I'm about to replace the front (trunk) pan and figured spot welding would be a good way to secure the piece. The only spot welders I've seen look like a big set of tongs. You must contact both sides of the material for this device to work. However, with the trunk pan, you cannot do this...one side at a time.

So...is there a spot-welder that works from one side?

Or, should I just forego the spot welding idea and do traditional welds?

I don't know about a specific spot welder that works from one side, but you can do spots with a wire welder. I'm not sure what a replacement pan looks like, but one thing you might do is cut strips of metal (the same thickness of your replacement) and bend them so that they match any angles you might have at the seams, then apply intermittent welds along the strips. That way you don't risk burning through the edge of the replacement pan or the body of the car.

Can you post pics? Those would be helpful in giving you a better idea of how to replace it.

I already have a replacement pan. I cut it out to match the opening of the hole in the car, with a 1/2" lip all the way around. The replacement drops in & matches up nicely.

My mig welder has a cup that is useful for spot welding. Basically the tip has some big scallops to allow gas to escape. The machine (lincoln 250mig) has a spot weld and a stitch timer setting though you could do this through the "1 mississippi, 2 mississippi" method if your machine has not that option. Since I'm learning to tig with my exotic $200 dollar Harbor Freight tig I've used this to do some spots and it actually works much better than I thought with very little to grind. Of course it requires me to drill through the first piece of metal to have a nice looking job, but its doable without the drilling, just taking more time to melt through the first piece of steel.

In that case, I'd recommend intermittent welds, about 1.5" long each, spaced 4-5" apart.

OK. I was thinking closely spaced spot welds & seam sealer for a nice look (and less grinding).

Didn't think of that...Punch holes thru the top piece and weld through the hole into the bottom piece. That'll work.

If you can track down a June 2007 issue of Excellence Magazine, I wrote an article about replacing the rear trunk and other areas that need welding.. Basically leave a 1/2" lip in existing, punch holes through the new piece every 2-3 inches around the entire perimeter, set on top of the lip and use a MIG welder through the punched holes.

There is an air tool to do this... I believe it is a punch crimp tool... I have one works real slick. Use this and then you basically have a "spot weld"

If you don't have the punch, just stitch weld it into place. Weld from under the car and you won't even see the weld marks. Minimal grinding required. Cover the lip with some seam sealer, and you are good to go. A lot faster to do this then to drill (or punch) 50 (or hundreds of) holes around the perimeter and then fill them in with weld. How big is the patch you are welding in?

Zach

If you really want a panel spotter do a search on ebay for Lenco. I have an old Lenco panel spotter. In most cases this is completely not nessesary. I sometimes I need to replicate the factory look but mig welds are often stronger and sometimes I hide some in the repair for peace of mind.

If it's done right you get both a nice look and less grinding...

drill 1/4 in holes all the way around the edge of the replacement panel about 1-1.5 inches apart. Be consistant in the spacing.

Use the mig welder to do what is commonly called "plug welding"
Basically you have laid the panel with the holes in it on top of the 1/2 inch lip. You start your weld in the center of the circle and rotate in spiral to the outer edge.
If you do it right, once you grind down the weld you either can only see a 1/4 "spot weld" or you see nothing if you sand it smooth.

I have also done this from below (which sucks) but it hides it from about.

Rich

What everyone is describing is a common rosette welding technique.

http://www.google.com/search?q=Rosette+Wel...amp;rlz=1I7GGLG

I'm just replacing the very bottom of the front trunk area (18" x 20"?). I figger 1 spot weld every 2" or so should do it. So...10 spots per side?

Factory spot welds were a weld roughly every 1/2 inch on center. Some were much closer. Some farther. but I have not seem them 2 inches apart.

I'd want that area to be more secure rather then less. it is getting stress from the front suspension and stress from whatever load you are putting in your trunk.

Zach

These 2 gizmos can make the hole punching faster and won't leave the burrs of drilling.

http://www.harborfreight.com/cpi/ctaf/disp...temnumber=91510

http://www.harborfreight.com/cpi/ctaf/disp...temnumber=41696

Thanks! Now I have an excuse to buy new tools...