I'm often guilty of asking questions on groups, but then not taking the time to explain how I solved the problem in the end... So I thought I'd revisit this problem:
What I did in the end is: Take the less than stellar drill press (which is virtually all of the small ones available) and improve it... On a cheap Harbor Freight bench drill press, I found the biggest problem was the slop in the spindle travel. They are usually OK for a while when new, but go out very quickly. When you lower the spindle, grab the end of the bit and see if it's lose when you move it back and forth... If it does, it's not tight enough. In most of the small drill presses, the hole in the cast head actually only has two points where the spindle tube makes contact with the casing... One at the top, and one at the bottom. The part in the middle is cast back with a little open space. In the front of the head case I drilled a hole in-between those two points where the tube makes contact in the head, and tapped it for
1/4-20. In this hole I put a nylon screw, with a tooth lock washer on the outside, and a nut behind that. I cut away the extra plastic part of the switch housing to make the screw accessible. What this gives you is an adjustable tensioner, that will put pressure on the center of the tube between the two machined holes that it slides through. Once you take the whole assembly apart, clean it all, grease it back up, then adjust the nylon screw with just the right pressure... Once it's firm, it will drill straight holes without squirting out over the surface, time after time, and you don't need to punch first. Because the screw is nylon and it's only rubbing on the tube that's greased, it rarely has to be readjusted.Then for drilling the holes... I built a fence/table out of T stock aluminum. I clamp the middle of that to the drill table, and with a scrap piece of tube, I set it so the drill is hitting right in the middle of the square tube I'll be drilling, and do a couple test holes. I then have a master template I make from styrene sheet strips. In the template I drill holes that are the exact width of a super fine sharpi pen, where I want the holes in the tube to go. I tape the template to one length of tube stock and mark through it onto the tube with the sharpi, which is where each hole will be. That first tube that's marked acts as the master for the whole batch of tubes to be done. I set that tube on the fence, match the bit to the mark, clamp down the tube, and clamp a back stop at the end of the tube on the fence. I drill that hole through both sides at once, then clamp all the other tubes in the batch down against the back stop and drill the same holes. When all of them are done, I use the master tube to set up for the next hole, and so on. I found it's important to de-burr after each hole is cut, because if the burr is sticking out, it can make the tube not sit flat, which will potentially make the hole wrong. After trying all kinds of bits, including some pretty expensive centering bits, I found that some cheap Hitachi HSS bits cut the cleanest holes in aluminum.
I've put two pieces of tube together and found that the holes match perfectly from one end to the other.
Dave