I was re-reading my copy of Welder's Handbook because my practice welds on some scrap were weak as hell when trying to weld 18ga to some 12ga (rosette welds) to beef-up my seatbelt attach points that rusted out. Needed a break to do some research and find out what I was doing wrong.

The author, Richard Finch, is big on brazing automotive sheetmetal repairs as opposed to fussion welding (MIG, Arc, etc.), particularly when it involves pre '80 cars that weren't assembled using HSS (High Strength Steel). He says that the high temps involved in fussion welding actually weakens the surrounding metal, where as the lower temps involved in brazing doesn't. You can't braze butt joints like you'd use to attach outer body panels, but the reinforcement kits like Mark's (Engman) inner long stiffener's and Brad's 10ga beasts would actually be much stronger (at the attach points). His example is taking 1" x 5" long strips of .060" mild steel, overlapping the ends by 1" and brazing them together. In a pull-test machine it takes over 3000 lbs. to pull them apart and it's always the base metal that breaks, never the brazed joint. Since lap joints are the preferred joint when brazing, and all of the weld points (holes) on the reinforcements are essentially lap joints, wouldn't it make sense to braze in the stiffeners rather than MIG weld?

Or then there's always the possibility that everyone does braze their stiffeners in, and I'm just assuming they've been MIG'd


Kevin

IIRC the front post where the dorr hinges bolt to is brazed to the longs.

as for brazing in a stiffing kit you could to to but there are 2 major problems with it :
one you need a perfectly stripped surface to braze to, sand blasting would do it

two all that heat would warp the hell out of you car, because you would need to heat some much of the car to 500 degrees if you use brass ( the normal braze mat. )

but i would bet a silver bearing solder in the temp range of 350 would be almost as strong as the spot welds because you would be making a laminate which is always stronger, but it would still warp

scott thacher

"The author, Richard Finch, is big on brazing automotive sheetmetal repairs as opposed to fussion welding (MIG, Arc, etc.),"

Hi Kevin,

He may be big on it, but he is almost alone in his thinking. You won't find serious metal shapers or restoration people using that method. The best reason for brazing is to join disimilar metals. The author probably had a hard time welding the small stuff, and came to a convenient conclusion. Brazing is kind of like glue, it has its uses, but seat belt anchor points, roll bars, body repairs, are not among them. You might get a way with it, but welding is superior in every way. If you share some picture of your welds maybe we can help you figure out what is going on?

John www.ghiaspecialties.com

interestingly, Carroll Smith is big on "nickel-bronze welding" (fillet brazing) and says it's the method by which most British sports and formula car suspensions are fabricated in 'Prepare to Win' (a publication that predates the wholescale use of composites such as carbon fiber in primary structure...)

it requires a flux and scrupulous cleanliness and doesn't seem like it's appropriate for occasional use. but if you're already set up with an oxy/acetylene gas outfit it could be worth checking out.

i don't think i'd trust seat belt mounts to anything i could find at the Ace Hardware, tho ...

Bronze welding, which is often called brazing in the US, was a very common practice in attaching mild steel tubes together to make spaceframes in the UK at least from the 50s through the 80s. Considerably less heat is involved, and thus considerably less distortion in the joint resulted. The fillet left behind also does a nice job in spreading stresses in the joint. The chief difficulty with this technique is that craftsmanship is critical. The tubes must fit together very well with very small allowance for gaps.

MIG and TIG have pretty much taken over from bronze welding these days, as both allow more slop in the fit of the joints, both are somewhat easier to do than torch welding, both are considerably faster than torch welding, but most importantly, the cost of the machines has fallen to the point that they're easily within reach of even the poorest fab shops. TIG machines, especially, used to be very expensive, and reserved only for aerospace outfits with their nearly unlimited budgets (and far higher standards).

If you have a torch and know how to use it, buying a set of bronze rods is cheap and you can practice awhile to see if you can produce good results. However, actual MIG (not just wire-feed with no gas) will produce good welds quickly and easily, esp. for something like rosette welds for attaching things like long reinforcements. If you're getting weak welds with MIG, you need to improve fit, and make sure everything is clean, clean, clean. Also, if you're having trouble with MIG, brazing is harder to do properly, so don't look there for a shortcut.

Brazing in theory would be great for a stiffening kit.. welding only attaches it at the holes and around the edges, brazing would wick out from the holes, and bond it everywhere. That said, I don't think it would be practical.. for small things, getting that tight fit that allows capillary action isn't too hard.. for an entire stiffening panel it would be nearly impossible. It would also be very hard to tell if it wicked out from the holes, or just dripped down and landed someplace useless.

