Measuring torque on lead screw

I am "working" on having a motorized feed for my lathe. The VFD control on my drill press is SO convenient that I think it would be nice on the lathe too. The biggest problem is getting the speed range, but I also needed to know how much torque is required, for motor sizing.

I have already extended the lead screw on the tailstock end, so I made an adapter that fits over that and has a 3/8" diam stub. I chucked the stub in a cordless drill, set the DOC worst case, started the lathe, then started the feed with the drill. As it was cutting I turned down the clutch on the cordless drill until it slipped. That setting being too small, I increased it one step.

I then took the drill and chucked up an L-shaped rod, with a 10" free leg. Putting the end of that leg on a scale, I very slowly pulled the trigger and noted the scale at the point the clutch slipped. It was 1 lb - 8 oz. Times the 10" arm gives 240 in-oz, or 15 in-lb torque. Surprisingly small!

Admittedly, this is not a very precise way to measure torque, but it's close enough for me. I'll probably double it when I come to chose the motor needed, just to be conservative. YMMV.

Bob

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Bob Engelhardt
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