Originally Posted by
speedevil
Not likely that you'll be able to file them, hex keys are usually hardened. The only way would probably be to grind it, but the downside is that if you grind through the hardening, you would expose the much softer metal underneath.
Agree.
Allen keys are around 57 Rockwell. You could file it, but you'd likely dull the file a bit. Not sure that making a 4 dollar allen key is worth ruining a 15 dollar file.
And allen keys are case-hardened. That is, the hardness is on the surface (put there either by a carburizing or other agent, or by selective heat-treatment - for example using induction hardening). This leaves a tough core. BTW, hard to do on smaller hex keys - which is why I've broken a lot of 1 and 2mm and 1/16" keys. If you grind off the surface, the hardened surface (which is also stronger, btw) is gone.
Better to find the thing already made, and properly hardened.