problems with chucks

[Hilel Salomon]

Help!! Anytime I am financially strapped, I solve the problem by an act of total denial. In this case, I decided to buy two lathes to supplement/replace my existing ones. One is a powermatic 3520B replacing my Vega and the other one, a nova dvr xp replacing/supplementing my Delta.
In Virginia, I spent most of my time making a sturdy table for the dvr xp. When I cut up some blanks (cedar/pawlonia/walnut) and did my usual thing-using a faceplate, roughing the shape and making either a dovetail for my axminster and nova chucks and a regular stub for my Oneway, I managed to break each one of the pieces at the chuck the minute I tried to hollow the piece.
I'd say it was the lathe, but when I got back to SC and tried the same procedure on my powermatic, the same thing happened twice. This didn't occur very often on my Vega (in SC) and on my Delta (VA). Can anyone tell me what's going on???

[Reed Gray]

It could be a number of things. Perhaps the 2 most important things are to have the proper depth, and then you must have enough shoulder (the flat on the bottom of the bowl to where it starts to curve up) to support the pressure. On a 16 inch diameter bowl, I like about 3/16 inch deep, and a shoulder perhaps 1 1/2 inch wide. For depth, I don't think that I ever use less than 1/8 inch, definately not 1/16, On a 3 inch diameter bowl, you can get away with a narrow shoulder, say 1/4 inch, even 1/8 inch. When you leave a narrow shoulder, you have to be more careful on how agressive you are on your roughing cuts. You can also over tighten the chuck. It needs to be snug, but don't crank down on it as hard as you possibly can. Softer woods can also crack with less pressure than harder woods.
Other than that, it is possible that your jaws aren't lined up properly, with one putting more pressure on the recess than the others.
robo hippy

[Hilel Salomon]

I have been tightening the chucks a good deal and I'll try not to. I wound up breaking off two cedar , one soft maple, one walnut, one cherry and one pawlonia bowl so it couldn't be the wood. I've had a Kelton hollowing jig sitting in the shelf unused and I may try that as well. Thanks for your advice and I'll let you know how it goes. Hilel.