/16 - .9375 - 23.813
31/64 - .4844 - 12.303   61/64 - .9531 - 24.209
1/2 - .5000 - 12.700   31/32 - .9688 - 24.606
            63/64 - .9844 - 25.003
            1" - 1.0000 - 25.400
To convert a decimal to percentage, carry the decimal point two places to the right. Thus, 63/64, or .9844 equals 98.44%

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Forging Industry Association gratefully acknowledges the cooperation of The American Society of Mechanical Engineers in granting permission to reproduce Guideline Standard Subsection 5-3 entitled "Symbology", originally published in American National Standard Engineering Drawing and Related Documentation Practices "Dimensioning and Tolerancing" ANSI Y14.5-1973.

SYMBOLOGY

GENERAL. This subsection establishes the symbols for specifying geometric characteristics on engineering drawings. Symbols should be of sufficient clarity to meet legibility and reproducibility requirements of American National Standard, Y14.2-1973.

INDIVIDUAL FEATURES   CHARACTERISTIC SYMBOL NOTES
FORM TOLERANCES STRAIGHTNESS 1
FLATNESS 1
ROUNDNESS (CIRCULARITY)  
CYLINDRICITY  
INDIVIDUAL OR RELATED FEATURES PROFILE OF A LINE 2
PROFILE OF A SURFACE 2
RELATED FEATURES ANGULARITY  
PERPENDICULARITY (SQUARENESS)  
LOCATION TOLERANCES PARALLELISM 3
POSITION  
CONCENTRICITY 3.7
SYMMETRY 5
RUNOUT TOLERANCES  CIRCULAR 4
TOTAL 4.6
     
Note:

1) The symbol ~ formerly denoted flatness.

The symbol or formerly denoted flatness and straightness.

2) Considered "related" features where datums are specified.

3) The symbol and formerly denoted parallelism and concentricity, respectively.

4) The symbol without the qualified "CIRCULAR" formerly denoted total runout.

5) Where symmetry applies, it is preferred that the position symbol be used.

6) "TOTAL" must be specified under the feature control symbol.

7) Consider the use of position or runout.

When existing drawings using the above former symbols are continued in use, each former symbol denotes that geometric characteristic which is applicable to the specific type of feature shown

Fig. 28 GEOMETRIC CHARACTERISTIC SYMBOLS

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USE OF NOTES TO SUPPLEMENT SYMBOLS. Situations may arise in which the precise geometric requirement desired cannot be conveyed by symbols. In such instance, a note is used, either separately or supplementing a symbol, to describe the requirement.

SYMBOL CONSTRUCTION. Information related to the construction, form, and proportion of individual symbols described herein are in ANSI Y14.5-1973.

Geometric Characteristic Symbols. The symbols denoting geometric characteristics are shown in Figure 28.

Datum Identifying Symbol. The datum identifying symbol consists of a frame containing the datum reference letter preceded and followed by a dash. See Figure 29. The symbol is associated with the datum feature by one of the methods prescribed in Feature Control symbol Placement, page 64.

Letters of the alphabet (except I, O and Q) are used a datum reference letters. Each datum feature requiring identification should be assigned a different datum reference letter. When datum features requiring identification on a drawing are so numerous as to exhaust the single alpha series, the double alpha series shall be used, that is AA through AZ.

Basic Dimension Symbol. The symbolic means of identifying a basic dimension is to enclose the dimension in a frame, as shown by Figure 30.

MMC and RFS Symbols. The symbols used to designate "maximum material condition" and "regardless of feature size" are shown in Figure 31. In notes, the abbreviations MMC and RFS or their spelled-out terms are used.

Diameter Symbol. The symbol used to designate a diameter is a shown in Figure 31. It precedes the specified tolerance in a feature control symbol. The symbol may be used elsewhere on a drawing in place of the abbreviation DIA.

Projected Tolerance one Symbol. The symbol used to designate a projected tolerance zone is as shown in Figure 31.

Reference Dimension Symbol. The symbolic means of identifying a reference value is by enclosing each such value with parentheses as shown in Figure 31.

Datum Target Symbol. The datum target symbol is a circle divided into four quadrants. The letter placed in the upper left quadrant identifies it associated datum feature. The numeral placed in the lower right quadrant identifies the target. See Figure 32.

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COMBINED SYMBOLS. Individual symbols, datum reference letters, and the desired tolerance are appropriately combined to express a tolerance symbolically.

Feature Control Symbol. A position or form tolerance is stated by means of the feature control symbol consisting of a frame containing the geometric characteristic symbol followed by the allowable tolerance. A vertical line separates the symbol from the tolerance. Where applicable, the tolerance shall be preceded by the diameter symbol and followed by the symbol for MMC or RFS. See Figure 33.

Feature Control Symbol Incorporating Datum References. Where a tolerance of position or form is related to a datum, this relationship is stated in the feature control symbol by placing the datum reference letter following either the geometric characteristic symbol or the tolerance. Vertical lines separate these entries Where applicable, the datum reference letter entry includes the symbol for MMC or RFS. The length of frame is increased as necessary to accommodate requirements. Two methods of referencing datums are illustrated in Figure 34. Methods should not be intermixed on a drawing.

