BLANK DIAMETER SELECTION
FOR CIRCULAR PITCH KNURLING WHEN KNURLING FROM THE "CROSS SLIDE".

The following formula can be used to determine an approximate blank diameter for proper tracking. This blank diameter can be adjusted for optimal results once good tracking has been established. It is advisable to do all test rolling at the same speed and feed as is planned for the production run.

Knurl Diameter [ideal] =
Blank Diameter / #Teeth [part] x #Teeth [die] - C.F.*

* C.F. = Tracking Correction Factor

This correction factor takes into account the fact that the tips of the knurl teeth have penetrated below the blank diameter by the end of the first revolution. Several other formulas can be derived to calculate almost any aspect that may be required. (For approximate C.F. values see Table II.)

#Teeth [part] = ( Blank Diameter x #Teeth [die] ) / ( Knurl Diameter + C.F. )

Blank Diameter = ( #Teeth [part] / #Teeth [die] ) x ( Knurl O.D. + C.F. )

The approximate tolerance for the knurl diameter should be:


± (.5) x (C.F.) x (Knurl Diameter / Blank Diameter)

If the finished diameter of the part is known, an approximate blank diameter can be determined by subtracting the proper value from Table I.


BLANK DIAMETER SELECTION
FOR DIAMETRAL PITCH KNURLING

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 ASA 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 Table III.)

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")

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 penetrates 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.