I think that this is a simple question, but I don't know the answer. I
am sure that a die maker would know the answer, and probably other folks
as well.

I want to make a simple male and female die for forming sheet metal.
The sheet metal is 0.040 inch (1 mm) thick.

The male die would be a piece of 1/2 inch (13 mm) diameter round steel
rod bent into a 2 inch radius. The female die would be half round in
cross section, and will probably be made of UHMW plastic.

What I want is for the female die to fit the male die pretty well,
allowing for the thickness of the sheet metal. I was going to make the
female die by drilling a 9/16 inch diameter hole in a rectangular piece
of plastic, and then use a saw to cut right down the centerline of the
holes, leaving a half round form. But since the male die is a bent rod,
I would then need to sand or file the the female die to fit. But how do
I know where to sand, and how much?

One approach would be to pull a piece of shop cloth (strip of sandpaper)
between the two dies, and let the shop cloth remove the high spots in
the female die. If I use that approach, I don't need to know where the
high spots are. This would not result in a perfect fit unless the shop
cloth was the same thickness as the sheet metal being formed, but it
might be good enough. Perhaps I could use two or three thicknesses of
shop cloth to approximate the 0.040 inch (1 mm) sheet metal.

But if I want to use a sander or grinder or file to get the fit right,
how can I know where to remove material from the female die?

I do not have a mill or any machine tools other than a drill press.

Thanks in advance.

Richard




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