I have been toying for a while with building a circle cutter to mount on the same burning table I have my old Airco Cam-o-graph pattern cutter mounted to.
Well it all suddenly fell together. Kind of like my positioner project last winter. A confluence of stuff with a few added bits.
The challenge is to rotate a cutting torch at variable speed over a burning table. The entire unit also has to swing out of the way of the pattern cutter.
I had a variable speed gear motor and controller from an old L-Tec wire feeder. I used a 5/8" lovejoy coupling to attach that to a worm gear box that has a 7/8" output shaft. Because the input shaft on the gear box is a bit bent, I mounted the motor in a rubber soft mount, so it can wiggle. The lovejoy coupling makes it run smooth despite the bent shaft.
I have it mounted so the output shaft points down. I used a rigid shaft coupler to attach a 7/8"D x 36" bar to the output shaft. I already had a machine torch with a fancy mount and a rack and pinion gear for adjustment. All I had to do was make a mount for the rack bar to go horizontal from the lower end of the 7/8" bar.
You can see a video of it at the dropbox