Homebrew PCBs

John,

I just went through this myself. It sounds like you have figured out what
you need. I ended up spending $60 on a nice selection based on what my
current circuit board needed.

Let me ask a related question - what do you have to drive them? Assume you
want to run at 200 surface feet per minute. Then the needed RPMs equals
200/(0.26 x D) where D is the diameter of the drill in inches. Given your
0.020" drill you are looking at 38,500 RPM which is about what a Dremel(r)
puts out. The mount must have very little side play because that can snap
these tiny drills too.

Rick

-----Original Message-----
From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
On Behalf Of thb201
Sent: Saturday, January 12, 2013 7:59 PM
To: Homebrew_PCBs@yahoogroups.com
Subject: [Homebrew_PCBs] What size drill bits?

I was looking to get some drill bits but I only want to get just a few
sizes, especially if I spring for the more expensive carbide types.  Just
out of curiosity, to get an idea, I measured the lead diameters of a wide
variety of components.  Surprisingly the diameters are all over the place -
everywhere from 0.016" up to 0.032" in increments of 0.001" for the most
common sized components.  I would like to stick to maybe just three sizes of
drill bits to (hopefully) cover most parts I'll come across.  I'm thinking
maybe 0.035" (#65 bit), 0.025" (#72 bit) and 0.020" (#76 bit) would cover
most eventualities.

Are these three sizes workable or am I limiting myself too much?  I don't do
a lot of PC boards so if I can keep down the number of sizes on hand this
would be a plus.

(I'm in Canada so I'm limited to what I can get here, usually from machine
tool suppliers like KBC.)

Cheers,
John



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