Knurling -- how does it work?

[cnczoner]

In general, I know that the knurling wheel pressing against the material being knurled, and imprints the pattern. I expect that it would have to go through several passes to get a proper pattern marked on. But wouldn't the circumference of the material being knurled have to be an exact multiple of the pitch of the knurls/teeth? If not, I expect that after the first pass, the pattern would be offset a tad, then again on the next pass, messing up the pattern. Or does this happen on one pass? Or does the teeth of the knurling tool "jump" into the slight recess created on the first pass, etc?

Also, I expect that the knurling teeth have to be "tightened" does as the knurl marks are being made, to compensate for the lower depth of the partial marks already made... correct?

BTW, how fast is the material supposed to be spun for knurling?

Thanks,
-Neil.

[Geof]

Good grief, so many questions.

Last one first: Not as fast as for machining, I would use about 1/5 or less of the speed I machine at, sometimes slower. Knurls generally run on hardened steel shafts with no bearings and they often spin much faster than the work. I have found the speed limit is often avoiding getting the knurls too hot.

I have no idea if there is any fancy technical explanation for how knurls work and I have had them make a perfect knurl on one part and then a sort off half pitch knurl on another. What I found was the best approach was to feed in fast and then the knurl does seem to 'jump' into a good engagement; feeding slowly seemed to accentuate the double knurl effect.

[cnczoner]

Originally Posted by Geof Good grief, so many questions.

Which is what keeps this forum alive.

Last one first: Not as fast as for machining, I would use about 1/5 or less of the speed I machine at, sometimes slower. Knurls generally run on hardened steel shafts with no bearings and they often spin much faster than the work. I have found the speed limit is often avoiding getting the knurls too hot. I have no idea if there is any fancy technical explanation for how knurls work and I have had them make a perfect knurl on one part and then a sort off half pitch knurl on another. What I found was the best approach was to feed in fast and then the knurl does seem to 'jump' into a good engagement; feeding slowly seemed to accentuate the double knurl effect.

I don't have one (yet). It was just a curiousity, but maybe I'll pick one up to experiment with.

Cheers,
-Neil.

[spoiledbrat]

Fancy technical term is "forming process".

So much good info on this forum. Love it!!!

[kawazuki]

Have a look at the MIT shop video's - one of the lathe ones has a full explaination and demo of correct & incorrect operation

[wildwestpat]

Hi Neil

Yes for quick no messing resulta the diameter of the part to get the knurl has to be right so that the depth of knurl is formed to it full depth and there is no ghost knurl. The tool is turned into the work rapidly and as Geof describes it just snaps to a nice pattern from and absolute mess of lines. As the feed is very heavy the use of scissor type knurl tools can help. Also if the knurl can accomodate it run the tool into the work at a slight angle and traverse the tool slowly building up the pattern as the tool progresses down the length of the work - requires a bit of practice - use lube and keep the part and tool clean.

IMO firm incremental feed -slow speed - plenty of lubricant - keep the working face clean to stop imprinting swarf!

Regards - Pat

[cnczoner]

Originally Posted by wildwestpat ... ... keep the working face clean to stop imprinting swarf! Regards - Pat

Wow, never even thought of that. Good info folks, thanks!

[ckirchen]

Here's a post I made a while back that might help:
http://www.cnczone.com/forums/showpo...32&postcount=4

Chris Kirchen

[Crashmaster]

A little late to the game. I found this article helpful as well...

http://www.proshoppublishing.com/art...knurling.html#

[MadMax]

I used to believe the "tooth multiples" rule until I got lazy and munged knurls into any given diameter I felt like on my manual lathe. There doesn't seem to be a need to knurl on any particular diameters. I think what happens is that the kurls end up mushing a pitch diameter which is a multiple of the knurl pitch instead of starting their run at a round number. I do note that when diamond knurling, I often get a slight lead on the peaks of the diamond pattern. If one were to draw lines connecting the diamond tips in the axial direction of the part, you'd find that you'd transcribe gentle helixs around the part exterior. This "lead" on diamond knurling points leads me to think that there's some sort of self swaging pattern "fit" going on.

Start your knurl aggressively as Geof recommends. This prevents a skip knurl which ends up doing a double hit pattern. Work at a slow surface speed so as to not overheat the knurling wheels at the axles. Blow out fine swarf from the knurl axles periodically. I like to drip in a drop of heavy oil into the axles from time to time.