My guess is that you used the center punch set to a much higher impact
than I do. Is yours adjustable? Mine makes a just barely visible
mark, so that my pads are accurately located. Those small drills need
very little dimple to center accurately.
John, you are probably right about the high impact force.
That was over 15 years ago, and I don't know what the
guys in that shop are using now. I never liked that punch;
maybe that was why. I prefer to use a sharp tool (scratch
awl) and tap gently with a carefully selected stick. (I have
a favorite that's perfectly balanced. ;-) The awl has a long
slender tip that makes it easier to see the work, whereas
the auto-punch had a fat squatty barrel. I may give
your method a try again on my next board; but after so many
years it may be tough to retrain myself!
The other advantage of the top-drill method is that you
can work from a single top-view layout and punch through
it onto the top of the board. I often make simple little
boards by drawing the layout on graph paper, and this
way I don't need any fancy see-through mylar film.
(Of course, I do need to get a back-side view when I'm
inking, and I use a light box for that.)
One more note: You mention small drills. I haven't used
a small drill on a circuit board in nearly 30 years. A ball-tip
carbide dental bur will *never* break from a side load, whereas
the standard carbide drills will snap if you look at them funny.
I use dental burs in a Dremel, and you can use the same
tip to carve slots and cut traces. In all those years, the
only ones that have needed replacement were those where
the shank bent when the Dremel fell off the bench and landed
on the business end. I now have a metal cap I slip over the
tool when I set it on the bench. End of problem. And these
burs were pretty cheap, too, from the local dental supply house.
Since I haven't needed to visit them in 20 years, I don't know
any current prices, but the originals were about the same as
single carbide drill bits, a couple of bucks back then.
And, true, they don't need much of a dimple to center. You can
zip along at about 1-2 seconds per hole. The only drawback is
that the taper leading up to the ball tip means you can't do stacks
of boards for production.
</evangelizing>
Bob Masta
dqatechATdaqartaDOTcom
D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com