Th/qc54 Motor Controller Problem & Question

[WesPete66]

I finally got my TH/QC54 lathe dc motor conversion done, and up and running! I did some practice turning on a scrap piece and all seemed to work fine. Took into making my first actual part, a small shaft .390 diameter CD steel. I made a number of passes on the part, when the motor speed suddenly changes. It was ~ .12" along the shaft, just getting into the cut, when the speed drops down to about 1/3-1/2 what it was. I back out of the cut, turn the knob to zero then back up, and the speed comes back. until into a cut again..
I used an MC60 motor controller and a treadmill motor, and I suspect the controller is causing this (yes??). So is there some adjustment on this control board that allows it to cut back the motor speed at some given load? Is something else a likely cause?
Thanks in advance!
Wes

 

[markba633csi]

There should be a current limiting adjustment on the controller, it may even be marked on the board. I would try that first if you can identify that control. Can you post a close-up photo of the board?
Mark S.