These pics are of one I made for adornments that go on a 9/16" tenon. This first pic shows the face profile:
Basically I turned the aluminum stock to a precision (not quite snug) fit to stock drilled with my 9/16" bit, then filed a flat on one side. If you have a milling machine, you can use that, but it only took me a couple minutes to file the flat. It should be only deep enough to fit a 1/16" pin once your adornment is mounted. This photo is of some drilled ivory mounted on the pin chuck where you can see the pin inserted into the flat:
Without the adornment mounted, it looks like this:
Yes, I did indeed lose that pin twice while setting up that shot.
Once you've got the chuck made, mount your adornment and tighten it by turning it clockwise. The pin will wedge itself against the inside diameter of your material and the flat filed in the tenon, and it will hold it securely and concentric with the ID. Obviously a collet chuck like the one I'm using here will make things easier and more accurate, but for pipes they're not strictly necessary. Once it's tightened down you can face your adornment:
Or even turn it round:
A pin chuck is a crazy simple tool to make (even on a wood lathe), and worth all kinds of time savings. Aluminum is what I use, since it's inexpensive, but any metal can be used. The pin is just a piece of 1/16" drill rod stock, but you could use the shank of a broken drill bit instead.
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