OT .... Welding Mild to Cromoly steel
Turbo Mini Forums

I know there are only a few on here maybe capable of answering this question with any sort of reasonable validity, but here goes anyway :)

I'm looking for advice on welding a mild steel bracket onto a cromoly tube. Basically I want to add a caliper mount onto a bicycle frame that doesn't already have one. Now I know it should really be tig welded, but then there is the complication from what I have read of pre weld heating and post weld cooling and temper, but the mig and gas is all I have, so, the plan is to position the mild steel brackets with the caliper fitted, tack the brackets onto the cromoly with the mig and then braze it from there on in. All the mig welds will be for is for initial positioning of the brackets so I can avoid excess heat into the caliper during positioning, then use the gas to finish with the brazing, thus avoiding all the technicalities of cromo tube and temper.

Any advice? Is what I propose with the mig doable? and which wire would be better, the stainless or the mild?

thanks in advance

I had the exact same problem years ago and a family friend made and stick welded some mounts on with no problem.

chromoly can be welded with mild steel wire just fine. And people welding cages from chromoly cant really do anything about pre or post heat.
TIG would impart far more heat than MIG would anyway, with being a much slower process.

Or ask the question on the MIG welding forum

Edited by stevieturbo on 9th Feb, 2013.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

cromo is still steel so mig welding is not a problem.

I migged some mild steel floor pans into a Geoff Hauser cromo frame many years ago, just treat it as steel

I seriously doubt it!

Great! :) thanks guys. I can crack on with it :)

the thing to watch with welding/heating chromoly is like with any high carbon steel, if you over heat for too long you you can burn the chromium out of it, and once it burns it becomes dirty and makes it very difficult to work with.

just try and heat the area up evenly and don't hold the flame too close. mig should be fine as it diesn't put as much heat in.

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

following on, I finally got round to actualy doing this. I made the bracket from 4mm mild and shaped it to fit nicely along the dropout and stay tube then tacked it on with the mig on each corner. I added two more tacks on the inner side and then doube checked the alignment, and adjusted the pitch a little as the tack welds had obviously shunk a little as they cooled (my main concern with welding it). Once I was happy with the alignment, I brazed the bracket onto the the frame along the entire length of the join and built up the shoulder on both sides for added strength. Cleaned everything up with the wire wheel and a quick tidy up with the grinder and I am well pleased with the result. It took me a couple of hours start to finish with all the assembly/ disassemby, fabricating and double checking. Last job was to cut off the V brake posts and grind them fluch with the frame. Spot priming with high build and a flat over for the top coat of paint is the next task.

Good job, what bike is it? I'm guessing some sort of trials bike going by the chain and seat stays?
And if so, how come your changing to disks rather than hydraulic rim brakes

2000 Marin FRS :)

Edited by Sprocket on 19th May, 2013.