Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

I uploaded a picture of my laptop drill press to the photos section.

Mr. Moderator, maybe you can move that picture, and the following
text, to the files section. (I couldn't upload to the files section.)

The drill press shown in LaptopDrillPress.JPG was built for drilling
small PC boards. Total cost was less than $100 and it was built in
an afternoon.

I thought a lot about how to aim the drill accurately. I tried
mounting a rifle scope to the front of a Delta drill press with a 10
inch throat. That didn't work very well because there wasn't much
magnification obtained from the scope, and because it was hard to
judge the position front-to-back where the drill would land.

My conclusion was that the cheapest/best aiming solution was just to
be able to get my face up close to the axis of the drill bit and be
able to easily move my head around to view from different angles.
So I built the device shown in the picture.

The black platform is cut out from a 5-inch floppy disk carrying
case. The main reason for using that was that it provided a plastic
hinge that bends in one axis without any play/slop/unwanted movement
in other axes. The platform can twist (become non-planar) a little
bit, but that doesn't cause enough of a problem to bother fixing.
If necessary, the platform could be stiffened by glueing a board
underneath it.

The drill motor is a battery operated Craftsman. The gray plastic
band that holds the drill onto the wooden arm is a conduit mounting
strap, a molded plastic part used to attach electrical conduits to
walls or ceilings. A drill press with a hole saw was used to drill
out a semi-cylindrical cavity on the end of the wooden bar, to hold
the drill motor.

To use the drill press, I put it in my lap, hold and position the
PCB on the platform with my thumbs, and pull up on the platform to
drill a hole. The accuracy is quite adequate for drilling pads for
integrated circuits. I use a #60 high speed steel drill bit. I
haven't tried a carbide drill bit.

How much error is caused by having the platform tilt instead of move
linearly along the drill axis? Say the drill is 5 inches from the
hinge in the platform, and say the platform is raised about 1/8 inch
to drill a hole. Then the platform rotates 1/40 radian. For small
angles, 1 - cos a ~= a^2 / 2. So the error (elongation of the hole)
due to tilting is about 5 ∗ (1/40)^2 / 2 = 1/640 inch, about 2 mils.
Since I adjust the drill "by eye" so that it is perpendicular to the
platform, the error caused by misadjustment is probably similar or
greater.

Cheers,
- Jan Kok