Sounds like you need to make a small fixture with a hardened drill
bushing to guide things. A drill bushing for a 1/4" bit will be about
3/8" to 1/2" in diameter by 1/4" to 1" long, commonly with a flange on
one end. In your case, use a longer one to get the guidance for the far
wall. These are replaceable when worn, run about $4 from
www.mcmaster.com (page 2423)

The fixture can be made of wood (hardwood) or metal (aluminum for short
runs, steel for long runs) Make a 3/4" square hole with a snug but not
binding fit. Mount the drill bushing on the top, drill away. If you need
to make many holes you can add a set of indexing holes along the base of
your fixture. You can keep alignment by clamping a block on the far end,
sliding it along the base. Visualize a 24" long piece of 1/2" by 4"
alumimum plate with the 3/4" clamp at one end, a row of holes down the
long end.

wrote:

I've worked with wood most of my life, but I'm not as experienced with
metals... I recently found that I have to do a project for work that
involves drilling multiple holes through both sides of 3/4"x 3/4" and
1/16 thick square aluminum tube to make antennas. Imagine a TV antenna
basically... There needs to be multiple matched holes along each tube,
and into those holes, 1/4" solid round will be inserted through both
sides. In other words, the holes on both sides of the tubing have to be
aligned pretty darn well, otherwise a slight misalignment will
translate to the 1/4" round being way off center by the time it gets to
the end... Which is about 1-2 feet long. There will be a tad bit of
wiggle room since the round will be attached by threads on the end, and
a nuts on both sides of the square tube, but not a whole lot.

I had no idea this would be so difficult. I went and got a Sears 9"
bench drill press and proceeded by clamping the tube into a press vise.
I figured once I had it lined up and centered, I could just slide the
tube down for each hole... Wrong. There seems to be no rhyme or reason
to how it turns out in the end. If both holes end up being centered on
both sides, it seems to be luck more then anything. There seemed to be
a lot of slop in the spindle on the drill, so I took that back and
tried a Ryobi... Worse. The run-out on it was so bad, I could see it
with the naked eye on just a 1/8" bit. When I rotated the bit 180
degrees and made an indentation, there was almost 1/32 of an inch space
between the two. Ridiculous. I can't believe there isn't even a decent
small bench press available nowadays, but that's a different story.

I've tried using short bits, center punching first, not center
punching, 1/16" pilot holes, a countersink for a starting point...
Nothing works. I've actually had better luck just drilling with a hand
drill, but that only works for the top hole... There's no chance at
getting the alignment right with bottom hole by had. I tried one of
those portable drill press stands, but it just wasn't precise enough.
Is there some kind of a portable drill guide I could use with a bushing
or something?

I'm kind of lost at this point... Am I really trying to do something
that can't be done without a mill? That's hard to believe. The actual
physical aspects of the holes is good... Nice and clean. It's just the
alignment I seem to have a problem with. I had no idea something that
seemed so simple would give me such grief. I have a lot more respect
for you metal heads now. Any ideas are welcome.

Thanks,

Dave