Deep in a large machine (offset printing press) an allen set screw holds a shaft in a casting. The set screw is also locked in place with a lock nut (the screw protrudes from the casting enough to fit the nut).
The allen wrench is 2.5mm and the lock nut is 10mm so the diameter of the screw is probably 6mm (1/4 inch)...
I removed the nut but the allen wrench (a new one) is slipping in the screw. How do I go about removing this? Access is only head-on (no side room for vice-grips or such). The environment is one where lubricating oil is literally raining on these parts so the "blue flame wrench" solution is out.
I tried a bit of banging on the side of the screw (yes, funged up the threads so the nut won't go back on) but this didn't budge it.
Are these allen screws hardened? Is it OK to try drilling for a screw extractor?
Thanks,