On Mon, 20 Feb 2006 21:11:40 GMT, John Doe
wrote:

I need to drill some fairly accurate holes at an angle through some
aluminum square tubing (or whatever you call tubing that's square
instead of round).

I guess the main problem is that my cheap drill press has some play
in it so that the bit doesn't necessarily follow the intended path
straight down. So when I put the metal at an angle, the bit is going
to move towards the deeper side as it drills into the metal.

... should I use something to press on the spinning chuck shaft so
that it drills closer to correct?

... if I were to drill straight down through the aluminum with a
smaller diameter bit, when the aluminum is angled will the larger
drill bit end up going through the center of that hole? (Yes, this
is easy enough to test)

... is there some trick I don't know about?

Thank you.






Since you need accurate hole location, and all you have is a drill
press, then you need to make a drill fixture. Depending on the number
of holes you could make it out of aluminum. If you need to do lots of
holes then aluminum could still be used but you would need to buy a
couple drill bushings. They are pretty cheap, and harder, lots harder,
than your drill. I don't know what tools you have or how handy you are
but here's a couple suggestions. Make a box, by bolting 1/2" plate
together, that slips over the tube with little clearance. Drill and
tap a hole for a screw to hold your part in the fixture box, so that
it can't shift while drilling. Set this box up at the angle you want.
Grind a flat where the drill will enter, drill first with a center
drill, then an undersize drill, then ream or drill with the final size
drill. Turn over the fixture and repeat. Then you can drill through
from the outside for each hole. This all requires careful layout. If
you need the drill bushings then order them and the reamer for them at
the same time. To support your fixture you could make an angled
support out of MDF. This would cradle the fixture at the correct
angle, is very repeatable, and would allow turning over the fixture
fast. You can put a dowell into the MDF to locate the fixture the same
each time. If you have only a couple parts to do then the whole thing
could be made of wood. If only 1 part then clamp some MDF to the part,
grind a flat so the drill starts easily, drill undersize, then the
final size. The MDF is dense enough and hard enough to act as a drill
bushing for a hole or two into aluminum. Good luck!
ERS