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I have some "very finely-threaded" screws with flat endings and some un-threaded aluminum "bar" (2mm thick). I wish to have that "bar" threaded according to the screws, but since they are not self-tapping, I can't directly (I tried, and just managed to eat away the aluminum).

I have a couple of questions:

  • Can I thread (tap?) aluminum using a self-tapping screw, just like you would with wood?
  • If so, can I do it with threads of differing "fineness" (number of revolutions per mm along the shaft)? I find it very unlikely I'll be able to find the right ones.

Please excuse me if I have used any wrong terminology, English is not my primary language. Corrections are very welcome!

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Typically you would need to drill a pilot hole and then thread with a thread cutting tool such as this: enter image description here

however, since you are only using 2mm aluminium it should be soft enough for you to cut your own thread. Note: this will never be as clean as using the proper threading tool:

your problem is that you used a self tapping screw, I would recommend that you drill a pilot hole slightly smaller than your intended hole, then use a machine screw to create the thread (basically by tightening the screw into the pilot hole)

A bonus, is that you can also look out for Thread cutting machine screws. In this case your pilot hole must be just big enough to fit the tip of the point (as you can see it tapers at the end)

enter image description here

  • Question states "flat ended screw" - a self-tapping screw would probably work fine. If the questioner has a grinder or files, the "self-tapping machine screws" illustrated in this answer are not too hard to make from "flat ended screws" with a little grinding. Be sure to taper-grind away the threads and put in the length-wise slots that actually cut the threads. Given the materials, that should be fine .vs. trying to track down a matching tap. – Ecnerwal May 3 '15 at 21:21
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You should use a thread tapping die to meet the threading of your screws. Pre drill to the appropriate size, apply threading oil to the die, then slowly tap the hole. This isn't very complex, just requires a special tool.

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