Problem....

[Bonnie Campbell]

Okay, I'm not mechanically inclined... I was using my PSI Turncrafter PRO midi lathe this morning trying to turn out the cup on a goblet (first one and was really just practicing). And for some reason my Nova midi chuck kept working loose. Any ideas on what's wrong? Finally had to switch the chuck over to my palmgren to do the hollowing.

Thanks for any help!

[Patrick Taylor]

I have the Nova midi chuck on my Jet mini, but have not had any problems. Is the chuck coming loose from the spindle threads, or are the jaws coming loose from the piece?

[Bonnie Campbell]

It's coming loose from the spindle threads.

[Harvey M. Taylor]

Sounds to me like something is going backwards. With the threads going opposite the turning it should keep the chuck tight. Is there a set screw on the chuck to stop it from coming off? Does the lathe vibrate? It shouldnt, but that might cause your problem.

Yearning to do more turning.

[Neal Addy]

I was thinking the same thing, Max. The spin rotation alone should be holding it in place.

Makes me think we're not understanding the issue, maybe? Bonnie, when you say it is coming loose from the spindle during turning do you mean it is actually backing off the spindle threads?

[Patrick Taylor]

I've never had mine want to come off the spindle. Rather, the thread direction is such that each cut tightens the chuck on the spindle and I usually need the rods to get it off.

You're not outboard turning on the backside of the headstock, or turning "clockwise" are you? Assuming your threads are the right direction I have no idea what would cause that besides extreme vibration... and even then I can't really picture it.

I have had a heavy blank on a faceplate unscrew from the spindle, but that was due to the momentum of the blank while the spindle was stopping (when the lathe was being turned off).

[Bonnie Campbell]

Yes, it's backing off the spindle, especially when I shut down. If I don't hold my hand on the chuck it'd turn loose enough to hit the tool rest at the end. The chuck stayed on fine with the Palmgren. So I'm guessing it has something to do with the Turncrafter?

The lathe isn't vibrating. I'll go look at it more now. Had turned between centers to round the wood before mounting it in the chuck. Of course that didn't involve anything being screwed on....

[Ken Fitzgerald]

Bonnie.....if the chuck is coming loose from the spindle threads...I'd be concerned about 2 things.......1. Something with the spindle drive isn't working correctly...ie....is the drive belt slipping....motor stopping/starting/ running erratically?...2. Vibration but even if the vibration is happening, the direction of the spindle drive should be tightening and engaging the threads of the chuck.....JMHO....

[Ken Fitzgerald]

Bonnie to maybe clarify what I was trying to communicate....For the chuck to work it's way loose....you'd think the spindle has to be slowing or stopping so that the mass of the chuck and your turning allows them to continue turning faster than the spindle....thus the chuck backs off the threads.......I'd check belt tighteness......see if you can find something with the drive system that is slipping.....Good luck! Let us know what you find!

[George Tokarev]

Yes, it's backing off the spindle, especially when I shut down. If I don't hold my hand on the chuck it'd turn loose enough to hit the tool rest at the end. The chuck stayed on fine with the Palmgren. So I'm guessing it has something to do with the Turncrafter?

Could be. If the spindle is so long that it bottoms the adapter or the chuck without the rear of the chuck gaining extra friction by seating against the boss that shows in the illustration, you might have enough momentum to start an unwind. Or, if you've gone to a motor with electrical braking or have the belt too tight, could do the same. Even if you have electrical braking, a steady might provide enough drag to stop the unwind.

Try a 1" hole washer between the boss and the back of the chuck if you detect a gap. You can start with a simple pressed type, but if it's your problem, you'll want to go with a lapped type with uniform thickness.

[Ken Fitzgerald]

Excellent point George! I failed to remember about the friction you normally have with the shoulder of the chuck seating the the shoulder of the spindle! Excellent point!

[Tom Collins]

Perhaps this will end up as the stupidest comment in the Creek. I am not familiar with all the different lathes and their capabilities BUT, is this lathe reversable (I think some are) or does the belt have a twist in it causing the lathe to turn in reverse?

Tom C

[Corey Hallagan]

I use the PSI Turncrafter Pro and the Nova Midi chuck. I have never had this situation occur. This lathe is not reversable. If anything I have to take one of the bars to get my chuck off when done. Not sure why this would happen unless the spindle size of the chuck is not correct or something.

Corey

[Bonnie Campbell]

I'm thinking you're close to the mark George. There does appear to be a very slight gap between after screwing the chuck on tight. Though I've used the chuck before without any problem. Also I just turned another small thing on it using the chuck and it held?!?

I thought I had cleaned out the chuck threads before installing it the first time this morning, perhaps not well enough. I'm guessing that dust/chips could keep the chuck from tightening the way it ought to? So it made that slight gap worse than it'd accept?

No, it's not a reversible lathe. I did do a good check on the belt, it's in fine shape. Good point on things to check.

This is the first time I ever had the problem with it doing this (hopefully the last too!)

Maybe gremlins...... But I will get a washer to try on it. Thank you all!!! :)

[Bill Bolen]

Bonnie, I had much the same problem using my nova midi when I switched from my jet mini to a jet 1442. Seems the spindle shaft on the 1442 was about 3/8" longer (protruded more) than on the mini. I thought the chuck was bottoming out against the spindle shoulder bot on closer inspection there was a small gap between the spindle sholder and the chuck. Seems the chuck was bottoming out against the inside of the chuck jaws rather the the seat of the chuck. I cut out a pair of 1/4" vinyl washers from and old vinly fence post and slide them into place and then install the chuck, and now the chuck seats firm and no more unwinding of the chuck off of the spindle.. Hope this helps. ..bill

[Mark Pruitt]

For some reason, the same thing happened with a faceplate on my Delta Midi. I simply took my wrench, held the spindle with a tommy bar and tightened it. No more problems. That's the only time it's ever happened, and ordinarily I only have to hand-tighten the faceplate. You may be right about the gremlins.:eek:

[Curt Fuller]

Bonnie I've had the same thing happen while turning goblets. I'm no scientist but there's something in turning endgrain which causes a little chatter and the vibration hits just the right frequencey and the chuck actually starts to unscrew. There are two thing you can do to keep it from happening, actually three. You can put a nylon washer between the chuck and the spindle so it cinches down tight or you can give your chuck a good quick spin just as it's tightening down so it snaps against the spindle good and tight. And sometimes changing the speed that you're turning will change the frequency of vibration enough to keep it from happening. I turn quite a lot of goblets and I usually use a fortsner bit, about 1 1/4" or so, in a drill chuck in the tailstock to do the biggest part of the hollowing of the cup. Then you eliminate most of the chatter plus it's a little quicker.

[Bonnie Campbell]

Thanks for the tips Curt. I'll give the washer thing a try first then. I didn't think it was chattering much, being so small (3" height), but maybe that was just enough.

On another note.... is there a formula for cup size, stem length and base size? I'm going to try another tomorrow to see if the washer will hold it :) I definitely like the forstner bit tip ;)

[George Tokarev]

Bonnie I've had the same thing happen while turning goblets. I'm no scientist but there's something in turning endgrain which causes a little chatter and the vibration hits just the right frequencey and the chuck actually starts to unscrew.

Sounds like the first step in the scientific method to me - good observation. Perhaps http://hyperphysics.phy-astr.gsu.edu/hbase/tord.html this has some bearing?