"Ken Davey" wrote in message
...

Others have mentioned using a reamer to achieve an accurate hole.
I would suggest a 'D' bit for final dimensioning. They are rather easy to
make and produce precision results.
Use a twist drill out to a few thou (or next drill under - it is not that
critical, specially in brass) under required size and finish with the D
bit.
A really simple type of D bit is a piece of drill rod of the required size
with one end cut off at a 45 degree angle. File, grind and polish the
angle flat to the best finish you can achieve - then harden and temper.
That's it. No relief or other fancy stuff.

I'm curious about the "harden & temper" part. First, what type of drill rod
steel do you recommend? Second, since this is to be a precision tool
(substitute for a reamer), then how do you harden without risk of
distortion? (Assuming that a heat treat furnace is not available.)

- Michael