so I've been swapping a couple of brake rotors around and seem to have ended up with a couple of the bolt heads snapping off. Maybe I did them up too tight in the first place - not sure, they've been on there a while.
Anyway - I believe I can drill them out? I've never had to do this before. Can I just use a hand held electric drill.
Any tips or pointers appreciated?
Thanks
Tim
I had that problem with a bolt in a rear hub, but since the bolt is harder material than the hub...
Ended up just snipping off the head, and just run 5 bolts plus the stub.
How about removing all other bolts, followed by rotor and then using molegrips on protruding stubs? I stripped out head on a T25 bolt but managed to get it removed by hammering in a T27 socket, so if there`s any head left at all this may be an alternative
Did the heads go when you tried to undo them? Anything left proud of the hub? Usual tricks of cutting a slot and using a screwdriver / impact driver or gripping with molgripsa re worth trying
I wouldn't try to drill it out with a hand dril - you need a pillar drill really and you need to be very careful to avoid ruining the thread. small pilot drill hole centrally and gradually increase until you can pick the remains of the bolt out of the threads
Nah, take the head off first otherwise it'll still be under tension. Use a drill bit a little bit smaller than the head of the bolt so it doesn't bind on what's left of the hex slot and drill until the head pops off. Then you can get your molegrips on the end of the bolt. Because it's no longer under tension, you'll probably get it off with your fingers.
there is nothing at all left protruding - they have broken below the top of the screw hole - so I don't think I can use mole grips or a screwdriver
Ideally you want a colbalt bit and a drill press, centre punch, lubricate and slow speed - start at 1mm and work up the bits till you get close to the threads, pick out the remains of the bolt. Worse case if you mangle the threads, take it oversize and helicoil.
I've never managed to drill out a bolt hand held and not mash the threads, you may have a better aim than me 
A hand drill will slip off the hard screw and go in to the soft aluminium.
The only positive solution is to get it drilled out on a pillar drill or milling machine and helicoiled.
Or just run it with fewer bolts.
Ahhh I see, well unless you have free access to the workshop equipment 5 bolts will be fine I'm sure.
hacksaw a slot in the top and screwdriver it out.
Take head off to relieve tension.
Boil kettle.
Pour slowly over hub and screw.
Once hot try turning out with mole grips.
If not successful. cut across screw and turn repeat but this time use screwdriver.
Get an old brake disc and find a drill bit that exactly fits the bolt hole.
Check that the bolts exactly match the brake disc holes for diameter or this wont work.
Bolt the disc to the hub with the other five bolts and using the hole in the disc as a guide, drill down 1mm. The idea is that the old bolt ends up with a nice v grove in the top of it, exactly in the centre. This acts as a starting point for the next bit.
Remove the brake disc and with a drill bit 1mm in diameter smaller, drill the bolt out. Run a correctly sized tap down and it's sorted. 
there is nothing at all left protruding they have broken below the top of the screw hole - so I don't think I can use mole grips or a screwdriver
Is that with the disc taken off?
If not, undo the rest take the disc off, even if you only have a tiny bit protruding you'll more than likely find its uber loose and can be undone with fingers or fine pointed pliers
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