Could someone explain how they make an expanded shell?

Let's see...

Take a real coin...put it on a milling machine and take out all of one side (Heads or Tails)of the coin, excluding the thickness required to retain the opposite facing and the milled edge...the edge is then worked outward, from center, far enough to allow a like coin to nest within.

That's the bare bones!

Cheers!

I think you have those two actions reversed. You start by expanding the coin in a press. Then you move to the lathe. You need a step collet that fits the expanded coin. Then using a cutting tool ground for inside cutting you begin making cuts from the center out until you approach the correct depth and diameter. Make the final cuts very light to account for tool "push-off". Deburr the shell edge and you're done.
Bob

Wouldn't be the first time Bob! This could be a tomatoes / tomatos thing. I'm sure our resident gaffers will check in soon!

Cheers!

Okay that helps me! I was getting ugly face deformities form the cutting tool in my shop! Perhaps a smaller collet, instead of the single size! and i will try the press part first, my cutter fits the coin
e x a c t l y, so little room for error there!

Mwua ha haaaa!

Actually, he had the order right. I have a friend who makes expanded shells. You start off by milling out the inside of a regular non-gaffed coin. This requires a special fixture that has an inset plunger to pop the coin out of the holder, which is basically a collar. The coin is held in he collar with dopping wax.

Next, you have a series of slightly larger collars, each of which allows you to expand the coin a little more. The first is about .020 inch larger than the OD of the coin. The second is about .020 inch larger than the first one, etc. You gradually expand the coin by pushing the metal outward from the inside of the coin. When you finally have it almost ready, you knurl the outside edge of the coin and then do the final milling on the inside.

If you start by using pressure to expand the coin and stretch it out, it flattens the face of the coin. There may be some makers who do this, but it's not the recommended method.

Thanks for the vindication Bill!

Cheers!