Hi Don, pattern fitting, which is what this really is, is a prehistoric method. I wouldn't mind a set of telescopic gauges, though.
Today I dug out of the depths of my tiny shop my treadmill motor and DC controller -- a "Cycletrol 150." Both bought used 3 years ago on Ebay. Both subjected to way too much moisture. I had my doubts they would work.
After finding a schematic and manual online, I tried for hours to get that motor to turn, but no luck. There were 8 DIP switches, 3 potentiometers on board and lots of screw terminals with inputs and jumpers. Nothing worked. The schematic called for a 5K ohm external pot, for the speed control, and I had squirreled away a linear I had bought for this purpose from Radio Shack before it closed. That's how old all this stuff is.
(Cyclotrol Model 15303 Manual attached below)
One obvious problem was that the red "Brake" LED was always on. I tried everything, and was about to give up, when I tried just disconnecting the 5K pot altogether. Suddenly the motor ran. I tested the pot -- it was fine, double checked my jumper wires...they were fine. Finally I tried the only other pot I could find in my electronic junk box, a 1 megohm type. Oddly enough, it worked -- after a fashion. The motor would start, and I had some control over speed.
I started to play with the onboard trim pots -- one adjusted the minimum motor speed, and one adjusted the maximum. With these I was able to adjust a full range of RPM for the speed pot. So all was working finally. Only spent all day on it! No further work on the lathe
But I really don't understand why the 5K pot the mfr. called for didn't work, while a 1 megohm pot did. I mean how could it be that far off??? I substituted back the 5K ohm pot, and the same problem returned. I even found a 10K pot in an unused piece of computer gear, pulled that out, tried it with the speed controller and again, no go.
Well, I guess I ought to just be happy it works finally. It's just a puzzle to me. But onward with the lathe.