The add-on fixturing plate gives you lots of options that a bare faceplate
doesn't offer (without more drilling of the faceplate, anyway).
A thicker fixturing plate would provide more workholding alternatives
without extending the workpiece as far from the spindle bearing that a
full-sized chuck would likely cause.
I think the faceplate solution saved you a lot of grief as far as minimizing
the potential for chatter, by keeping the workpieces close to the headstock
bearing (especially since the lathe doesn't have variable speed).

Complexity and expense nearly always enter into the equation for
convenience, it seems.. but hey, it's for the enjoyment of metalworking.

I haven't used double-sided tape for workholding, although I've seen that
it's a fairly common method.. but I think I'd feel more confident with
mechanical fasteners retaining the workpiece.
For the ultimate in precision (typically not my goal), having the workpiece
securely seated on a (clean) metal surface would insure that the workpiece
is precisely flat against the fixture plate/reference surface.

I did notice your excellent safety bar approach.. inexpensive and practical.
A soft tip on the end would ensure that the bar doesn't affect the spindle's
internal taper, in the unlikely event of an Oh **** incident.

With other workholding methods, centering shouldn't be an issue with the
shoulder of the fixture plate recess to accurately center the rings,
otherwise, adding a disk/ring in the ring I.D. area for other fixture plates
may work well.

I don't recall at which stage of the process you're finishing the I.D. of
the rings.

--
WB
..........


wrote in message
...

I had a look at some of them. Firstly, only the smallest ones would
hold the ring without sticking up above the surface of the ring and
interfering with facing. Secondly, the smallest ones have only very
limited range of gripping. Thirdly, there is the issue of centering
the workpiece accurately.

In the end I was not sure that they would not do the job any
differently than a 4-jaw chuck. Plus they would add complexity and
cost to the existing project (e.g. I doubt that I could get away with
just a 1/4" aluminum plate).

I am keeping them in mind for a similar project in the future, though.

Michael Koblic,
Campbell River, BC