Rechucking wobble

[Democritus]

Hi Guys
I have a bowl I finished some time ago, but have always been a bit dissatisfied with it. I wanted to remodel the bowl interior, so today I put it back on my scroll chuck, and set about changing it. It went ok, but there was a very slight wobble as it rotated on the chuck. This didn’t affect turning the interior much, but did when I tried to texture the rim. I tried to adjust it, but couldn’t get it to run true. It was mounted using a mortise, and its base seems to be flat. It’s some time since I made the bowl, and wonder if it’s moved a bit over the last few months.
Does anyone have a method for sorting this sort of problem out?
D.

 

[Dalboy]

Check the outside measurements across the diameter in various places has the bowl moved because it still had some moisture content, If so the outside may need returning if the wall thickness allows

 

[Democritus]

Thanks, Dalboy,
I’ve checked the diameter at a number of points, and they all come out spot on 8 inches. I think the problem might be with the base of the mortise.
Anyway, it doesn’t look too bad, so I don’t think I’ll mess with it again.
I’ve attached a photo.

 

[Phil Pascoe]

I have a bowl (not made by me), sycamore, about 300mm with a 12mm wide rim. I looked to refinish it and I can't get a circle out of it. Wood moves.

 

[RickG]

The wood can have moved in all sorts of ways. I too have pieces I could make better if I could re-work them, but I just accept this as part of the journey. I'd do it better next time.

 

[Rorschach]

Wood movement will also cause a problem for re-chucking. a solid wood item will change shape pretty much every day by some amount depending on temperature, humidity etc. Add to that your chuck is not accurate, even the best scroll chucks have some inaccuracy so combine that with an item that changes it's dimensions and you will always have some trouble unfortunately. If you have a dial indicator you might be able to find the right combination of positions where most of the error is cancelled out, basically taking a leaf from a metal worker on a lathe, but this might be impossible with a wooden item.

 

[Mailman14]

I have a Clarke CWL 12D, and have had pretty much the same problem when turning pieces end for end.
Rough blank, made cylindrical, o.k. Tenon in tail stock end, o.k.
Swap the tail stock end for the chuck held end - part does not run true. About 1/8" variation from the tool rest to the piece. Tried rotating the wood in the chuck jaws and re-tightening, also knocking the wood to reduce the gap above the tool rest (does that make sense?)
So:- rotate the chuck with lightly held wood, until the wood touches the tool rest, which is loose in the tool post.
Mark this 'touching' area.
rotate one full revolution.
rotate, keeping an eye on the gap that forms.
Loosen chuck jaws, reduce gap to half of what is looks like. Re-tighten jaws.
Re-set tool rest to wood.
Rotate, repeat above.

Some of the time this will help. If it's not, then the wood may be 8" across, just not circular...

 

[Lazurus]

Ensure your tenon is not touching the bottom of the jaws.

 

[RickG]

As @Lazurus says, make sure the tennon has a good contact to the top face of the jaws. It shouldn't be touching the bottom of the jaws inside the chuck.