[KurtB]

Wow, Steve and Ray, that's a lot to digest, and that's just the kind of info I need, not being a coin cutter myself. I was daydreaming today while at work, and was thinking bronze would be a good choice. The material is not a big contributor to the cost, it is, like so much else in life, the labor involved.

Steel would be ideal if it were not for the rust issue. Stainless would be a good, durable choice, but it is always a bit trickier to machine than many other metals. The more I think about it, the more I like bronze. Soft enough to not mar or nick, yet durable, no rust, and it simply looks nice too.

Steve - if someone were to start with a $300 coin (and go UP from there!!) it'd make sense to invest in a holder that's machined purely for that coin. That would avoid two problems you mentioned - variations in diameter, and the thickness of the rim. Given a coin of known diameter (let's say it 0.8730"), you could make a double-ended fixture with the same diameter on each end, but with the only difference being one end completely recesses the coin below the rim of the collet for max holding power, and the other end raises the coin slightly proud of the collet, so you have access to the rim of the coin for light cuts. In either case, it could have the double-recess that would keep the reverse in zero or absolutely minimal contact with the collet, and that only on the area very, very close to the rim. The inner recess can probably be bored so that the only contact is the rim plus a hair's width extra, just enough to keep the coin from simply falling down into the fixture.

If a coin is badly out of round, there's not much you can do other than to scan it and use a CNC machine to pocket a collet device to the exact shape of the coin.

I'm not too concerned about the durability of the aluminum vs. mild steel, when it comes to the threads for the clamp bolt . Modern wrought aluminum alloys, especially 7075-T6, have yield strengths superior to that of mild steel. When properly threaded, with good, full threads, the head of that steel socket head screw will shear off of its body before stripping those threads. But I keep going back mentally to bronze. I just love bronze, both mechanically and aesthetically. There's an alloy called aluminum bronze (sounds weird, but it's great stuff) that is significantly harder and springier than a traditional copper/tin bronze alloy. That might be the ticket.

Both you and Ray mentioned the need for either a hex or square shape. I can easily see the advantages of that. I'll crank one up out of bronze and include a shape that would do what we seek.