I reckon a thermal lance would have made less mess.

Couldn’t you get a hacksaw blade down the slot of the crank and cut through the bolt?

Dremel ? Masonry drill bit ? are they stone cranks?

Would it not be possible to drill the bolts from the back?

Christ!…that’s only fit for ebay now 😀

Cheap screw/stud extractors are cheap for a reason, i have a snap-on set that have proved invaluable but even then i only use them as an absolute last resort with my fingers crossed.

What is a thread of this nature without referencing rocks, superstars etc?

Good job. Do you have anger management issues?

Those won’t do much good on steel !

Dremel, drill them from the “wrong” side, or use a left-handed drill bit.

And a few litres of hindsight 😉

Drilling from the back was my though. Not because you’d drill through it all, but because you’re applying heat where it has actually seized and because the direction of rotation is trying to undo the bolt rather than driving it in.

Recently had a colleague in a similar predicament as gofasterstripes (but not quite as spectacular).

He’d rounded off one head with his cheap allen keys, I managed to nip the other pinch bolt up which took the pressure off the rounded head and allowed me to undo it with a proper allen key.

Might give the gofasterstripes method a go next time though, looks a lot more entertaining 😀

Buy better drill bits!
Cheap HSS drills are a false economy, as they usually don’t drill anything harder than aluminium, unless you get a lot of pressure on them. Also, I’m pretty sure Shimano use stainless bolts, which will work harden the moment the drill stops cutting and starts rubbing.
Stainless is a rubbish conductor of heat, so you have ensure you are always cutting, as the moment the cutting tool rubs, it’ll heat up resulting in work hardening. Applying a bit oil helps to transfer heat away from the cutting edge, but nothing will compensate for a rubbish drill bit.

Getting seized bolts out is something that is made far easier by lots of experience.
For pinch bolts on cranks, once the other option of hammering something bigger in has failed, take a good quality sharp 6-7mm drill with plenty pressure and a slowish speed and drill the head off. Once the head is drilled of, you should be able to get the cranks of the bike, then continue drilling with a smaller drill bit somewhere more suitable i.e. a vice or pillar drill, to get the rest of the bolt out if needed. The ideal situation now the pressure will be of the bolt, is the drill will snag the remains, and screw it out.

This is what good local bike shops are for! (Of course I’ve never got a pair of cranks similarly stuck myself…)