A 25 mill is a monster pcb mill if you are making high speed stuff.

I used 7 and 10 mill endmills that were typically 2 and one was a 3
cutter. They are carbide and turn fast - 10k or more and must fly cut
Copper and fiberglass and epoxy matrix (and other exotic materials).

Small pcb drills are often sold in Dremel kits. They have the large ring
on them.

Martin

On 12/2/2012 4:55 PM, Larry Jaques wrote:
On Sun, 02 Dec 2012 16:53:33 -0500, axolotl
wrote:

A coworker bought a view camera, and while searching for glass wants to
take some pinhole pictures. I ran through the formula, and the pinhole
needs to be about .025". I have, somewhere, PCB drill bits in that size
range. The material will be brass shim or soda can. My first attempt was
going to be taping the Dremel to the quill of the drill press and go for
it. Anyone have better ideas for a clean burr free hole?

Mill the hole, don't drill it. You should be able to find an end mill
that size fairly easily. I think I have one in the sets I got from
Gunner, complete with 1/4"(?) holders.

Otherwise, maybe use a drill press and drill it, flip it over, run a
chisel over the burr, flip it and drill; repeat until perfect.

Question: How do these mfgrs -make- bits that small, anyway?

--
...in order that a man may be happy, it is
necessary that he should not only be capable
of his work, but a good judge of his work.
-- John Ruskin