Curved Knurling

Sb--ah! OK. I thought that was the price for the commercially available ones in the other link.
 
I have a couple of small concave knurls (for producing convex parts); you only need one knurl to do this work, at least in the sizes that I have; you also need to make a form tool to pre shape the work to the proper radius before knurling.
 
Thinking about it, couldn't a small tap be used to hob a 'knurl' from drill rod?
You wouldn't have straight knurl due to helix angle but I'm pretty sure it would look OK and be way easier to make?
 
Thinking about it, couldn't a small tap be used to hob a 'knurl' from drill rod?
You wouldn't have straight knurl due to helix angle but I'm pretty sure it would look OK and be way easier to make?
Unfortunately, machine screw taps have no relief on the body of the tap, the only relief is on the chamfer. Pipe and acme taps are the only ones that occour to me that have relief on the body.
 
I bought a box of knurls at a auction a while back that had several of this type
 
i have described how to make concave knurls before. I just run the blank wheel against a tap that is rotating in the lathe. The concave surface of your knurl blank must pretty well match the size of the knurl at its diameter at the tips of the teeth,or you ill get a messed up knurl. I make them from 01 or W1 drill rod,and harden after completion. Draw the color to a dark brown or purple.

By tilting the blank knurl blank,you can make the rope knurl type of knurl. I use a round ended knurl holder that I make,so it can be tilted in the tool post holder. I can get away with about 20º tilt towards the right. Too much tilting,and the knurl will start getting "serrated" by the back side of the tap's teeth. Tilt the knurl wheel a LITTLE bit back towards the left,and you can make the knurl grooves perfectly vertical. Otherwise,the knurl grooves will have a bit of tilt to them,as if they were threads,since taps do cut threads,of course,and the threads do have a bit of tilt so they'll screw into a hole ! I hope you can make sense of my rather poor description.
 
Hi George, I guess if anyone's trigonometry is up to snuff it would be simple to work out correct helix angle?
As you've done this and described it, is it possible to use next size down tap on a larger concave radius so it will cut 'straight' grooves? (because blank is tilted the 'curve' will be 'smaller' than 'correct' core diameter)
 
Tilted backwards a few degrees works perfectly. No need to get more complicated. It is still close enough to the groove in the knurl blank to work just fine.

I forgot to mention,MSC co. sells convex knurls that you can use as the "mother knurl". They only come in one size of convexity,but different pitches are offered from coarse to fine. They aren't real cheap(abt. $35.00 IIRC). I bought one and it worked just fine,but I prefer to make different knurl concavities by using the taps. I expect the convex knurls are really for making long knurled surfaces by feeding them along a straight rod or cylinder.
 
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