Repair small spot in passenger floor pan

[JWMcCrary]

I have a spot of rust in the floor pan on the passenger side that hasn't become a hole yet, it is actually just cracked about 4 inches in length, but it's bad enough water and dirt gets in the cab.. This crack is due to a little rust. I can get back about an inch or so and the floor seems fine. Should I cut this out and patch it or just put a patch over it? Should I weld all the way around the patch or drill a few holes in the overlap, weld up the holes and then seal around it? I have found that if I weld in about 2 inch sections and skip around until it is all welded I do fine, but if I try to weld a long stretch I tend to burn a hole. Is this normal ?

I have stick welded all my life but just now trying to get the hang of Mig welding. I find that if use the wire temp and speed settings recommended in the guide on the machine I tend to burn holes in sheet metal. I can back off a little and it seems fine but the welds are not pretty...maybe that's not important. Any tips? I am using a Lincoln 3200, with CO2/Argon mix running about 12 psi. Any tips would be appreciated.

 

[eds66bronco]

try a sheet of copper held in place behind the patch with a welding magnet. soaks up excess heat and keeps the thinner metal from blowing through. lower the amperage and make sure you are using the smallest wire you can feed. i use .023 for body work.

cut out an patch or you will be fixing a bigger hole a few years from now.

let us know how you make out and good luck

 

[dpmerrill]

ed's tips should get you there. I would also mention that if the metal you're welding is not clean and rust free, it will burn through easier.

Another thing, if you're not doing it already is hold the welding tip at an angle to the steel. If you are pointing it straight at the steel it will burn through easier.

I would cut out and replace the bad steel. It's not doing any good anymore, and the crack is going to allow water to get in between the panels.

As far as the length of your welds, I would weld even less than 2 inch stretches. Too much heat will shrink and warp sheet metal. It might not be that noticeable on floor panels, but you can really see it on body panels. On body panels you pretty much have to do spot welds all the way around the seam.