Hi Peter,
Well, from reading all the responses on this topic, I can see that there
are a lot of different approaches.  For what it's worth, I'll share what's
worked fairly well for me.

I use a Dremel tool with a #540 emery cut-off wheel.  It's about 1.25"
dia., and 0.0625" thick, so it leaves a nice, thin kerf.  I use the top
speed, about 30,000 rpm.  You can also use the smaller #409 wheel (15/16"
dia.).  It has an even smaller kerf, as it's only .025" thick.  It's
more fragile, so you need a gentle touch to avoid breaking it.

As someone else pointed out, the wheels often don't last very long.
Luckily, they're pretty inexpensive, and come in packages of 20 and 36.
 The trick to getting them to last is to be gentle, and sort of "skim"
where you want to cut.  Make a few passes, if necessary.  Unlike a conventional
saw, you don't want to force it.  Let the speed of the tool do the work,
and don't bog it down.  Always keep the cut-off wheel in a straight line
with your cut, ie. don't twist it.  It will break.  I don't go through
many wheels now that I've got the knack.

It's a good idea to clamp down your board, so you can use both hands
to guide the tool.  I usually work freehand, and then straighten out
the cut with a file, after I've photo-etched the PCB.

If I were making a lot of boards, I guess I might try to rig up some
sort of a jig to hold the Dremel, and get creative and clamp down some
guides to feed the board straight -- kind of like a mini-table saw.
When using presensitized boards, I put a piece of masking tape over the
line I'm going to cut.  This keeps the protective plastic backing stuff
from lifting at the edges and getting ragged.  It also helps keep the
photoresist material from chipping.  For sensitized boards, I think this
is better than scoring with a knife, since you don't apply any pressure
with the Dremel, which might damage the resist.

Obligatory safety precaution: DEFINATELY wear a good dust mask.  Glass
particles, and whatever other crap is in the PCB, is bad news for your
lungs.  Your body can't get rid of glass dust, since it's completely
inert.  I think the condition is called silicosis.  And of course, safety
glasses are mandatory when working with fragile cutoff wheels spinning
at 30,000 rpm.  You probably don't want a shard in your eye, and they
DO break from time to time.

Hope that's helpful,
Ray
Dremel Tool Shill

P.S.  If you guys play your cards right, I may even explain how to make
a suicidally dangerous "Dremel Tool Helicoptor".  Hint: have 9-1-1 on
your speed dial.

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