Each datum reference letter (supplemented by the symbol for MMC or RFS where applicable) is entered in the desired order of precedence, from left to right, in the feature control symbol. Datum reference letter entries need not be in alphabetical order. Where a single datum reference is established by multiple datum features, the datum reference letters are separated by a dash between letters. See Figure 35.

A composite feature control symbol is used where more than one tolerance of a given geometric characteristic applies to the same feature. A single entry of the geometric characteristic symbol is followed by each tolerance requirement, one above the other, separated by a horizontal line. See Figure 36.

Combined Feature Control and Datum Identifying Symbol. Where a feature is controlled by a positional or form tolerance and serves as datum feature, the feature control and datum identifying symbols are combined. See Figure 37. In such cases, the length of the frame for the datum identifying symbol may be either the same as that of the feature control symbol or 0.60 inch minimum.

Whenever a feature control symbol and datum identifying symbol are combined, datums included in the feature control symbol portion are not considered part of the datum identifying symbol. In the positional tolerance example, Figure 37, a feature is controlled for position (in relation to datums A and B) and identified as datum C. Whenever datum C is referenced elsewhere on the drawing, the reference applies to datum C, not to datums A and B.

Combined Feature Control and Projected Tolerance Zone Symbol. Where a positional or perpendicularity tolerance is specified as a projected tolerance zone, a frame containing the projected height followed by the appropriate symbol is placed beneath the feature control symbol. See Figure 38.

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FEATURE CONTROL SYMBOL PLACEMENT. The symbol is related to the considered feature by one of the following methods. (See Figure 39.):

    (a) Adding the symbol to a note or dimension pertaining to the feature.

    (b) Running a leader from the feature to the symbol.

    (c) Attaching a side, end, or corner of the symbol frame to an extension line from the feature.

    (d) Attaching a side or end of the symbol frame to the dimension line pertaining to the feature.

IDENTIFICATION OF TOLERANCE ZONE. Where the specified tolerance value represents the diameter of a cylindrical zone, the diameter symbol shall be included in the feature control symbol. Where the tolerance zone is other than a diameter, identification is unnecessary, and the specified tolerance value represents the distance between two parallel straight lines or planes, or the distance between two uniform boundaries, as the specific case may be. For roundness, cylindricity, or runout, the tolerance value shown shall represent the full indicator movement. If desired, the term TOTAL, WIDE ZONE, or ON RADIUS may be used to supplement the tolerance in the appropriate feature control symbol.

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TABULATED TOLERANCES. Where the tolerance in a feature control symbol is to be tabulated, the letter representing the tolerance is preceded by the abbreviation TOL, as shown in Figure 40.

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GUIDELINE TOLERANCES FOR HOT UPSET FORGINGS

INTRODUCTION

Fundamentally, impression die forgings produced on Horizontal Forging Machines (Upsetters) are similar to those produced by Hammers or Presses. Each is the result of forcing metal into cavities in dies which separate at parting lines.

The impression in the ram-operated "Heading Tool" is the equivalent of a Hammer or Press top die. The "grip dies" contain the impressions corresponding to the Hammer or Press bottom die. Grip dies consist of a stationary die and a moving die which, when closed, act to grip the stock and hold it in position for forging. After each workstroke of the machine, these dies open to permit the transfer of stock from one cavity to another in the multiple-impression dies.

After an operation establishes a final contour on a specific portion of an upset forging, subsequent operations may have some effect on that portion. Thus the number and sequence of steps used in shaping the forging must be planned in advance in order that overall tolerance may be anticipated.

Most upset forgings begin with and retain some portion of a hot rolled bar. Permissible mill variations thus have an effect on upset forging tolerances.

As a result of this and other technical considerations, tolerances applying to forgings produced on Forging Machines differ somewhat from those of Hammer and Press forgings.

TOLERANCES

There are practical limitations in dimensions and other characteristics of forged parts or products which vary according to the part or product and the producer\'s equipment. The degree of precision practicable in the manufacture of forged parts or products is dictated by the essential character of forging equipment and unavoidable contingencies in forging operations.

Theoretical exactness is seldom attained, and it is therefore necessary to make allowances for deviations. The tolerances set forth herein represent what the Forging Industry Association believes to be typical within the industry, as determined by actual measurements of forgings produced under normal operating conditions on standard forging equipment.

Experience within the industry shows that dimensional variations in forging are commonly functions of the dimensions involved, and the tolerances herein are based upon this observed fact.

TOLERANCE ACCUMULATION

Where applicable the enclosed tolerances are accumulative. (Example: overall length tolerance = flange thickness tolerance + stem length tolerance.)

The experience of producers and purchasers of forged parts and products indicates that the tolerances set forth herein will provide adequate dimensional accuracy for most applications.

THE TOLERANCES OUTLINED IN THIS BOOKLET ARE GUIDELINES BASED ON HISTORICAL, AVERAGED DATA. THE TERMS OF EACH TRANSACTION BETWEEN A FORGING PRODUCER AND A PURCHASER, INCLUDING TOLERANCES APPLICABLE TO THAT TRANSACTION, MUST BE NEGOTIATED AND CONFIRMED IN ADVANCE OF PRODUCTION.

