moto367

I have a 1996 Mongoose mt. bike frame made w/ Tange 4130. I would like to add disc brake tabs for the rear. My question is: should I "draw" or temper the area back after I weld the tabs on? I planned on tig welding them on but I'm beginning to think maybe brazing is the way to go. Thanks for you thoughts and opinions.

NoReg

No you don't need to do that. You never quench a weld or brazed area, which is to say imerse it in water, or blow compressed air on it to rush cooling. It won't harden after the welding is done, and in any case 30 points of carbon is not that much, normally 40-50 points are pretty much the lowest, without using super quench, that will harden. So just let the steel cool at room temp, and you are good to go. you can however damage the steel simply by burning it with too much heat. The problem isn't something related to heat treating but, I guess, oxydation.

TIG or braze is up to you . TIG leaves less of a heat affected zone. It's like walking on fire, it's not only how hot, but how long you stay in one place. TIG leaves the least heat affected zone because it is hoter and it is faster, both are good. But overall you should probably consider your tools, your skills and anything else that might make you favour one method over the other, rather than heat issues since done properly either is fine.

I don't know that frame, but often a retrofit will put too much stress on a bike not designed for disc brakes, the brake loading is completely different.

moto367

Don't mis-understand me. I don't want to quench w/ anything other that the ambiant air. What I am wonder is should I stress relieve the area w/ a torch after I weld? Not an extreme amount of heat, just enough to relieve it. But you say it won't harden in the weld area? thanks for your input.

NoReg

I didn't really think you were. Though I have seen these threads before and that isn't an unusual perception. You are safe, there isn't any need to reheat. Things a person may need to be careful about include. Not letting the heat get to the drops, if they are silver soldered in shouldn't be a problem here really. Another thing is checking on the alignment of parts. Any time you attach one piece of metal to another there is the possibility of distortion occureing and the alingment going out. Adding brackets is not an unusual operation though.