MIG Burnthrough question

How big is your wire? That might need smaller wire.

Gunner

"At the core of liberalism is the spoiled child - miserable, as all spoiled children are, unsatisfied, demanding, ill-disciplined, despotic and useless. Liberalism is a philosphy of sniveling brats." -- P.J. O'Rourke

Wire that I'm currently using is .023"

One thing that I forgot to ask. Where I have the most problems, I tend to have a gap between the pieces that I am welding. What should the gap typically be for thin sheet metal?

Thx!

Use a small wire diameter in your MIG welder when working with the old metal. It'll be easier to control and less likely to burn through. We typically use .025 or smaller wire when we do sheet metal restorations on old cars. Also, running a bead is generally a bad idea, the metal gets too hot and will burn through. We use a series of small "spot welds" with the MIG welder.

We work around the patch on opposite sides. I.e... Spot on the left side seam. Spot on the right side seam. Spot on the top seam. Spot on the bottom seam. This way the sheet metal won't get too hot and warp or wave, nor will it be inclined to burn through as well. Just keep on adding in small welds until you have done the entire seam. Don't be in a big hurry. With old sheet metal cool is good. Slow generally means cool also.

If you have a particulary disagreeable spot to fill in, we also use a copper backing plate to act as a heat sink and support the weld metal until it cools. Let me know if you need a backing plate, we sell them for $9.99 plus shipping.

Hope this helps, James Walsh Jr.

My old Dan-Mig welder has a "stitch" mode, which has been a life saver for me when doing thin stuff. I tend to still think like a stick welder " MO Power!!" and then spend way too much time filling in my burn throughs...sigh.

I can set the length of time that the arc burns, then it shuts off for an adjustable length of time, then back on, then off etc. This allows me to move over some distance before the arc starts up again. Works slick for a ham handed dauber like me.

"At the core of liberalism is the spoiled child - miserable, as all spoiled children are, unsatisfied, demanding, ill-disciplined, despotic and useless. Liberalism is a philosphy of sniveling brats." -- P.J. O'Rourke

I used to braze new metal in when replacing rusty metal in cars. Brazing is a lot lower temperature process than welding and once you get good at it, works great for this.

Bob

All - Thanks for all the useful info. Since I'm working in areas that are part of the unibody, inner rocker and floorpans, I'm not sure if brazing would work.

For the door jamb, that sounds like it would work.

The method of spotting in the panels sounds promising as well. I'll give it a shot!

Steve

Brazing is less mechanically strong and isn't an acceptable repair on most of a monocoque. Here in the UK it's an inspection failure to see visible brass. The rule came in a few years ago and was applied retrospectively, so many past repairs became unacceptable overnight.

Of course paintwork or taking your car to Blind Bob might avoid this, but it's still a hassle.

Butt the pieces tight, with no gap whatsoever. Penetration isn't going to be a problem with thin sheet metal, whereas burn-through is, as you have already noted. It's the gap that is causing the problem.

Randy - Thanks for that added info on stickout. I'm fairly new to welding, so there are a number of things to learn. I had an experienced welder work with me for a few weekends, but there is so much to learn that you can't read about!

Also, I learned a bit about brazing. There was a hole in the cowl, that I was able to get a small oxy/map gas setup from the local hardware superstore and used brass to seal it. Came out rather nice for a first timer :)

Again, my thanks to all of you who have responded!

Steve

This is true for steel your welding but not for aluminum. You can't pull increase stickout much so amps are not reduced much and must be close to correct setting. With my Lincoln SP125+ I only had burn through problem trying to use .030" fluxcore wire on 24 ga steel. Could only weld using long tack welds or pulsing. But, it was easy with .023" or .030" solid wire and C25 shielding gas. Some small MIG welders have poor low end and must use .023" wire for 24ga steel. The real bad 110V MIG welders will have hard time welding 24ga steel even with .024" wire. Maybe the lowest voltage tap outputs too high voltage or needs more inductance. What good is a 110V welder that can't weld thin body metal? Even Miller has made some 110V MIG welders with this problem.

Gee it worked for me on our aluminum gun... 300 amp with a push pull gun attached. Of course like steel you risk losing shielding. 110 machines I realize are a breed unto themselves. Randy

I just cut and tacked some patches on a jeep wrangler recently. I used

16gg steel i had laying around and had the same burn through woes. The problem is that the old steel gets very thin once you grind down the rusty areas. I set my mig wire speed to the lowest setting (the wire speed dial also sets the amperage) I did the same for the power (voltage) as well. I started the weld on the NEW thicker steel then bumped the old just enough to tack it. You're going to get some burn through still, you just want to tack the peice into place. Once it's tacked, grind it down and use some duraglass (sp?) filler over the top of that. This filler uses resin and glass in it and it will fill in the small gaps. Sand, then add your filler puddy, then sand... you get the idea. The floor pans were easy because you had more steel, old panels usually are not so generous. Good luck! walt

Could you use a copper plate backup on the thin area and lay down more on top without burning through then it would be thicker... I don't do MIG so it is a 'off the top of my head' idea.

Martin