While removing paint and filler layers from my car I have found 2 or 3 spots where a PO had panel repairs brazed in. These were probably rust repairs the largest piece is a 6x6 inch square. I have found these brazed pieces in good shape under the bondo and very difficult to remove so I would say that the process works quite well for thin panel repair. Just my $0.0157.

One thing worth noting... it is VERY difficult to weld something that's been brazed... so don't plan on brazing it "for now" and then going back to weld it later. (you'll have to get all the brass off.. not easy)

I've done quite a bit of "silver soldering", but that was all line-sets for air conditioners, so I was hoping that brazing would be more up my alley (plus my father-in-law has a big-ass oxyacetylene torch set sitting there collecting dust). I practiced all day Saturday with different settings to see what gave the best results for the thickness of the metals I'm going to use to do the repairs (18ga and 12ga mild steel). I had very good results (eventually) with all of the different joints "except" when trying to rosette weld the 18ga to the 12ga. The welds looked pretty, but when I gave them the BFH test the 18ga popped right off without too much effort. I ground down all surfaces to shiny metal, and clamped the pieces together for a good fit, drilled 3/16" holes in the 18ga, and concentrated the weld on the center of the hole to get the best penetration on the 12ga plate. When I cleaned off the slag, the welds looked real nice, but after the BFH test it didn't look like I was getting hardly any penetration into the thicker metal (Note: I'm using a Century 80 flux-core welder, could be part of the problem), in fact it appeared that there was a layer of slag at the surface of the 12ga plate at the point of the weld everytime . I try the next higher (hotter) setting which worked great for welding 12ga to 12ga, but it was too much for the 18 ga. I wish I could throw up some pictures to show you what I'm talking about, but my camera absolutely sucks at close-ups

You guys make a good point about getting a "good fit" for brazing the repair panels, could be tricky getting them to fit just right, but would I have the same problem with mal-fitting MIG welds?

One possible solution would be to use "clecko buttons" to hold the panel tight to the structure during the weld/braze procedure. I'm actually considering taking the pieces to work and riveting the pieces I'm having problems with using monel solid steel rivets (then I'd be good for 10 G's in the corners ).

Maybe I need to find someone around here that has a Gas MIG (I know, redundant) and see if the flux-core wire is causing the problem.

Just had a thought.... Would it help if stacked the pieces when drilling the rosette weld holes, allowing the drill to slightly penetrate the 12ga metal (divot)? Then the weld would start sub-flush to the thicker metal. Or maybe I need larger holes in the 18ga (1/4", 5/16") to expose more of the 12ga.........just grasping at straws at this point.

There is no comparison between proper mig welding setup and prep compared to brazing. Brazing, to be done properly, requires super tight tolerances, were talking can't see the light through the gap tight. It's not really practical for something large or difficult to get to. I'd be happy to trust my life to either a brazed or mig welded connection, but it would take ten times as much prep on the brazed joint. It also takes considerably more skill to make a proper bazed joint compared to mig. Take John up on his offer to help you out. Good Luck.

Brazing does not bond like conventional tig or mig welding does.
Brazing lays on the surface like a glue and the only strength is from the surface irregularities. That is why the peices have to fit very well together so that the gaps can be filled with braze to maintain strength.
Welding on the other hand melts the parent metals and fuses them together as one piece of metal. The metallurgy can be negatively affected from the heat but if that is a concern it should be pre-heated and controlled on the cool down.
I personally would not use brazing on critical strength members like suspension pieces or seat belt supports.
Partly because of what I know about it's limitations, and partly because the British automotive engineers did it

Well it appears that the general consensus is brazing the repair panels is a bad idea. So, any suggestions/tips on how to get better penetration on the heavier gauge metal (aside from "have someone else do it", or "buy a better welder" ). I'm all ears!

Turn up the heat

Tried that, too hot for the thinner metal....maybe I should try pulsing the trigger on the high setting and see if I get a better bond. Can't hurt, I need all the practice I can get!

Up the heat some (higher amps) and place a big block of brass or copper behind the sheet metal, , clamp it tight. This will serve as a heat sink, to help prevent burn thru of the base sheet metal.

Also it is easiest to weld simular thickness of metal together, so if you can change one of the parts to the smae thickness as the other, that will help.

