Tim Wescott fired this volley in
:

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.


Tim,
A "spur drill" comes to mind, but you don't have one. I might suggest
another way, without buying another tool (just yet).

Shorten your step drill. Just grind off the offending length. They're
not all that expensive, and you can keep the ground off version for
future "shallow-by-wide" drilling projects.

Use a cut-off wheel, or go VERY slowly on a grinder, cooling frequently
in water to avoid drawing the temper of the metal.

LLoyd


Lloyd