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GENERAL

All individual tolerances apply to each and every forged part unless specifically noted otherwise.

Tolerances as stated in all tables are considered for use by final inspection departments at the forge plant and/or by receiving or source inspection by the purchaser.

PRINTS AND SPECIFICATIONS

It is important that forging drawings be accurate and complete. The purchaser should indicate his first operation locating points, normally as a part of the drawing, and give prior notice should these points be changed.
 
It is equally important that the purchaser provide drawings of the finish machined part, or equivalent information. This will assist in the design of forging dies and tools, and in establishing most effective final inspection procedures.
Unless the purchaser\'s drawings and specifications direct otherwise, all dimensions are normally assumed to refer to lines intersecting at right angles to each other (commonly referred to as X,, Y, and Z axes). Furthermore, unless the purchaser\'s drawings or specifications direct otherwise, circular shapes are normally assumed to be figures of revolution with a center on an axis, and all circular dimensions are normally shown as diameters.
 
DIMENSIONAL PRACTICES FOR FORGING DRAWINGS
 
At the time of first printing of this publication, a transition period existed dealing with the conversion from the customary decimal inch system to dimensioning to the metric system. The following procedures will apply concerning dimensioning on forging drawings: (1) Metric System _ metric dimensions, on forging drawings, will be extended to one place decimal millimeter for both part dimensions and tolerances (0.1); and (2) Decimal Inch System _ inch units of measure on forging drawings will be extended to two place decimals for both dimensions and tolerances (0.01).
UNITS AND METHODS OF MEASURE METHOD
The forgeman must do much of his measuring (hot inspection) of forgings while they are hot, using practical forge shop instruments such as calipers, rule, straight edge and profile template. The precision of his measurements is therefore limited by the characteristics of such instruments and the conditions under which they must be used.

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UNIT OF MEASURE
Tolerances in this publication are expressed in decimal inch with metric equivalents in the belief that this represents practice most common in the industry at the time of publication.
NOTE: THESE ARE GUIDELINES BASED ON AVERAGES IN THE FORGING INDUSTRY. REFINEMENTS TO THE ENCLOSED TOLERANCES CAN BE MADE IN RELATIONSHIP TO SMALLER DRAFT ANGLES, TIGHTER SQUARENESS, ROUNDNESS, PARALLELISM, STEP DESIGNS AND STRAIGHTNESS. OPERATIONS CAN BE PERFORMED BY FORGE PLANTS TO PROVIDE ADDITIONAL SERVICES WHICH IN MANY CASES REPLACE THE NEED FOR MACHINING.
FLANGE THICKNESS TOLERANCES (Heading Tool Closure)
SCOPE
1. (a) Flange Thickness Tolerances reflect the degree of closure of the heading tool. When more than one flange is formed, these tolerances also apply to the dimension (gap) between flanges.
  (b) Flange Thickness Tolerances are applied separately and independently of other tolerances and are accumulative.
TOLERANCE
2. (a) Tolerances for flange thickness and dimensions (gaps) between flanges are such that the effect is to add stock on both internal and external dimensions. The amount of Flange Thickness Tolerance depends on the flange diameter.
  (b) When two flanges are formed, the tolerance on the dimension (gap) between them is a minus tolerance only, with a value identical to the thickness tolerance for the flange nearest the unforged stem. (See Figure 15)
  (c) Flange Thickness Tolerances are shown in Table VII and Figure 15.
MEASURING FOR FLANGE THICKNESS TOLERANCE
3.   Flange Thickness Tolerance depends on the flange diameter.
UNITS OF MEASURE
4.    Flange Thickness Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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METRIC CONVERSION
INCH mm
0.06 1.5
0.09 2.3
1.25 31.8
1.50 38.1
3.75 95.3
7.00 177.8
8.00 203.2

TABLE VIII
FLANGE THICKNESS TOLERANCES

METRIC Diameters TOLERANCES    
Over But Not Over Plus Minus    
0 180 1.6 --    
180.0 255.0 2.3 --    
255.0 -- 3.4 0.8    

 

INCH Diameters TOLERANCES    
Over But Not Over Plus Minus    
0 7.00 0.06 --    
7.00 10.00 0.09 --    
10.00 -- 0.13 0.03    

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STEM TOLERANCES

SCOPE

1.   Stem Tolerances relate to that portion of the forging from the first flange (flange nearest the unforged end) to the unforged end.

TOLERANCE

2. (a) Stem Tolerances are based on stem length and are expressed as decimals of an inch or mm according to Table IX.
  (b) The diameter of the unheated stem is controlled by mill tolerances. The stem length subjected to forging heat is covered by diameter tolerance (Table XI). The portion of the "heated stem" will vary due to the equipment, process and part geometry. Agreement between the forging producer and forging purchaser should be reached prior to acceptance of order.

