If I understand your project you want to use the extruded holes in the ends
of the material to fasten them together with 5/16 18 screws.

If the hole is an appropriate size or you can enlarge it to the correct size
you can buy thread cutting screws that you can skip the tapping process
altogether.

Mc Master sells these in 5/16 18. Mow all you need is a socket on the end
of a hand drill with a clutch and you are in business.

--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
they come up with this striped stuff.
wrote in message
...
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?