Here's my finished test piece:
It's an old time style knob with a convex rope knurl.
I'd been thinking about giving it a try for some time, and this weekend I decided to go for it.
I started by making a small end mill that would make a ninety degree V-cut, for which I turned a profile on the end of a piece of W-1 drill rod I had in the scrap drawer:
Then, I chucked the piece in my little spin index and milled four cutting faces:
It's bit hard to see in the photo, but I simply forgot what I was doing and accidentally made a left handed cutter. No biggie, I suppose, since my mill runs in both directions. I heated the end of my cutter to a nice dull red and quenched it in water. Since I wasn't making a real production tool, I skipped the tempering process and left it "file-hard." I sharpened the teeth and gave them a bit of clearance with a diamond coated pocket hone:
Then I set up my spin index at a 30 degree angle and took successive cuts around the perimeter of a piece of O-1 steel, also from my scrap drawer:
I got the cutter running right on center and settled on 72 divisions. After the first go round, I noticed that there were a lot of burs, so I went around and recut each notch a second time. It took a while, but I got a nice even result:
After drilling and reaming a 1/4" hole, I contoured the piece a bit and parted off:
A quick trip on with a wire brush gave me a nice looking little knurl:
I gave it the same simple heat treatment - dull red and quenched in oil.
This time I followed the heat treatment with a one-hour tempering in the kitchen oven at 400 degrees Fahrenheit.
For my first trial piece I chucked up a piece of 7/8 inch diameter brass, turned a rough collar and plunged the knurl in good and hard mounted in a home made simple holder:
Just to complete the test, I used my lathe tool rest and a couple of wood turning chisels to finish off the contour of the knob:
Back to Machining Index