MEASURING FOR STEM LENGTH TOLERANCE

3.   Stem Length Tolerances are measured parallel to the axis of the stock from the first flange to the unforged end.
  (b) The diameter of the unheated stem is controlled by mill tolerances. The stem length subjected to forging heat is covered by diameter tolerance (Table XI). The portion of the "heated stem" will vary due to the equipment, process and part geometry. Agreement between the forging producer and forging purchaser should be reached prior to acceptance of order.
 

NOTE:

Line AA, Figure 16 denotes first portion of the forging controlled by the Flange Thickness Tolerance.

UNITS OF MEASURE

4.   Stem Length Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch, in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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METRIC CONVERSION
INCH mm
0.06 1.6
0.09 2.3
0.13 3.4
3.50 88.9
3.75 95.3
10.75 273.1
18.00 457.2

 

TABLE IX
STEM TOLERANCES

METRIC Stem Length TOLERANCES
Over But Not Over Plus Minus
0.0 152.4 1.6 0.08
152.0 254.0 2.3 .8
254.0 508.0 3.4 01.6
508.0 762.0 4.0 1.6
762.0 -- As Agreed --

 

INCH Stem Length TOLERANCES
Over But Not Over Plus Minus
0.00 6.00 0.06 0.03
6.00 10.00 0.09 0.03
10.00 20.00 0.13 0.06
20.00 30.00 0.19 0.06
30.00 -- As Agreed --

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SHOULDER LENGTH TOLERANCES

SCOPE
  1.    Shoulder Length Tolerances apply to portions of the final forging formed as steps to or from a flange and not affected by header closure. Tolerances on the flange thickness, internal length (gap) dimension between flanges and the unforged portion of the stem are toleranced separately and independently of the Shoulder Length Tolerances. Shoulder Length Tolerances include allowances for die wear, shrinkage, die sinking and die polishing variations.
TOLERANCE
   2.Shoulder Length Tolerances are plus values only, expressed in decimals of an inch or mm according to Table X.
MEASURING FOR SHOULDER LENGTH TOLERANCE
   3. Shoulder Length Tolerances are measured parallel to the axis of the original bar.
UNITS OF MEASURE  
4. Shoulder Length Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch, in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next    highest 0.1 in the metric system or 0.01 in the inch system.

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METRIC CONVERSION
INCH mm
0.06 1.6
0.09 2.3
1.00 25.4
1.13 28.8
1.50 38.1
1.75 44.5
3.50 88.9

TABLE X
SHOULDER LENGTH TOLERANCES

METRIC Length Dimensions TOLERANCES
Over But Not Over  
-- 76.2 1.6
76.2 152.4 2.3
152.4 228.6 3.4
228.6 -- 4.1

 

INCH Length Dimensions TOLERANCES
Over But Not Over  
-- 3.00 0.06
3.00 6.00 0.09
6.00 9.00 0.13
9.00 -- 0.16
 

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DIAMETER TOLERANCES

SCOPE
1. (a)Diameter Tolerances are applied separately for each of a forging\'s diameters and only to those diameters formed in the heading tool or dies.
    (b)These tolerances apply only to forgings with circular shape. Tolerances for non-circular forgings are customarily determined by special agreement between purchaser and producer in advance of production.

TOLERANCE
2. (a)Tolerances for all external forged diameters are expressed as plus tolerances only, according to Table XI.
    (b)Tolerances for internal diameters of holes formed by the heading tool are commonly expressed as minus tolerances only according to Table XI.
    (c)Tolerances for Stem Diameters subjected to forging heat are shown in Table XI. Variations in diameter on unheated portions of the stem are commonly governed by mill tolerances.
    (d)Tolerance for shear-cut ends and slight irregularities in diameter on the stem caused by grip dies are commonly determined by special agreement between purchaser and producer.

MEASURING FOR DIAMETER TOLERANCES
3. Diameter Tolerances are commonly applied and measured in a plane 90° from the die parting line (perpendicular to the axis of the stock).

UNITS OF MEASURE
4. Diameter Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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METRIC CONVERSION
INCH mm
0.06 1.6
0.09 2.3
3.50 88.9
3.56 90.5
4.25 108.0
5.00 127.0
6.75 171.5
6.75 203.2

TABLE XI
DIAMETER TOLERANT

METRIC Diameters TOLERANT
Over But Not Over Outside Diameters Inside Diameter
-- 50.8 + 0.8 - 1.6
50.8 177.8 + 1.6 - 2.3
177.8 254.0 + 2.3 - 3.4
254.0 -- + 3.4 - 3.4

 

INCH Diameters TOLERANT
Over But Not Over Outside Diameters Inside Diameter
-- 2.00 + 0.03 - 0.06
2.00 7.00 + 0.06 - 0.09
7.00 10.00 + 0.09 - 0.13
10.00 -- + 0.13 - 0.13
 

