Thread: Embarrassing screw up on motor RPM

With the helpful encouragement of the good folks here, I made a new end to a C face motor (either a 7.5 or 5 hp) with a 213 5TC frame - worked quite well. Bearing fit is perfect, oil seal, perfect fit on the gearbox etc. Sliding gear had a rather tapered bore so I carefully lapped it to perfection. The shaft was 1.375 dia and long enough so turned it down to be the internal shaft of the gearbox. A one part solution.

Then I run it after getting it all together and DANG, its 3200 rpm!


For some inexplicable reason i'd always believe it was 1750 but there was not motor plate and I didn't check it

Not sure if there's any way of pulling the chestnuts out of the fire on this one...from what I've read 1200-1800 rpm is what i want.....unless I find a near identical motor of the right RPM, then hopefully the new end is salvageable. Ultimately it will have a VFD driving it...but 3k is too fast to start with, right?

I regularly make finish cuts at close to 4000 rpms on 2" dia tool steels.
3200 would be good enough for me, dont run that fast all the time however.
Running topped out at less then 2000, would not be good for me, would lose the fine finish/accuracy ability.

3200 rpm had me scratching my head, isn't Canada 60 HZ? In any case, run it and try out, most likely you'll be pleased with its performance. You might end up using the backgear more often at lower speeds but that isn't a real problem. You also have the option of changing the pulley size(s) if required.

Originally Posted by DaveE907

3200 rpm had me scratching my head, isn't Canada 60 HZ? In any case, run it and try out, most likely you'll be pleased with its performance. You might end up using the backgear more often at lower speeds but that isn't a real problem. You also have the option of changing the pulley size(s) if required.

I was thinking of using a 3600 rpm motor as well.

thanks guys, you're making me feel better ....maybe i will continue down this path rather than look for another motor. It may well be that its a 7.5hp...seems more common for a 213 5t frame.

We're 60 hertz....3200 just came from a small handheld mechanical tach that I used - rubber wheel against the output shaft...I suppose its really 3600 but i dont' mess with motors enough to have realize that initially.

iirc, somewhere here I read the only difference between 4000 rpm models and 2500 rpm models was the motor speed, that the headstock and bearings are the same? Perhaps with a VFD and right pulley I can make it a 4,000 rpm model.