[choppero]

I have a customer that wants me to knurl a number of round knobs. I can make a holder for the part for the 4 jaw but I don't know if a knurling wheel will make an even knurl. Here is a picture of an original.

[rcs60]

i would say that the knurl you have pictured was done by a custom knurl wheel
#1 i would ask for a quote for a custom knurl
#2 (if you have to because you would have a problem generating a knurl that looked acceptable on a cnc lathe)
you could cut down the width of the knurl and generate the arc with the middle being comp'ed for the width you might get double knurling on either the start and finish or the middle of the part (because of the difference in dia.)

[Jim Dawson]

Looks like that could easily be done in a manual lathe with a standard knurling tool mounted in a radius turner. A little experimenting and practice would make it perfect.

You couldn't really properly do it in a CNC lathe without a B axis.

[choppero]

Hmm I was considering the radius tool holder. "Looks like it could be easily done" is different than "I did it with".But it's in the running. Thanks.

[Dualkit]

I have done quite a few things in 35 years of machining and done plenty of knurling, yet never on a radial surface. No idea of the size of that knurl and it honestly doesn't look very good. There are places that sell convex and concave knurls off the shelf. I would think radius turning on a manual machine would be difficult when you had to transition in the middle of the ball between using the front edge to the back. Probably doable on a CNC with some experimentation. This is one of those things where you have to decide if it is worth the risk. You could end up digging deeper in your pockets than you want and spending a lot of time on a solution while not be compensated adequately. The first thing I would try is radius turning with a knurl with almost a full radius on it, something shaped like a wheelbarrow tire, nice and round.

[choppero]

When I get the first part I'll know the radius. Colt made these knobs for the original Thompson 1928 SMG. And the replicas are highly sought after. I'll see if a custom Knurl is worth the pay. I don't even know the LPI of the original.