On Tue, 1 Jan 2008 15:18:47 -0800 (PST), wrote:

I've got blisters on my hands from taping 20 holes manually and I have
hundreds left to go!
What machine or tools do I need to tap 5/16th-18 holes in aluminum? I
am using T slotted 1.5" square tubular aluminum for a lot of projects,
ranging from a workshed to a photobooth to a workbench and having to
manually tap the ends of this metal is going to kill me! I'm
specifically using http://www.8020.net/T-Slot-1.asp this stuff. I
bought two specialty taps that are a combination drill/tap bit from
www.mcmaster.com part # 2748A43 At $20 each they are pricy and I've
already busted them both after only about 6 holes each with a hand
drill.

Any help please?

First off, I don't understand why you need the combo drill-taps.
Aren't the holes already in the extrusion, ready to be tapped as
required?

I've done a lots of tapping on Item extrusion (though fortunately
never as many as 500 holes at one time) and have found spiral flute
taps to work best by far. See McM p/n 2529A19. Use an aluminum
tapping fluid (e.g., Alumtap), or wax stick lube (McM 1311K1) applied
to the tap.

I do the short lengths held in a fixture with a quick acting clamp
that mounts vertically to the front of a Bridgeport table. Anything
longer than about 3-1/2 feet long would require a hole in the
floor.g As has been mentioned, a drill press and tapping head would
also work, but you'd still run into the length limitation.

A *good* 1/2" reversing drill handles the long lengths. It's touchier
and less convenient than tapping on a mill or drill press, but not bad
once you get the hang of it, especially with the proper taps and lube.

Let me know if you'd like a photo of the locating fixture.

--
Ned Simmons