Machinery's Handbook, 31st Edition
1060 Knurls and Knurling Recommended Tolerances on Knurled Outside Diameters.— The recommended appli- cations of the tolerance classes shown in Table 4 are as follows: Class I: Tolerances in this classification may be applied to straight, diagonal and raised diamond knurling where the knurled outside diameter of the work need not be held to close dimensional tolerances. Such applications include knurling for decorative effect, grip on thumb screws, and inserts for moldings and castings. Class II: Tolerances in this classification may be applied to straight knurling only and are recommended for applications requiring closer dimensional control of the knurled outside diameter than provided for by Class I tolerances. Class III: Tolerances in this classification may be applied to straight knurling only and are recommended for applications requiring closest possible dimensional control of the knurled outside diameter. Such applications include knurling for close fits. Note: The width of the knurling should not exceed the diameter of the blank, and knurl ing wider than the knurling tool cannot be produced unless the knurl starts at the end of the work. Marking on Knurls and Dies.— Each knurl and die should be marked as follows: a. when straight to indicate its diametral pitch; b. when diagonal, to indicate its diametral pitch, helix angle, and hand of angle. Concave Knurls.— The radius of a concave knurl should not be the same as the radius of the piece to be knurled. If the knurl and the work are of the same radius, the material compressed by the knurl will be forced down on the shoulder D and spoil the appearance of the work. A design of concave knurl is shown in the accompanying illustration, and all the important dimensions are designated by letters. To find these dimensions, the pitch of the knurl required must be known, and also, approximately, the throat diameter B . This diameter must suit the knurl holder used and be such that the circumference contains an even number of teeth with the required pitch. When these dimensions have been decided upon, all the other unknown factors can be found by the following formulas: Let R = radius of piece to be knurled; r = radius of concave part of knurl; C = radius of cutter or hob for cutting the teeth in the knurl; B = diameter over concave part of knurl (throat diameter); A = outside diameter of knurl; d = depth of tooth in knurl; P = pitch of knurl (number of teeth per inch circumference); p = circular pitch of knurl; then r = R + 1 ⁄ 2 d ; C = r + d ; A = B + 2 r - (3 d + 0.010 inch); and d = 0.5 × p × cot a /2, where a is the included angle of the teeth.
As the depth of the tooth is usually very slight, the throat diameter B will be accurate enough for all practical purposes for calculating the pitch, and it is not necessary to take into con- sideration the pitch circle. For example, assume that the pitch of a knurl is 32, that the throat di- ameter B is 0.5561 inch, that the radius R of the piece to be knurled is 1 ⁄ 16 inch, and that the angle of the teeth is 90 degrees; find the dimensions of the knurl. Using the notation given: d 0.5 0.03125 cot45 0.0156 inch # # ° = =
C
d
A
B
r
D
p P 1 r 16 1
32 1 0.03125 inch
= = =
2 0.0156 0.0703 inch C 0.0703 0.0156 0.0859 inch = = + =
= +
A 0.5561 0.1406 0.0468 0.010 0.6399 inch = + − + = ^ h
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