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BigBoy1
08-02-2011, 02:14 PM
I need to straight knurl the outside of a 5/8" diameter part and I need the knurl ridges to be every 5 degees or 72 ridges on the outside diameter. The straight knurling tools are listed as having a pitch in threads per inch. To find the pitch of the straight knurling tool for my part I need to have 72 ridges for the circumfirance of 0.625" time 3.14 (Pi) or 72 / ( 0.625 x 3.14) = 36.7 pitch. There are 21 and 33 pitch straight knuring cutters so I should get the one with a 33 pitch as it is the closest to what I need. Is my figuring correct? Thanks.

TGTool
08-02-2011, 02:24 PM
If you actually need exactly 72 ridges on your part I don't think you can depend on the knurling tool to do that. You're likely to get somewhere in the range depending one how the tracking develops. If you're set on knurling you're likely to need to play with parameters a little, such as changing the initial diameter and changing the initial preload to get what you want. If the 5 degrees and 72 count is important you'll probably have to index and cut with a rotating cutter or a shaper-type operation.

Rosco-P
08-02-2011, 02:36 PM
You're making a straight knurl on the part? Coining it? Cut it like it was a spur gear, with a dividing head.

Al Messer
08-02-2011, 07:19 PM
If you had a Logan lathe like I have, the Bull gear has 72 teeth. Grind a "V" tool bit, mount it on its side and cut the "teeth" by racking the carriage back and forth, indexing with a chip of wood firmly held between each tooth on the Bullgear.

Al

SGW
08-02-2011, 09:38 PM
I've made a few straight-knurl knobs more or less the way Rosco-P and Al describe. It gives a nice result. The knobs were brass, and I planed out the grooves by hand with, I think, a 60 degree tool mounted in my unpowered and locked mill spindle. I cranked the X table direction to apply the cuts. If you want exactly 72 grooves 5 degrees apart, I think some form of that technique is the way to do it. Knurling is subject to too much randomness.