Cracking metal question

[Jordan Baker]

Hi all

While working on some Wire3 parts yesterday I removed some brazing that was holding on old chains. I used a torch to metal most of the brazing and scraped it off with a old tool. However I then noticed the metal had lots of little cracks. Was this from me heating it up or was it something to do with the brazing?

I’d like to weld up the cracks but I’ve read that any brazing left over can make the welding that much more difficult.

[Phil Waterman]

Hi Jordan

Generally when fixing cracks what I've done first was drill a little hole (1/8inch) just beyond the end of the end of the crack which helps stop the progression of the crack. Another thing I was taught by an experienced body guy, was when putting in a patch was not to use square corners if possible, instead use rounded corners. He explained that if you put a sharp corner in and weld it you will have a stress point that will want to crack.

I've had cracks like this on the fenders of CMPs and some of them had been brazed. One of them I just went ahead and brazed again, only to have it crack again, some 20 years later.

On my Pattern 12 one of the fenders had been cut and brazed, and it did not want to Mig weld. In the end I ended up cutting and grinding way the old brazing material. In one case, just took the plasma cutter and cut the crack line out leaving 1/8th inch gap. Cleaned up the plasma slag which you really need to do anyway and it welded pretty good with Mig welder.

On lighter gauge sheet metal like automotive it has been more problematic. On the Lincoln I've been restoring a lot of the body seams had been what appears to be brazed. But I'm not sure what the yellow metal really was. Those just didn't want to weld when new sheet metal needed to be added, in the end I just cut it out and replaced it with a larger patch.

Cheers Phil

[David Herbert]

Jordan,
Is it possible that it was the repeated pull of the chains that caused the cracks ? I think that I would be inclined to remove a semi circular piece and section in a piece of fresh metal. If you can find a piece of copper to back up the weld it will act as a heat sink and make life much easier.

David

[Jordan Baker]

im all good on fixing the cracks. I was just curious if they were caused by me when I removed the brazing from heating the metal to melt it?

As for the repeated pull on chain. It was just small brass chain holding some release knobs so there wasn't much weight on them.

These parts are the seat base riser used in the back of the Wire3.

[David Herbert]

Sorry Jordan that my post sounded a bit patronizing ! It wasn't intended to be.

I was visualizing a much heavier chain, like to limit the opening of a door. As it is such a light chain the cracking must have been caused by overheating the steel which then was not ductile enough to stretch back as it cooled and so had to crack. Whether it was done in the original production or by you I think is now very hard to tell.

David

[David Dunlop]

Hi Jordan.

Maybe the cracks are just the cumulative result of years of body weights moving around in the seats and road vibrations transferring up into the metal.

David

[Matthew P]

When originally brazed on somebody might have then taken a wet rag and rapidly chilled the metal so they could touch up the paint sooner? That could have caused cracks. Which might have gone unnoticed or ignored if there was a cause for a expediency and an attitude that they would still hold.

Just an idea?
Matt

[motto]

I watched a friend chase a crack around a car fuel tank one day whilst trying to do a brazing repair. The crack appeared to be caused by the brazing process and the job ended up very messy.
I saw it but I can't explain it.

David