Best advice is practice, practice, practice on scrap metal. besure it is the same kind and thickness as you will be working on, as there are different responses to welding. Do not be afraid to experiment with different settings. Be sure your wire is correct alloy, and for best results use a gas shielded MIG rather than a flux core MIG, much better results,a dn much easier to use.

i agree that brazing is not best choice for high strength applications in your car, nor bady repairs (I am trying to undo decades old braze repairs on a 356 body, yuk!!!!)

good luck dave

A guy I work with suggested upping the hole size in the 18ga from 3/16" to 1/2" in an attempt to liquify the heavier gauge metal first. I'll try all of the posted pointers and with any luck I won't have to use the emoticon again.

Thanks for all of the input guys! Always appreciated!!

The type of rosette welds you are trying to accomplish are very difficult with MIG, ie. 18 ga on top of 12 ga.
Your idea of drilling part way into the 12 ga is likely to help, since the base metal will melt more easily without overheating the 18 ga, and the edge of the drilled metal will melt more readily as well.
Also a larger hole (1/4, 5/16) is a good idea since the smaller hole fills up before enough heat is developed to melt the thicker base.
You would have a lot of trouble brazing such joints since you can only apply heat to the outer (thinner) panel which would heat up and grow away from the underlying panel, causing much too large a gap for the bronze filler to wick into.

Yep Chris, I've pretty much scrapped the brazing plans (for now ). Gonna try the "drilling part way through the thick stuff" and "bigger hole in the thin stuff", or even a combination of both. The 12ga plates are only at the seatbelt attach points, but they've got to be solid for obvious reasons. Glad I did some experiments (BFH test) instead of assuming they were good just because the outside of the weld looked purty.

I also borrowed an old welding helmet from a buddy (flip down type), it works WAY better than my fancy auto-darkening helmet. The auto-dark won't get dark enough to see what the hell you're doing.......useless POS.

You might be surprised how many factory spot welds fail that test.

Big Fucking Hammer? I love that test!

In all honesty, the input provided above about brazing is true. When in my industrial metal class in highschool, the welding chain went as such:

Oxyacetlyne -> Brazing -> Stick (Electric) -> MIG -> TIG (stainless) -> TIG (aluminum)

Aluminum was the hardest... stuff melts so damn fast when it's hot...

A properly done MIG or TIG weld will outlast brazing welds. If MIG or TIG welded aircraft parts can withstand the test, undoubtedly they will last on your car if done to the same standard.

For the problems you are having (2 different sized metals)... To melt the thicker metal you will need a higher amperage. As you noticed this burns the thinner metal away quicker. Adjust by increasing your feed speed and moving faster. It is doubtful with different sized metals you will have perfect welds... Although if the thinner metal is fused completely to the thicker metal your job is done. Not much else after that.

Also, avoid using fluxed rod. The slag is from the flux shielding on the rod. When the metal cools it 'bubbles' to the surface with any impurities. If there are no impurities, well, the slag will become deposits in your welds. Using Argon will eliminate this problem.

That's pretty much all i can say... besides practice practice practice... that will be your best friend, as many above have mentioned

One of the problems with flux core is the lack of being able to see what the weld puddle is doing.

For welding thin material to thick material, you must use a hot setting, concentrate the weld on the thick stuff, and whip over to the thin stuff, and quickly back to the thick. Use the trigger to control the heat if the thin material starts to go away.

John www.ghiaspecialties.com

SUCCESS!!

I did 4 of each weld in some scrap:

1/4" hole in 18ga, 12ga no drill divot
1/4" hole in 18ga, 12ga with drill divot
5/16" hole in 18ga, 12ga no drill divot
5/16" hole in 18ga, 12ga with drill divot
3/8" hole in 18ga, 12ga no drill divot
3/8" hole in 18ga, 12ga with drill divot

I seemed to have the best results as far as a balance of good penetration and appearance (no pics, POS camera....remember the lug bolt pic?) with the 5/16" attach hole in the 18ga metal, and an approx. .060" deep drill divot in the 12ga plate. BFH tested it until I got tired of smacking it, and it held great. Never got the weld to break, but the 18ga started to fatigue around it. I'd go into a little more detail on the other size holes, but I've got to get in the shower and get my ass to work, besides they were just runner ups of the BFH smack down contest held recently in my garage.....Bring it on!

I'm gonna practice that attach hole/divot configuration a couple of dozen times before I start BBQ'n the car.

Thanks again for all of the tip guys!