Powermatic Lathe Spindle Pulley Moving Mystery

Woodshop
#1

Twice in the last three weeks, I used the powermatic lathe and noticed an odd rumbling/rubbing sound, like a bearing was bad. It was not very loud - but something was not right. Long story short - the pulley on the spindle had moved about 1/2" to the right the first time and 1/8" to the right the second time. The drive pulley and the spindle pulley were not vertically aligned. The belt was on but “tilted”. I checked the set screws that are supposed to keep the pulley from moving horizontally and they were very tight. Hmmmmmmmm… The key between the spindle and the spindle pulley was there - it had not fallen out.

It’s an easy fix - loosen the set screws, move the spindle pulley left so it is aligned with the drive pulley. Then retighten the set screws. Noise goes away.

Any thoughts/insights on why this might be happening? How to prevent it in the future? It did notice that the lathe was in “reverse” mode on both occasions - this may or may not be related to the pulley moving horizontally.

#2

Hey Dan, I was using the Powermatic yesterday afternoon and left it in reverse - my bad, I’ll try to be more careful in the future. I did not notice any odd noises, no idea what might be going on.

#3

Nothing wrong with leaving it in reverse. Although you might freak out a new wood turner who doesn’t realize it’s in reverse.

However, it is not a good idea to run a lathe with a chuck in reverse without tightening the set screws that hold the chuck to the spindle. Without tightening the set screws, the chuck can (and does) back out of the spindle. The bowl (or whatever you are turning) will become wobbly. In extreme cases the chuck and bowl will come off and go flying. I’ve been there, done that - but fortunately the chuck did not completely come off.

No need to tighten the set screws when the lathe is in ‘forward’.

I would ask that if you do use reverse and tighten the chuck’s set screws that you untighten them. The next user might not realize the set screws are tight and use a lot of force to remove the chuck - this will strip the spindle threads.

You are probably thinking that no one would ever remove a chuck with tight set screws - it takes a lot of force to do so (like you need additional leverage/cheater bar/vice grips to do it). But it has happened twice in the last 5 years at the Makerspace. Once five years ago on the Powermatic and recently on a Jet. In both cases the spindle threads were stripped and the spindle had to be replaced. Spindles are $250 for a powermatic and $113 for a Jet.