Broken Set Screw on Knob - Help Needed

[Robbie Collins]

The blade-type set screw holding the remaining knob onto the '57 Guild Aristocrat in the background is missing one leg. How might I loosen this screw without damaging the knob? I'm thinking about grinding down a small screwdriver into a half-round shape.

[Ned Knepp]

That  sounds like a good idea but have you considered just making an "insert' to slip into the hole with the screwdriver.  Once the screw is broken loose, you may not even need that. I think I would run a properly sized tap through after removing the screw to insure the threads are OK. 

[Steve Bettesworth]

You might be lucky with the screwdriver, I think it may depend on how clean the break is. I'd drill and use an easy out thread extractor. 

Steve

[Frank Ford]

Some of us use left-handed drills for this kind of job.  Often as you try to drill out the screw, the drill will snag, speeding out the broken screw.

[Len Biglin]

I'd probly warm up the knob with a desk lamp and see if it will come off , then worry about the screw.

[Robbie Collins]

Thanks, everyone, for your suggestions.

For the sake of knowledge, I tried it two ways. I made the half-round screwdriver and it worked great. Then I put the broken setscrew back in using needle nose pliers and the bespoke screwdriver, found some similar screws, broke the leg off of one, cleaned it up with a file, super-glued it to a small screwdriver, and out came the screw.