DeepDiver wrote:
"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

Firstly it probably isn't really necessary to harden if you are only
drilling a few pieces in brass.
If you are making a bazillion parts it would probably be better to purchase
a bit specifically for the purpose.
I have the impression that oil hrdening drill rod is less prone to warping.
I'm no expert on this so best ask around for better informed opinions.
Technique is important when hardening to avoid distortion.
Done correctly I would suggest you can keep the tolerance within a few
tenths.
Drawing the temper should pose no problems.
Instructions for doing all this are available in many places.

Regards.
Ken.