I needed some wide (2"+), slim (1/8" and 3/32) files to file narrow slots in 7075 Al. As nothing like that is commercially available, I made my own.
Tilted mini-mill's head to about 30 degrees and with 3/8 4Fl EM, cut grooves about .030 deep, spaced with .030. The grove is cut in Y and then the table was advanced the .030 in X. Repeat till it hurtZ.
Pretty tiring :), but the results are most excellent. The files _eat_ that Al like nothing else. Single cut, at an angle - I used same angle as on some "factory" files I had.
I used A2 and didn't temper @ all, for max RC. Strips were held by magnetic chuck. After HT, there's no warpage of any sort. I use "plate-quench", an invention from knife making community - after the foil-wrapped steel is removed from the1750F (for A2) inferno, it is laid flat onto a massive steel/Al plate, and then another plate is laid on top of it. It cools it 20 times faster than the air (as the steel will quench almost as good in still air, there's no benefit from it) and most importantly keeps the piece flat as it cools.
Figure some1 might need something like that one of these days and it is perfectly doable in home shop conditions.