# Diametral Pitch Knurling & Conversions

## BLANK DIAMETER SELECTION FOR DIAMETRAL PITCH KNURLING DIES

Blank diameters for diametral pitch knurling dies are more easily computed, since they are always common fractional sizes. The formula is as follows:

Blank Diameter = ( #Teeth [part] / Diametral Pitch )

American Standard ANSI B94.6-1984 describes the diametral pitch knurl system. Diametral pitch knurls are designed to track uniformly on fractional size stock up to 1" in multiples of 1/32" or 1/64". They are held to closer tolerances for this purpose.

The American Standard recommends that the use of 64 Diametral Pitch knurls be avoided as much as possible, and that preference be given to the use of 96 D.P. knurls for simplification of tooling. (For Equivalent Normal Circular TPI see below.)

The number of teeth that will be rolled can be easily determined by multiplying the blank diameter by the Diametral Pitch of the knurl. Example: A 96 D.P. knurl will roll 96 x 1/2 = 48 teeth on a 1/2" diameter stock.

 D.P. Blank Diameters for Uniform Tracking 64 every 1/64" 96 every 1/32" (also every 1/96") 128 every 1/64" (also every 1/128") 160 every 1/32" (also every 1/160")

 D.P. Equivalent Normal Circular TPI Straight Teeth 30° Diagonal 64 20.7 23.9 96 30.8 35.6 128 41.1 47.4 160 51.2 59.1

NOTE: Unfortunately the above formulas do not hold precisely for all conditions. Sometimes apparently identical knurls from different manufacturers will not track on the same blank diameters due to a difference in the sharpness of the teeth. Also, it is possible for the number of teeth rolled on a part to change as the knurling tool wears. How deeply the knurl penetrates into the work blank on the first revolution is the main factor in determining if an adjustment should be made to the basic formula.

Some factors which affect this penetration are:

1. In-feed rate (or axial feed rate for knurling from the turret)
2. Sharpness of the knurl teeth
3. Hardness of the material
4. Included tooth angle of the knurl (a sharper angle pentrates easier)
5. Width of knurl face (a narrow face penetrates easier)
6. Method of knurling (bump from cross-slide or end knurling from turret)
7. Bevels on edges of part or knurl tool (affects knurl penetration from end)

A change in any of the above variable may correct (or cause) a mis-tracking problem.

Table I. ANSI Standard Preferred Sizes for Cylindrical Type Knurls*
Nomial Outside Diameter
D
Width
of Face
F
Diameter
of Hole
A
Standard Diametral Pitches, P
64 96* 128 160
Number of Teeth, N
for Standard Pitches
1/2" 3/16" 3/16" 32 48 64 80
5/8" 1/4" 1/4" 40 60 80 100
3/4" 3/8" 1/4" 48 72 96 120
7/8" 3/8" 1/4" 56 84 112 140
Additional Sizes for Bench and Engine Lathe Tool Holders
5/8" 5/16" 7/32" 40 60 80 100
3/4" 5/8" 1/4" 48 72 96 120
1" 3/8" 5/16" 64 96 128 160
 *The 96 diametral pitch knurl should be given preferences in the interest of tool simplification. Dimension D, F, and A are in inches.

Table II. ANSI Standard Specifications for Cylindrical Knurls with Straight of Diagonal Teeth*
Diametral
Pitch, P
Nominal Diameter, D
1/2" 5/8" 3/4" 7/8" 1"

Major Diameter of Knurl (Inches), D+0.0000, -0.0015

64 0.4932 0.6165 0.7398 0.8631 0.9864
96 0.4960 0.6200 0.7440 0.8680 0.9920
128 0.4972 0.6215 0.7458 0.8701 0.9944
160 0.4976 0.6220 0.7464 0.8708 0.9952
 All dimensions except diametral pitch are in inches. Appropriate angle of space between sides of adjacent teeth for both straight and diagonal teeth is 80°. The permissible eccentricity of teeth for all knurls is 0.002 inch maximum (total indicator reading). Number of teeth in a knurl equals diamtral pitch multiplied by nominal diameter. *Diagonal teeth have 30° helix angle