I have a problem.. Or, I'm not sure if it's a problem or not.

I have some limited experience with bowl turning (using my previous lathe, a few years ago), which makes me wonder if I do have a problem or not. But I want to consult some experts.

I bought a new (used) lathe a little over a year ago, but haven't been turning bowls until this weekend. Now that I've tried turning a few bowls using almost dry wood (has been drying for five years, but still feels a bit heavy), I do have some doubts. I meant to rough turn them, and let them dry for a while (I have a few such bowls already on the shelf since a couple of years, that I also mean to finish now).

I first turn the outside, mounted on a screw chuck (I have both a dedicated screw chuck that came with the machine, and a screw insert in my Sorby Patriot chuck). I have tried both screw chucks with the same result. When I have finished with the outside, I make a tenon for my chuck.

This is where the problem starts. When I remount the bowl on my chuck, no matter how carefully I adjust it, the newly turned outside of the bowl seems out of true. I realize this always happen to some degree, but it just seems like it's too much.

After I turn the inside, and remove the bowl, I can see that the rim of the bowl is visibly of different thickness depending on where you look. I haven't measured, but it looks like it's several millimeters off. Say 8 mm on one side of the bowl, and 5 mm on the opposite edge. The thickness is visibly different.

Is this normal? I don't remember this happening in the past. Not to this extent at least.

If it's not normal, I'd want to find the problem.

My suspicion is that it has do do with the chuck adaptor (which I had to have specially made for the spindle thread - Whitworth 1 1/4" if I remember correctly).

I have been checking things with a dial gauge, but can't come to a conclusion. It seems like the outside of the chuck is a bit off, but then, it isn't the outside that is gripping the bowl. I've tried measuring the jaws, but they have a small amount of play when not gripping anything, so I can't come to any conclusion there. Just now, an idea struck me.. Maybe obvious to others, but I should probably measure the jaws when gripping something, or maybe the object they are gripping.

A friend that used to work at a machine shop helped me make the adapter. He's retired and moved out of town since then, so I probably need to pay someone to make a new adapter. If it's really the adaptor that is the problem... It might as well be the chuck.. And if the chuck is bad, a new adaptor would not help. I would just be throwing my money away.

I've also been thinking of ordering a new chuck. Maybe a Vicmarc. But, as my spindle thread is unusual today, I can't buy an insert for any chuck. I'd still have to have one made for me.

Or could it be something else? Maybe the lathe itself? I haven't noticed any problems when turning chisel handles and such things, but that might not mean anything.

How would you investigate this? What to measure?

I can also add that I also have a metalworking, 4-jaw scroll chuck that came with the lathe. When checking the outside rim of this chuck with a dial gauge, it is actually only moving 0.01 mm when turning the chuck around. This feels like quality to me. I would like my other chuck to be as good. :-)

But, still, I'm not sure how much this means. I'm only measuring on the outside rim of the chucks. But it feels like an indication of where the problem is.