[ATM] Cutting thread in aluminium

[Göran Hosinsky <hosinsky@ya.com>]

Is there any special trick to cutting threads in aluminium?
I was cutting a M5 thread by hand in a 15 mm thick piece of
aluminium, unknown type, when the tap (tap no 1 in a three
tap set) sized up and broke. I was pouring alcohol over the
cutting.

At my second try, with a new tap, I managed to back out again
when it began to stick. I then drilled up the hole to a bigger
diameter and found to my surprise, that the drill had difficulties
to go through the threaded part of the hole, it was like the
aluminium had been hardened at that point.

Any advice would be welcome as I have quite a few holes that
I want to put thread in.

Goran, La Palma
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