Donut Chuck vs. Longworth

[jking]

There was mention on crokett's earlier post of making a donut chuck for finishing the bottoms of bowls. A donut chuck is easy to make, but, what centers the bowl? It seems you could spend a lot of time making adjustments to get the bowl centered in the chuck. Am I missing something?

What about a Longworth chuck? I had been trying to think of a way to make chuck that functioned like this when I ran across a reference to a Longworth chuck. I understand the donut chuck secures the work better, but, the Longworth self-centers. There are tradeoffs in most decisions, anyone have thoughts on pros and cons?

[Stytooner]

I would love to hear more about this with pictures and references.
I have a cnc lathe and a manual lathe. How to do the OTHER side has often perturbed me.

[gerti]

I built one some time ago and have used it a number of times:

http://gerd.knops.org/shopnotes/?p=13

[guycox]

I had pretty good luck with the doughnut chuck -- it's a lot easier to make -- I usually had a mark in the center of the bottom from where it was started between centers -- In any case, it's no big deal to put a dimple there when tenon is created to aide in the alignment in the doughnut chuck. I've moved up to a vacuum chuck (which you can also make - and it'll hold natural edge piece)..