Okay, so basically i have a brake caliper (its off a bike) which the bolt has snapped off.. any advice for getting it out?

The bolt is steal
The caliper is aluminium
So there is a bad case of corrusion between the metals.

I've tried WD (soaked), cutting a flat head groove, even drilling (the drill pieces blunt quick).

Any advice?

Thanks
Ryan

 

Lots of heat and use tool steel drill bits or cobalt, the danger is slipping off the harder steel but so long as it has a decent pilot hole and you go slow will be no problem, had to do this on cozmeisters head bolt as someone had chewed the bolt head up, went up 0.5mm at a time took about 45 mins but did the trick.
A pillar drill really helps a lot if you have one.
You will always get corrosion between steel and alloy, this is called differential metal corrosion, quite normal just soak in grease coppaslip or similar, try to exclude all the air being able to get to the bolt threads etc to stop in future.
tabetha

 

If you have a welder then use it to weld a nut onto what is left of the bolt shaft. This method will more or less guarantee to save you the bother you'll inevitably get trying to drill out the bolt.

Failing that, as mentioned - you'll have to drill it out.

The reason why your drill bits are becoming blunt very quickly is because you are probably using an incorrect surface speed for the diameter of the drill bit and rotating them at the incorrect speed; larger diameter drill bits need to be rotated far slower than smaller ones. High RPMs with larger diamter drill bits causes excessive heat, its the heat which dulls the bit quickly.

If I were you I'd consider not only using the correct RPM but also using oil to both cool and lubricate the cutting edge of the drill bit.

 

drill into it with a good drill bit colbolt one needed realy then lighty heat the caliper very lightly if ally as u say then bang a torx bit into the hole u have driled and try to crack it off when it cracks go back and forth with it and very slowly wind it out. If it looks like it not going to come out rather than fuck the caliper up have it spark eroded