Hey Tim,

i have not read "down" my list here, so maybe you have better
suggestions already, but:
Get somewthing, a flat washer perhaps, with a hole in it the size you
want. Tape it to the tank so it is rigid temporarily. Poke a
smallish hole in the tank, and then run a Dremel stone around and
around until you are "tracing" the inside of the "washer".

Problen will be cleaning the "swarf" out the tank then.

Good luck. Let us know how you fare at the "contest"?

Brian Lawson,
Bothwell, Ontario.
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On Wed, 18 Apr 2012 16:49:31 -0500, Tim Wescott
wrote:

I've got a little 3oz fuel tank (model airplane) made out of thin
tinplate (a Dole Pineapple Chunk can, actually). So, maybe about 10 or
15mil, with corrugations.

I need to drill a 1/2" diameter hole in it, to solder in a fitting. I
know that if I use a regular 1/2" twist drill I'll just rip out big hunks
of tin -- so that's a no-go.

This is a last-minute rework to get me to a contest this weekend, and
I've spent out the modeling budget this month. So I'd like to be able to
do it with tools I have in the shop rather than spending time or money I
don't have to order something, or even nip around to Horror Freight.

I have a nice stepped drill that goes up to 1/2 inch, but it's longer
than the tank. I may just go ahead and drill through and patch up the
far end -- but if there's a better solution, I'm open to suggestions.