Model Forum / General / Models / July 2006

I find even the steel bits break very easily, but the 1/8 shank carbide
ones REALLY break a lot. I have stopped buying them.  I find model expo
has good prices on three-packs, three bits of one size.  I consider
small drill bits expendable supplies.

You can get a pretty good selection of sets at
   www.drillbitcity.com

Just a satisfied customer.  I've bought mostly very, very small sizes there.
#81 down to #97 are available most of the time.  Larger sizes seem to be
always available.

   Norm

FYI, Those packs of 1/8" shank carbide drills sold by Micro Mark are
USED circuit board drills. I use to be involved in the manufacture of
military electronics. The machines they come off of are huge,
mulitiple spindle computer controlled router / drills. The secret is
that the RPM is extremely high, the feed rate into the material is
precisely controlled and there is NO play (wiggling) between the
spindle and the material being drilled. It's pretty difficult not to
snap them off when drilling by hand with a Dremel tool !

It is standard manufacturing practice to replace the drills after they
drill X number of holes. That's where Micro Mark is getting them and
why the sizes you get in the packs is pot-luck. There's still lots of
life left in them for the hobbist - they just too dull to reliably
make a good hole in a circuit board.

I bought a box of them from Micro Mark years ago and immediately sent
them back when I saw what they really were. (I recall they were
advertised as assorted carbide burrs at that time.) I stick with steel
drills. They are MUCH less likely to snap.

A couple of tips for drilling those #60 - #80 holes:

1) To keep your drill from skating all over creation, always start
your hole with an indentation from a sharp needle or pin. Your'll find
it a lot easier to get a non-moving object exactly where you want it.
The drill will self-center in the indentation. If you want holes in
straight row, lightly scribe a line, then prick with the pin. To get
even spacing, use saw teeth as a guide for the pin. Or use dividers to
"walk" down a scribed line.

2) Once you get the hole started, use a little lubricant to help the
chips to clear the flutes of the drill without clogging up. Nothing
exhotic. A little dish soap, candle wax, oil. Even spit is better than
drilling dry.

3) If the chips aren't clearing the drill, pull the drill out
immediately and wipe the chips off.

4) Drill at low RPM. Melting the plastic and binding the drill is the
biggest problem. Go slow, use lubricant. The lowest speed on the speed
controlled Dremels is OK for #60 down to #70. Smaller than that, I use
a foot operated speed controller which runs the flex shaft so slow I
can count the revolutions.

5) Use a pin vise and drill by hand. I find the standard double ended
pin vise too unstable to use with small drills, so I added a yoke to
the "big" end for my index finger. The yoke has a shaft that goes into
the untightened 1/8" collet. This allows me to hold the pin vise
steady with my index finger while turning the body of the vise with my
thumb and middle finger. This feature is common on many jewelers
screwdrivers, but I haven't seen it on a pin vise. It might exist.
I've tried the miniature Archimedes drill (which has a high angle
helix on the outside with a mating nut that you run up and down the
shaft to make it turn) but I cannot recommend it. I found it too
unstable.

6) A final tip. If you are having trouble - consider buying new
drills. Styrene is soft - but it is surprizingly abrasive. Ever notice
how often you replace your #11 blade? You may not use that #80 drill
often, but its cutting edges are a lot smaller. It wears out, too!

Greg Reynolds, IPMS