How Slim Can It Go?

Ron, since you can readily obtain 1"o.d. aluminum tubing in 0.015" wall thickness, it stands to reason that with careful centering and light cuts, you could go down to 0.005" or so. You'd have to bolster the chucked end, and you wouldn't be able to work with much overhang.

LLoyd

It all depends on what load you are going to apply to it. In pure numbers the Moment of inertia of a 1" solid rod is .0490874. A tube with a .5" ID it is .0460194 so you don't loose a lot. For a .75"ID it is .0335558 so you loose about a third For a .875" ID it is down to .0203133 so it is less than half as stiff.

You would pretty much have to put the 1"OD tubing inside a 1" ID pipe to do the machining.

You could bore the wall pretty thin if you held it in a 5C collet. The other end would need support, such as a wrapping of tape, to make it fit the collet closer tube.

jw