Pure aluminium is a gummy material, is it possible to drill a clearance hole to avoid tapping the full thickness of the material?
Mike

It's just a heatsink – just drill clearance size through and use a bolt, lockwasher, and nut.

I would try water & dishwashing soap mix.

In a mass part production environment most soft metals are thread formed not cut. The main problem is getting a reasonably accurately sized hole as with small thread pitches there is little to deform. I would drill a smaller hole first then open it out to the required size, I do this for my small cutting taps to get a better sized hole and therefore better fit thread.

If you get a tough one which needs threaded then I make the hole a bit bigger, ream it out a bit

Means less thread engagement but tapping is far easier and it always seems to hold fine

Adapt the system for the job kinda thing

Slightly OT because not a hobby solution, one of the neatest solutios I've seen in heatsink fastenings is tha ADVEL RivScrew.
These look like a pop rivet with threads on the shank the mandel is hexagonal and as as it is drawn through forms the central hole into a hex and expands the threads into the heatsink. This gives fast industrial fixing but you ann unscrew the installed fastner with an allen key and refit it. They are also use on some platics and composites as structural fastners.

https://rhf.co.uk/product/avdel-stanley/speed-fasteners/rivscrew/ (random supplier)

Thread forming screws are also an option. Taptite is a major brand. While I've used a lot at M3.5 they are available in smaller sizes. Down to a surprising, to me at least, M1 x0.25

https://taptite.com/images/REMINC-Catalog-English-web-quality-20210119.pdf

Robert G8RPI.

QUOTE Spiral Point NO this will fill your hole with swarf or better spiral flute – Yes much better

+1 for Roberts suggestion of Taptite screws.

These are tri-lobular in shape, essentially the same as thread forming taps. I could be convinced that they actually work better than proper thread forming tap in gummy alloy. Use as is or, if something really secure is wanted without undue tightness, run a normal screw into the hole.

Last time I bought some a small box was usefully cheaper than a thread forming tap or a set of decent quality normal taps. Given the likelihood of breaking taps in gummy alloy I figured that finding storage space for the 40(?) odd screws I wasn't going to use for that job was a fair trade off. Over the years they have slowly gotten used, mostly on an "as I have them" basis.

Clive

Try using Methylated Spirit as a lubricant, you need to add frequently with a brush, we used to get L34 aluminium, an aircraft grade material, very soft and gummy, horrible stuff to machine but meths worked well as a lube.

What Elf 'n' safety would say now ????

John

It;s not the drinking of it that is a problem. It's the blindness and the brain damage that can follow. Ironically, the cure is to drink proper ethanol. It converts the formaldehyde that forms in the metho drinker's stomach into a less harmful chemical, or something. So the emergency room doctor told me on night shift at the hospital where I worked. In the absence of the hospital pharmacist to dispense pure ethanol at 4am, the good doctor had to give the miscreant a big slug of his own best scotch from his office. So we all sat around and had one, just to make sure old mate was OK.

Robert and Clive, we used to use tri-lobe thread forming screws in 6mm thick mild steel. I think we got ours from Lancaster Fastenings. They were used for securing cable trays and saved time and broken taps as they were often being used in hard to access positions. It became an economically viable process when battery powered drills and nut drivers became cheap and reliable.

Martin C