welding burn-through

na2ub · 03-21-2006, 06:30 AM

I am patching a few bits of metal around the bottom of the door sill, an am having trouble welding the new patches in because the metal is so thin. I matched a piece that I cut out for thickness, which turned out to be 22 guage from the local hardware store. It is the actual existing body work, though that I am burning through. I am using a Lincoln Pro 100, on the lowest setting. It recommends that I use solid wire and gas (MIG) for metal this thin, but I don't currently have it set up for that, and I use flux core. Will solid wire and gas help that much? I know it makes for easier welding in general. Any other tips, all the metal in this area is really thin.

Doug

Rot 911 · 03-21-2006, 06:37 AM

You need to switch to solid wire and gas. Try to find some .022 or .025 wire. Make small spot welds moving from one area to another until everything is filled in.

RickM · RickM's Garage

Looks like you're bound by the capabilities of your equipment. This is where Argon or C02/Ar will keep the splatter down and help create an overall cleaner, nore controllable weld. But also remember that the variability of the welder output and feed is very important. With most inexpensive welders you have 3 - 4 general settings.

FWIW, I'd probably be going with a heavier gauge steel as well. Probably 18-20.
In my experience I've had luck concetrating more of the weld on the heavier material and washing over to the thinner.

Jon Merck · 03-21-2006, 06:48 AM

I am no expert by any means when it comes to welding, but I have tacked a backer piece in place to prevent burning through and it worked for me. I don't know if your situation will allow the backer piece. Hope this helps!

Kemo · 03-21-2006, 06:54 AM

flux core at .35 or .3 wont work well on the thinner stuff. after trial and error, I also found out that you need to make sure you got a real good connection at the wall. I was on a 20amp and was having a fit. Finally plugged directly into the wall (no extension cord) into a 30amp plug and it was like a new welder.

I have the Campbell Housefeld Farm 110 with std plug btw. I was able to get better welds with the .30 flux core, Im a hack, but I have a really good instructor.

If you can stomach the money, go to the gas setup with even thinner guage wire. I dont know how much thinner you need to go, but Ive heard its night and day. Kurt V is saying what alot of other guys that weld alot say to me. I think that would be a good place to start if the .30 flux and the better power source dont help.

fuelie600 · 03-21-2006, 07:04 AM

You can also hold a piece of copper behind the areea to help with burn through. I use a piece of 1 inch copper pipe joint when I do a delicate area.

The right gas helps alot....

widebody911 · widebody911's Garage

I 2nd the copper suggestion. I use small sheets of 1/8" copper that I got at a local surplus yard.

Rot 911 · 03-21-2006, 07:14 AM

I didn't mention using a copper backing plate (which really works well) due to the fact that he is welding the bottom of the door sill and I can't think of a way you could get a copper backing plate in there and be able to remove it when you were done welding.

na2ub · 03-21-2006, 07:28 AM

Correct, Kurt. I can't get any backing in there. I suppose I will have to get my gas set up, and use solid wire. Not a bad idea about using thicker metal, too, and puddling it over. Welding thin metal is such a pain!

Doug

john walker's workshop · 03-21-2006, 07:46 AM

spot weld only. no continuous beads. sheetmetal welding with a mig is just a series of overlapped spot welds. first, position the piece in place with a spot every inch or so, then do a series of spots for about 1/2 inch from each original spot, moving around from one area to an opposite area to keep the heat down. don't cool it with a wet rag, because that can cause more warping than the original weld. let it cool by itself, then weld more. a bright light behind the panel will show pinholes which can be spotted closed.

na2ub · 03-21-2006, 07:51 AM

Cheers John, I will give that a try.

Doug

na2ub · 03-27-2006, 09:15 AM

As per JW's suggestion, the spot welding tecnique worked really well. I was actually adding metal each time, rather than burning holes. Follow up question, what is the best tool for grinding down welds. I noticed that the weld beads are really hard metal. I have a "personal" compressor that is 25 gallon 5 hp, or something like that, so I don't think it can support tons of "continuos use" tools. Should I be looking for a die grinder with stone tips, anyway? I always see the "pros" using a angled die grinder with a flat pad, but I would need to get into spots that would not make that possible.

