Hanger replacement issue

Location
Bucks
Trying to replace my rear mech hanger last night and managed to round off one of the tiny hex bolts (that fix the hanger into the drop out), with the tool. Anybody have any ideas? For now I have replaced the other bolt and reattached the mech. Frame is a carbon Cannondale...

Ta
 
Location
Loch side.
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This is a Grabit Screw extractor. Every DIY Bike mechanic should have one, possibly two. (Rock Shox owners need a tiny little one but that's a long story).

It is a double sided tool. One side drills, the other grips and turns. Basically you put it in an electric drill ON REVERSE. Drill a bit IN REVERSE and then inset the side you can see in the picture and "drill" with that in reverse. The screw comes out like magic. No blood. No cursing. No regrets.
 
You may find that an imperial allen key or a torx key will fit inside as they are different sizes to metric allen keys. I tried removing a bent hanger on my bike and then understood why it had not been replaced, the previous owner had rounded one of the screws, but luckily a torx key fitted and I got it out easily.
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OP
Sittingduck
Location
Bucks
Thanks both. I will try the Torx, if I can dig one out from somewhere... Faling that might be a trip to the LBS before I do more damage - gah!
 
It may be a good idea to take it to someone that knows what they are doing, I am a toolmaker and I see a lot of jobs with broken taps or rounded screws where people have tried to remove them themselves and made a real mess of it and it makes the job harder for us when we have to correct everything, which also makes it more expensive!
 
OP
Sittingduck
Location
Bucks
Yep - sounds like good advice. I am still kicking myself for doing it because I knew it was a bit of a risky procedure and had dug out as much grime as possible from the screw head before engaging the hex key. God knows why the bolts for this part are so delicate as it seems obvious that it's likely to be grimy and potentially difficult to remove.
 
Location
Loch side.
Yep - sounds like good advice. I am still kicking myself for doing it because I knew it was a bit of a risky procedure and had dug out as much grime as possible from the screw head before engaging the hex key. God knows why the bolts for this part are so delicate as it seems obvious that it's likely to be grimy and potentially difficult to remove.
Don't be too hard on yourself. You'll do this only once....in every while. The biggest culprit with small hex screws is the ball-tipped allen key. These are lethal for small screws since they don't have enough engagement at that small scale to grip and they often strip the bolt. And, like you say, grime reduces the engagement as well.

Martin is right about being careful of botching this up further, but luckily on small screws you don't have the problem of breaking off Easy-Outs and other hardened steel tools in the bolt - simply because of the nature of the little beast. Anything that breaks off in there will just fall out. The Grabit tool I mentioned is perfect for the job. The reverse drill (anti-clockwise rotation) often loosens the bolt before the grip part is even engaged. It is stout and won't break. I used these in my bicycle workshop and regularly removed small bolts down to 1.5mm grub screws. I also banned ball-tipped allen keys below 5mm in size. I ground off the tips from all the mechanics' keys to prevent this sort of thing in the first place but that doesn't prevent customer accidents.

I suspect that a bike shop without one of these tools will probably hack away at the job with something barbaric and then ring up a labour charge bigger than the cost of the tool. Amazon is your friend. Keyword - Grabit. Just research the size properly, they are size-sensitive.
 
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