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GRIP DIES TOLERANCES

SCOPE
1. Grip Dies Match Tolerances relate to the amount of die displacement in a direction parallel to the parting line of the grip dies. Grip Dies Match describes the results of movement of one die in relation to the other. While this movement is along the die parting line only, it does occur in two ways. Vertical Shift: Where one die is higher than the other. Forward Shift: Where one die is ahead of the other.
TOLERANCE
2. Grip Dies Match Tolerances are based on the largest forging diameter and shown in Table XII. These tolerances are applied independently of and in addition to all other tolerances.
MEASURING FOR SHOULDER LENGTH TOLERANCE
3. Vertical Shift is determined by measuring the difference between AA and BB then dividing by two. (See Fig. 19A.)
Forward Shift is determined by measuring the difference between DD and EE. (See Figure 19B.)
In cases where measurements for determining match tolerances must be made from surfaces of the forging where uneven wearing of the dies has caused surplus stock, accuracy depends on making the proper allowances for these wear-caused surpluses, and eliminating their influence from the computation.
UNITS OF MEASURE
4. Grip Dies Match Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch, in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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TABLE XXII
GRIP DIES MATCH TOLERANCE

METRIC Largest Diameter TOLERANCE
Over But Not Over  
-- 101.6 0.6
101.6 152.4 0.8
152.4 203.2 1.3
203.2 254.0 1.6
254.0 -- 2.3

 

INCH Largest Diameter TOLERANCE
Over But Not Over  
-- 4.00 0.02
4.00 6.00 0.03
6.00 8.00 0.05
8.00 10.00 0.06
10.00 -- 0.09
 

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HEADER MATCH TOLERANCES

SCOPE
1. Header Match Tolerances apply to contours formed by the heading tool and relate to variations of the axis of the header formed contour from the axis of the stock. These tolerances are applied independently of and in addition to all other tolerances.

TOLERANCE
2. Header Match Tolerances are determined by the largest forging diameter and are shown in Table XIII.

MEASURING FOR SHOULDER LENGTH TOLERANCES
3. Measuring for header match is best accomplished by comparing readings of A and B taken at the point of greatest variation and dividing the result by two. (See Figure 20.) The resulting figure equals header match C.
In cases where measurements for determining match tolerances must be made from surfaces of the forging where uneven wearing of the dies has caused surplus stock, accuracy depends on making the proper allowances for these wear-caused surpluses, and eliminating their influence from the computation.
UNITS OF MEASURE
4. Header Match Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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TABLE XIII
HEADER MATCH TOLERANCES

INCH Largest Diameter Tolerance
Over But Not Over  
-- 101.6 0.6
101.6 152.4 0.8
152.4 203.2 1.3
203.2 254.0 1.6
254.0 -- 2.3

 

METRIC Largest Diameter Tolerance
Over But Not Over  
-- 4.00 0.02
4.00 6.00 0.03
6.00 8.00 0.05
8.00 10.00 0.06
10.00 -- 0.09
 

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CONCENTRICITY TOLERANCES (HOLES)

SCOPE
1. Concentricity Tolerances apply to holes formed by the heading tools and relate to variations of the axis of the hole to the axis of the forging.

TOLERANCE
2. Concentricity Tolerances will apply only to hole depths of one diameter or more.
      (a) Hole depths of less than one diameter are controlled by Header Match Tolerance. (See Table XIII.)
      (b) Concentricity Tolerances are independent of Header Match Tolerances (See Table XIV).
MEASURING FOR CONCENTRICITY TOLERANCES
3. Measuring for Concentricity Tolerances is best accomplished by comparing readings of AA and BB in Figure 21 at the point of greatest wall variation.
NOTE: Wall variation is equal to T.I.R.
UNITS OF MEASURE
4. Concentricity Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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TABLE XIV
CONCENTRICITY TOLERANCE (HOLES)

METRIC Depth of Hole Concentricity
TOLERANCE
Total Indicator Reading (Wall Variation TOLERANCE)
Over But Not Over
-- 203.2 1.6 T.I.R. 3.1
203.2 304.8 2.3 T.I.R. 4.6
304.8 -- 3.4 T.I.R. 6.7
INCH Depth of Hole Concentricity
TOLERANCE
Total Indicator Reading (Wall Variation TOLERANCE)
Over But Not Over
-- 8.00 0.06 T.I.R. 0.12
8.00 12.00 0.09 T.I.R. 0.18
12.00 -- 0.13 T.I.R. 0.26
 

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FLASH EXTENSION TOLERANCES

SCOPE
1.  Flash Extension Tolerances apply to the raised ridge of metal (flash) which is forced between the dies.
TOLERANCE
2.  Flash Extension Tolerances are based on many variables including forging , size, material, shape and equipment size. Therefore any table giving limits is not reasonable. Suffice it to say that a flash  extension of 0.06 in. or 1.6 mm is reasonable and normal practice.
MEASURING FOR FLASH EXTENSION TOLERANCE
3.  Normal flash extension is measured from the adjacent surface of the body of the forging to the edge. (See Figure 22.)

     NOTE; Chucking on or locating from flash extension must be avoided.
UNITS OF MEASURE
4. Flash Extension Tolerances are expressed as decimal millimeter in units of 0.1 mm or greater and expressed as decimal inch in units of 0.01 or greater. Decimals used in computing tolerances are totaled and raised to the next highest 0.1 in the metric system or 0.01 in the inch system.

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SQUARENESS TOLERANCES

SCOPE
1. Squareness Tolerance relates to deviations from the center line of the stem to the designed angle of the upset, (usually 90°).
TOLERANCE
2. Normal tolerance on squareness is 1°. (See Figure 23.)