Doug

john walker's workshop · 03-27-2006, 09:23 AM

the best tool for dressing down the weld bead is a makita hard disc grinder. thick 4" discs. they just hit the weld and not the sheetmetal around it, at least until the weld is flush. then i finish it with an air angle grinder using 2" twist-lock 80 grit and finer flex discs. be careful with heat, just like welding, as you can warp just fine with a grinder.

wcc · 03-27-2006, 09:29 AM

na2ub,
Did you end up switching to a solid wire with gas? I did a similar project with a Hobart Mig welder with fulx core wire doing the spot welding technique and I still burned through. I ended up using a friends Tig, but I was wondering if you switched to the gas and solid wire.

RickM · RickM's Garage

Be careful with the sparks that fly off your grinder. The metal debris will damage paint and pit glass. Best protecting those areas.

911SCfanatic · 911SCfanatic's Garage

as usual, what JW said is gospel--except I prefer my DeWalt grinder.

Zeke · 03-27-2006, 09:45 AM

Quote:

Originally posted by 911SCfanatic
as usual, what JW said is gospel--except I prefer my DeWalt grinder.

Yeah, why the Makita plug?

I have a Makita in my work truck and it's been there for 20 years. Tired of going to the truck every time I needed it in the garage, I bought a Harbor Freight 4" grinder thinking it would last a week. That was 2 years ago. $19 goes a long way in China.

For really thin or questionable metal (read rusty on backside or contaminated with lead or brass), you can use an oxy/acet outfit with a no. 1 or 2 tip and do the same; weld a little, wait a lot. You can also go back over ground down welds that show pin holes with the O/A setup and use brazing.

Maybe rewelding with the MIG is faster, but the brazing sands down quite eaisily if you've already gotten things relatively smoothed out.

Airfinn · 03-27-2006, 10:07 AM

Doug,

You'll find that solid core used with straight CO2 will be a cooler weld, though produces more splatter. However flux core, with 80-98% Argon and 2-20% CO2 (depending on what you have available in your area) will give you better penetration, less splatter, but more heat.

Good luck.

na2ub · 11:30 AM

Bill, I did not switch to solid wire. That was a last resort as it would cost me 100s of $$ to do so. The spot welding worked nicely and, as I said, added metal rather than removing it. The metal is really thin though, 22 gauge, so my results are a big messy bead of lumps. (Or lump of beads?) As long as I can coat it and protect if from future rust, I am good to go. I wanted to grind it down, even though this is on the inner rocker, so I could see how well the patch is working. I still need to do one move inner rocker patch, then I will need to patch the actual piece of door sill that I cut out. That piece will need grinding, priming and a spot of color match (rattle can). In a few years I will attempt an overall repaint, so the paint does not need to be perfect now, just the body work.

Airfinn, that is good to know. I am dying to switch to a proper MIG gas setup as soon as I have the extra dough. I suppose an Argon CO2 mix is the way to go. I though all gas setups would reduce splatter, though. Anyway, as an amateur welder, anything that makes welding easier is good.

What's the best way to protect the backside of my patches from future rust, if you cannot reach them / coat them after welding them in. I coated my first patch with a cold galvanizing zinc (95%) before welding it in. Today, I picked up a can of 3M Weld-through primer, but now I am wondering if that will be any better. I guess it will be the same, but help conduct current during the weld, for a better weld. I would love to have a proper "body shultz?" gun, but again, $$$.

I guess the consensus is to get a 4" grinder for grinding down final welds. I am really not familiar, so, can I get one that is air or electric? What type of pads or wheels do I need to grind down the welds?

Doug

Airfinn · 03-27-2006, 11:51 AM

Doug,

Mig generally doesn't like paint or rust, though it will accept a poor ground.

Air grinders are excellent, and smaller to handle, though you'll need a good compressor to keep up. A die grinder with a 1/2" diameter X 1" carbide cutting bit might be another option, but will require lots of air as well.

Lance