The Stovebolt Site Forums The Shop Area Paint and Body Shop Welding over brazing

I've got a couple of cracks in sheet metal that were previously brazed but now cracking again. I would like to weld them. I have read online that you have to first remove the brazing. My question is just how thorough does the removal need to be? I don't want to thin the metal any more than necessary trying to get every bit gone. Comments appreciated.

Dennis

Brazing actually incorporates the filler metal into the steel for some distance, so you probably need to cut out maybe 1/16" either side of the crack to be sure you get the brazing filler out. Welding will vaporize the remaining brass filler metal, but will also contaminate the weld. The location of your cracks will dictate how thorough you need to be. Can you post pictures of what you need to repair?

Yep, I'll take/post a picture tomorrow.

Dennis

I’ve done similar where I used small drum sanders, flat sanders, whatever fit the contour, and sanded just until I saw sparks. As you can imagine, it takes some light pressure and quick reflexes to keep the sheet metal as thick as possible.

If the steel was pitted from rust prior to brazing it will be pretty intense work trying to remove the filler. You need to get it all or welding will give you fits.

Here's a couple of pics. I'm using my Dremel to clean up as much as I can. I will work at it some more, but what do you think about the success of welds would be as is? I have a MIG welder and also have a TIG on its way so could go that way too - once I learn how to use it, that is. Full disclosure - if you don't recognize the part, it is the front cowl of a Morgan. Not Stovebolt, but I would think useful to some anyway.

Dennis

I would almost recommend cutting that slot completely out on the left pic and replacing it with a small patch and recutting the slot. But it's hard to tell from a picture. It's a high stress point with the slot there and even a weld will have trouble staying intact. Moving the weaker point away from the slot would help keep them from re-cracking. Or maybe put a doubler behind the cracked spot if the assembly will allow that.The one on the right can probably be successfully rewelded, assuming you get the braze metal completely gone.

Shush!, that's a custom Stovebolt part, correct?

Depending on what is behind that piece, you could clean the back side well, place a small piece of metal (anything but aluminum or magnesium...copper, brass, steel) over the visible crack and simply use silver bearing solder (Stay-Brite is the best by a long shot). Here are the upsides: cost--tremendously less than any welding you can do, heat--much less than welding or brazing (think around 430~440 degrees), strength--greater than brazing (a lap joint is over 10,000 psi). Joins dissimilar metals very well and get this: you can do it all day long with a handheld propane torch. Final benefit? When you're done, dress the joint just as if you had used lead. It sands well enough you may not even need filler and it absolutely won't rust. I've even used this stuff to fill in pitted rust spots. Once you get the hang of it, you may think you've just been given a magic wand. Neutralize the flux with some soda mixed in water.

OK, went to work with the Dremel with various carbide bits, disc, etc. I felt like a dentist removing gold fillings! Anyway, take a look and tell me what you think. I included one of the underside too. Would a weld bead on the underside toward the edge be benificial. I'm thinking that would word as well as welding a doubler as suggested. Jon, the silver bearing solder sounds interesting. Not sure I want to do that here but have another spot that I think it would be perfect.

Dennis

It's pretty simple. You take out the braze completely Then you either fill the hole or slot with weld or you weld in a small patch. It's just repair 101 as if it was rust. Silver solder is for making crafts.

If you have a tig welder coming you could also tig braze that. Tig brazing uses a silicon bronze rod and it lays down similar to a tig weld but does not melt the base metal.

TIG brazing would be basically the same as brazing with a torch, just a different heat source. I think a weld repair would be preferable.

Yes, you could run a weld bead on the back side, but I don't believe you need to.

I think it is instructive to remember a few things:
Silver bearing solder will bond dissimilar metals amazingly well, so rust and paint are the only things you need to remove in this case.
It applies at such a low temperature it won't deform nor warp thin metal and you can apply it with a handheld propane or MAPP torch.
It is easy as pie to use...once you get the hang of it, you'll be amazed.
If you make a mistake just heat it up, shake or brush the solder off and do it again. Heck, at that temperature I've even used a work glove to brush molten solder off.
It is stronger than a 99 cent Mexican plate lunch.

In the 60s, I took advanced level welding classes for 9 months and then worked as a specialty commercial welder until I realized how fast that work could turn a young man into an old man during the summer in Texas. The instructor had worked all over the world and had a very impressive knowledge about the subject not to overlook a doctorate in industrial arts. He was very big on using the right stuff for the job at hand...ie, not using a Howitzer to kill a rat. We spent weeks learning about solder...the myriad different types, all their properties, how to apply them correctly and all the benefits and advantages from using them. I've mentioned silver bearing solder on this forum numerous times, and usually I get the idea about 5 or 6 people around here have even heard of the stuff. My sincere suggestion (to everyone) would be to study and get familiar with it. With silver bearing solder you can join/repair mild steel, copper, brass, stainless and cast iron. A couple of years ago I even used it to repair a cracked carburetor float bowl with success. IMPORTANT NOTE: silver bearing solder is NOT the same as silver solder. Silver bearing solder is a non-lead solder with properties you won't find in any other non-lead bearing solder. Good luck.

Tig brazing is much cleaner and neater than using a torch, no flux, more heat control, and more control of fusion. Tig brazing is much more than just a different heat source.