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STRAIGHTNESS TOLERANCES

SCOPE
1. Straightness Tolerances relate to deviations of the centerline of the stem and body of the forging from the true centerline. These tolerances are closely related to material supplier\'s standard.

TOLERANCE
2. Straightness Tolerances are 0.25 inches in 5\' or 6.4 mm in 1524 mm.


DRAFT ANGLE TOLERANCES

SCOPE
1.  When draft angles are required on a forging, the size of the angle is generally dependent on the contour of the forging and therefore commonly determined by agreement between purchaser and producer.

TOLERANCE
2.  Draft Angle Tolerances are +2° and -1° on all draft angles, unless modified by prior agreement between purchaser and producer.


RADII TOLERANCES

SCOPE
2. Radii Tolerances relate to variation from radii specifications on all fillet radii and on corner radii.

TOLERANCE
2. Radii Tolerances are plus or minus one-half the specified radii, except where corner radii are affected by trimming in which cases the minus tolerance is commonly modified to allow a square corner to be formed. .

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SURFACE TOLERANCES

SCOPE
1. Surface Tolerances relate to depth of dressouts and scale pits on the forging, based on purchaser\'s specification or drawing.

TOLERANCE AND CONDITIONS
2.     (a) Localized dressouts or scale pits are commonly allowed on surfaces to be finish machined unless purchaser\'s specification or drawing states otherwise. Where purchaser specifies stock for machining, dressouts or scale pits are commonly permitted to within 0.06 in. or 1.6 mm of the finished surface or to within one-half of the machining allowance, whichever is smaller.
       (b) Where surfaces of forgings are intended for use in "as forged" condition, dressouts or scale pits are commonly permitted to a depth equal to one-half of the Flange Thickness Tolerance.

TABLE XV
"AS FORGED" SURFACE CONDITION TOLERANCES

METRIC Diameter of Largest Flange Tolerance
Over But Not Over  
0 180.0 0.8
180.0 255.0 1.3
255.0 -- 1.8
INCH Diameter of Largest Flange Tolerance
Over But Not Over  
0 7.00 0.03
7.00 10.00 0.05
10.00 -- 0.07
 

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DEVELOPING FORGING DIMENSIONS FOR MACHINING

Forging dimensions for machining are based on maximum forging tolerance accumulations. Surfaces to be machined are forged oversize externally and undersize internally. In allowing extra stock to clean up with a reasonable minimum cut, the designer must consider all forging tolerances that apply plus a sufficient amount of material. He then establishes forging dimensions adequate to maintain the minimum allowance under the most adverse forging tolerance condition.

The minimum cut required which is the lower limit of each machining allowance, is set arbitrarily. (See Table XV.)

Forgings with corner radii that must be a sharp corner after machining should be designed to assure that the corner will clean up. In most cases making the total machining allowance equal to the corner radius will also take care of the sharp corner. Bear in mind that corner radii smaller than 0.13 in. (larger on large O.D. forgings) will cause excessive die wear and premature die failure not to mention a higher scrap rate due to the difficulty in forging a small hard-to-fill corner.

Forged Diameter Solid Parts (See Figure 24)

Forged Diameter Deep or Through Pierced Parts (See Figure 25)

Forged Thickness Controlled by Header Closure (See Figure 26)

Forged Shoulder Length Controlled by Die Wear

Shrink, Die Sinking and Tolerance (See Figure 27)

Stem Length (See Figure 27)

Overall Length (See Figure 27)

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METRIC CONVERSION
INCH mm
0.03 0.8
0.04 1.1
0.09 2.3
0.18 4.6
1.00 25.4
1.21 30.8

 

METRIC CONVERSION
INCH mm
0.09 2.3
0.12 3.1
1.00 25.4
1.25 31.8
1.50 38.1
4.75 120.7
6.00 152.4
 

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CONVERSION TABLES
FRACTION, DECIMAL AND METRIC EQUIVALENTS

    MM       MM
1/64 - .0156 - 0.397   33/64 - .5156 - 13.097
1/32 - .0313 - 0.794   17/32 - .5313 - 13.494
3/64 - .0469 - 1.191   .6/11 - .5455 - 13.855
1/16 - .0625 - 1.588   35/64 - .5469 - 13.891
5/64 - .0781 - 1.984   5/9 - .5556 - 14.111
1/12 - .0833 - 2.117  

