Brake rotor allen retainer bolt head stripped
 

Good Afternoon,
Since it's above 40 degrees fahrenheit, I decided to check the back sides of the rotors on one of my BMWs. On the passenger side, the inside facets of he allen bolt are rounded enough so the bolt won't unscrew. Do I go for the drill and drill it out and then hope to grab the remainder with a vice grips once the rotor is off or do I tack weld a bolt on and anticipate I will be able to remove it with a socket. I've drilled them off before but as I recall, it was a wonderful warm Spring day and it took a bit of effort to drill it off. Anyone been there done that lately? I need to get the rotors turned as part of a brake job.

I would tack-weld

You can also drill a hole in the outer shoulder of the screw and use a punch to tap it loose counter-clockwise.

I've drilled off the head. Remove the rotor. Use a vice grip or bolt extractor to get it off. I've found that after drilling off the head and removing the rotor, most of them screw off by hand afterwards.

Or first use some heat and knock a suitable size Torx bit on the rounded allen.

your best bet is to break the rotor off the hub, chisel the remains off the hub and heat the retaining bolt up and use a vice grip to remove it.

"break the rotor off the hub"??? As in smash it off? I hope not because that is the most ridiculous suggestion. Just do as others have suggested. I just did this a couple weeks ago, drilled the head off, rotor came right off than unscrewed the bolt by hand. SMH....

Tack weld a nut to it would be my method. The head is big enough fortunately

your obviously not a mechanic or have any real world knowledge working on BMW's as this is a very common thing we do in the real world. maybe you got lucky no rust of the thread of your locator bolt. what i'm suggesting will work for everyone without drilling, welding or lost time. a new rotor is cheap to replace vs the time needed to drill the bolt out.

with a pry bar you can break the rotor off the hub with a little bit of effort behind the backing plate.
the hat of the brake rotor is the weakest part of the brake rotor so you'll get 99% of the brake rotor off and then you can remove remains with ease.

Ok - that seems like a brutal but solution of last resort. OP - drill he head off - you can use the rotor again, if you have enough meat on it. I’d rather not hit the rotor that hard, and have any collateral damage. In the end, the anchoring screw is not such a key item - the rotor gets sandwiched by the lug bolts between the wheel and the hub. If none of the other suggestions work, then get out your frustration on the rotor.

I think you have proven who is a "mechanic" and who isn't. Anyone that will take a sledge hammer to something and smash it off, putting extreme, not designed loads on bearings, emergency brake system, fasteners, suspension, has no idea what they are doing. Of course it can be done, but is it correct? Absolutely not. Not going to get in a pissing match with you and give examples of the work I have done on my numerous BMWs, Italian, Japanese cars. Just stay the f$%* away from anything I have or will potentially buy! The OP has received all good advice here on a simple problem. Just don't take this donkeys advice!