9/16

- .5625 - 14.288
1/11 - .0909 - 2.309   4/7 - .5714 - 14,514
3/32 - .0938 - 2.381   37/64 - .5781 - 14.684
1/10 - .1000 - 2.540   7/12 - .5833 - 14.817
7/64 - .1094 - 2.778   19/32 - .5938 - 15.081
1/9 - .1111 - 2.822   3/5 - .6000 - 15.240
1/8 - .1250 - 3.175   39/64 - .6094 - 15.478
9/64 - .1406 - 3.572   5/8 - .6250 - 15.875
1/7 - .1429 - 3.629   7/11 - .6364 - 16.164
1/6 - .1667 - 4.233   41/64 - .6406 - 16.272
11/64 - .1719 - 4.366   21/32 - .6563 - 16.669
2/11 - .1818 - 4.618   2/3 - .6667 - 16.933
3/16 - .1875 - 4.763   43/64 - .6719 - 17.066
1/5 - .2000 - 5.080   11/16 - .6875 - 17.463
13/64 - .2031 - 5.159   7/10 - .7000 - 17.780
7/32 - .2188 - 5.556   45/64 - .7031 - 17.859
2/9 - .2222 - 5.644   5/7 - .7143 - 18.143
15/64 - .2344 - 5.953   23/32 - .7188 - 18.256
1/4 - .2500 - 6.350   8/11 - .7273 - 18.473
17/64 - .2656 - 6.747   47/64 - .7344 - 18.653
3/11 - .2727 - 6.927   3/4 - .7500 - 19.050
9/32 - .2813 - 7.144   49/64 - .7656 - 19.447
2/7 - .2857 - 7.257   7/9 - .7778 - 19.756
19/64 - .2969 - 7.541   25/32 - .7813 - 19.844
3/10 - .3000 - 7.620   51/64 - .7969 - 20.241
5/16 - .3125 - 7.937   4/5 - .8000 - 20.320
1/3 - .3333 - 8.467   13/16 - .8125 - 20.638
11/32 - .3438 - 8.731   9/11 - .8182 - 20.782
23/64 - .3594 - 9.128   53/64 - .8281 - 21.034
4/11 - .3636 - 9.236   5/6 - .8333 - 21.167
3/8 - .3750 - 9.525   27/32 - .8438 - 21.431
25/64 - .3906 - 9.922   6/7 - .8571 - 21.771
2/5 - .4000 - 10.160   55/64 - .8594 - 21.828
13/32 - .4063 - 10.319   7/8 - .8750 - 22.225
5/12 - .4167 - 10.583   8/9 - .8889 - 22.578
27/64 - .4219 - 10.716   57/64 - .8906 - 22.622
3/7 - .4286 - 10.886   9/10 - .9000 - 22.860
7/16 - .4375 - 11.112   29/32 - .9063 - 23.019
4/9 - .4444 - 11.289   10/11 - .9091 - 23.091
29/64 - .4531 - 11.509   11/12 - .9167 - 23.283
5/11 - .4545 - 11.546   59/64 - .9219 - 23.416
15/32 - .4688 - 11.906   15/16 - .9375 - 23.813
31/64 - .4844 - 12.303   61/64 - .9531 - 24.209
1/2 - .5000 - 12.700   31/32 - .9688 - 24.606
            63/64 - .9844 - 25.003
            1" - 1.0000 - 25.400
To convert a decimal to percentage, carry the decimal point two places to the right. Thus, 63/64, or .9844 equals 98.44%

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Forging Industry Association gratefully acknowledges the cooperation of The American Society of Mechanical Engineers in granting permission to reproduce Guideline Standard Subsection 5-3 entitled "Symbology", originally published in American National Standard Engineering Drawing and Related Documentation Practices "Dimensioning and Tolerancing" ANSI Y14.5-1973.

SYMBOLOGY

GENERAL. This subsection establishes the symbols for specifying geometric characteristics on engineering drawings. Symbols should be of sufficient clarity to meet legibility and reproducibility requirements of American National Standard, Y14.2-1973.

INDIVIDUAL FEATURES   CHARACTERISTIC SYMBOL NOTES
FORM TOLERANCES STRAIGHTNESS 1
FLATNESS 1
ROUNDNESS (CIRCULARITY)  
CYLINDRICITY  
INDIVIDUAL OR RELATED FEATURES PROFILE OF A LINE 2
PROFILE OF A SURFACE 2
RELATED FEATURES ANGULARITY  
PERPENDICULARITY (SQUARENESS)  
LOCATION TOLERANCES PARALLELISM 3
POSITION  
CONCENTRICITY 3.7
SYMMETRY 5
RUNOUT TOLERANCES  CIRCULAR 4
TOTAL 4.6
     
Note:

1) The symbol ~ formerly denoted flatness.

The symbol or formerly denoted flatness and straightness.

2) Considered "related" features where datums are specified.

3) The symbol and formerly denoted parallelism and concentricity, respectively.

4) The symbol without the qualified "CIRCULAR" formerly denoted total runout.

5) Where symmetry applies, it is preferred that the position symbol be used.

6) "TOTAL" must be specified under the feature control symbol.

7) Consider the use of position or runout.

When existing drawings using the above former symbols are continued in use, each former symbol denotes that geometric characteristic which is applicable to the specific type of feature shown

Fig. 28 GEOMETRIC CHARACTERISTIC SYMBOLS

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USE OF NOTES TO SUPPLEMENT SYMBOLS. Situations may arise in which the precise geometric requirement desired cannot be conveyed by symbols. In such instance, a note is used, either separately or supplementing a symbol, to describe the requirement.

SYMBOL CONSTRUCTION. Information related to the construction, form, and proportion of individual symbols described herein are in ANSI Y14.5-1973.

Geometric Characteristic Symbols. The symbols denoting geometric characteristics are shown in Figure 28.

Datum Identifying Symbol. The datum identifying symbol consists of a frame containing the datum reference letter preceded and followed by a dash. See Figure 29. The symbol is associated with the datum feature by one of the methods prescribed in Feature Control symbol Placement, page 64.

Letters of the alphabet (except I, O and Q) are used a datum reference letters. Each datum feature requiring identification should be assigned a different datum reference letter. When datum features requiring identification on a drawing are so numerous as to exhaust the single alpha series, the double alpha series shall be used, that is AA through AZ.

Basic Dimension Symbol. The symbolic means of identifying a basic dimension is to enclose the dimension in a frame, as shown by Figure 30.

MMC and RFS Symbols. The symbols used to designate "maximum material condition" and "regardless of feature size" are shown in Figure 31. In notes, the abbreviations MMC and RFS or their spelled-out terms are used.

Diameter Symbol. The symbol used to designate a diameter is a shown in Figure 31. It precedes the specified tolerance in a feature control symbol. The symbol may be used elsewhere on a drawing in place of the abbreviation DIA.

Projected Tolerance one Symbol. The symbol used to designate a projected tolerance zone is as shown in Figure 31.

Reference Dimension Symbol. The symbolic means of identifying a reference value is by enclosing each such value with parentheses as shown in Figure 31.

Datum Target Symbol. The datum target symbol is a circle divided into four quadrants. The letter placed in the upper left quadrant identifies it associated datum feature. The numeral placed in the lower right quadrant identifies the target. See Figure 32.

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COMBINED SYMBOLS. Individual symbols, datum reference letters, and the desired tolerance are appropriately combined to express a tolerance symbolically.

Feature Control Symbol. A position or form tolerance is stated by means of the feature control symbol consisting of a frame containing the geometric characteristic symbol followed by the allowable tolerance. A vertical line separates the symbol from the tolerance. Where applicable, the tolerance shall be preceded by the diameter symbol and followed by the symbol for MMC or RFS. See Figure 33.

Feature Control Symbol Incorporating Datum References. Where a tolerance of position or form is related to a datum, this relationship is stated in the feature control symbol by placing the datum reference letter following either the geometric characteristic symbol or the tolerance. Vertical lines separate these entries Where applicable, the datum reference letter entry includes the symbol for MMC or RFS. The length of frame is increased as necessary to accommodate requirements. Two methods of referencing datums are illustrated in Figure 34. Methods should not be intermixed on a drawing.

Each datum reference letter (supplemented by the symbol for MMC or RFS where applicable) is entered in the desired order of precedence, from left to right, in the feature control symbol. Datum reference letter entries need not be in alphabetical order. Where a single datum reference is established by multiple datum features, the datum reference letters are separated by a dash between letters. See Figure 35.

A composite feature control symbol is used where more than one tolerance of a given geometric characteristic applies to the same feature. A single entry of the geometric characteristic symbol is followed by each tolerance requirement, one above the other, separated by a horizontal line. See Figure 36.

Combined Feature Control and Datum Identifying Symbol. Where a feature is controlled by a positional or form tolerance and serves as datum feature, the feature control and datum identifying symbols are combined. See Figure 37. In such cases, the length of the frame for the datum identifying symbol may be either the same as that of the feature control symbol or 0.60 inch minimum.

Whenever a feature control symbol and datum identifying symbol are combined, datums included in the feature control symbol portion are not considered part of the datum identifying symbol. In the positional tolerance example, Figure 37, a feature is controlled for position (in relation to datums A and B) and identified as datum C. Whenever datum C is referenced elsewhere on the drawing, the reference applies to datum C, not to datums A and B.

Combined Feature Control and Projected Tolerance Zone Symbol. Where a positional or perpendicularity tolerance is specified as a projected tolerance zone, a frame containing the projected height followed by the appropriate symbol is placed beneath the feature control symbol. See Figure 38.

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FEATURE CONTROL SYMBOL PLACEMENT. The symbol is related to the considered feature by one of the following methods. (See Figure 39.):

    (a) Adding the symbol to a note or dimension pertaining to the feature.

    (b) Running a leader from the feature to the symbol.

    (c) Attaching a side, end, or corner of the symbol frame to an extension line from the feature.

    (d) Attaching a side or end of the symbol frame to the dimension line pertaining to the feature.

IDENTIFICATION OF TOLERANCE ZONE. Where the specified tolerance value represents the diameter of a cylindrical zone, the diameter symbol shall be included in the feature control symbol. Where the tolerance zone is other than a diameter, identification is unnecessary, and the specified tolerance value represents the distance between two parallel straight lines or planes, or the distance between two uniform boundaries, as the specific case may be. For roundness, cylindricity, or runout, the tolerance value shown shall represent the full indicator movement. If desired, the term TOTAL, WIDE ZONE, or ON RADIUS may be used to supplement the tolerance in the appropriate feature control symbol.

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TABULATED TOLERANCES. Where the tolerance in a feature control symbol is to be tabulated, the letter representing the tolerance is preceded by the abbreviation TOL, as shown in Figure 40.

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