Ok experienced sheet metal welders, talk to me! I am a frustrated and ticked off beginner welder trying to butt weld in a floor board in my 72 charger, drivers side. I've burned more holes than expected. Its cold out in the 20's. Lots of questions, first I got spot welding down no problem there however I need to know what welder settings are best in the cold for butt welding. I have tried #2/30 to #2/50. #1/30 is worthless and #3/40 is too scary. Metal gauge is around 20. I'm trying to weave weld back and forth across the seam. In some areas I made bad cuts and there is an 1/16" to an 1/8" wide gap to cross and fill. Is that possible? How do I do it. How do I fill the holes that I've already blown thru? Problem is I can't see the seam most of the time due to helmet settings and physical positioning (dash still in car) Using spot light and still can't see. Got the floorboard spot welded to the frame no problem there. Do I need to weld the whole length of the seams and should I weld both top and bottom of the floorboard. When it's finally welded how much do I grind the weld down? When it was warmer out, in the 50's, setting #2/30 seemed to work decently. Welder is an Hobart 140 110 volt. I'm trying to hold the nozzle as close as possible so air doesn't rush in and start poping. The wire is #23 solid core and gas pressure at 25lbs. Wire starts at 3/8" out of nozzle holding it at a slight angle and still I blow holes. Any adivce will be greatly appreciated. If you want my email respond and say so. Thank you very much Don

 

Here is a video. I hold my trigger a little longer and a non self darkening helmet can help watch the red heat disappear while staying in the same spot before you pull the trigger again. Don't weave.

 

im just outside gloversville

 

I know its too late but why butt weld it? An overlap would be way better and certainly easier to weld. I dont think I could butt weld sheet metal.

 

You need back up metal. Either get some copper and hold behind the seam as you go, or cut some scrap strips and just allow them to weld to the bottom. It's a lot of work, but you can take various cutting grinding tools, and break the backup strips off when done, then grind smooth.

Sheet metal, especially rust compromised, is without a doubt one of the tougher welding jobs.

Grinding it clean will help. Overlapping spots may be the best you can do.

 

My thoughts exactly.

 

Outstanding info and video Coronet 500, can't wait to try again this time with some copper thanks a bunch, let you know how I made out dgbcharger

 

A couple of finer points are breathing and body position. Keeping your elbow close to your body will limit the motion transfered to the nozzle as you breath.

Before pulling the trigger pass your nozzle along the path you plan on welding to see if you snag on anything or get yourself in an ackward position.

As your welding you should find as you pull the nozzle away from your material and extend more wire the weld will become colder.

Good luck, and yes please keep us posted.

 

These guys have pretty much nailed it but I'd like to add a couple things;

Don't weave, just fill the excess cuts and blow thru you want to fill but also move around a LOT so you allow the metal to cool.

Concentrate the heat of your weld to the thicker metal.

You dont need to run a constant bead, Just tack and move, tack and move, tack and move, esp if you've got it welded to the frame rails again.

Lighten the lense on your hood so you can see better.

Get some copper tubing and hammer it flat into a "spoon" on both ends so you can clamp it in place behind your holes and work area, I usually like a piece about 24" in length personally. (Copper wont stick to your steel)

Grind your welds flat and apply a sealant then paint, sound deadener and (jute) carpet.

A butt weld is perfect for what your doing IMHO!

If you lap weld it, you give moisture a place to take hold and then you've got rust-again, whats the point of replacing metal if you're setting it up to rust away, again?!

I can't give you pointers on your welder because I'm not familiar with that particular model, BUT, you want enough heat to penetrate the metal but not so much to blow through and not so little that you don't get penetration.

 

I found it best to use the a fore mentioned copper backing, then see how long you can go before burning a hole. Just tack it a little at a time and move around from spot to spot. When your copper backing gets hot let it cool and then start over. and .23 wire is where its at in my opinion.

 

Thanks to you guys for all the advice, I followed the advice and watched all videos and achieved great success welding my floor board, at least on the inside of the car. Do I now need to do the bottom of the seams under the car???
And while I think of it, my trunk lid has 6 mounting holes in it from a large luggage rack that I removed. The holes are 1/4" to 5/16". Should I try to weld them closed or just glue in backing plates and bondo up the outside. I really don't want to reinstall the rack after a paint job and finding a suitable replacement lid at an resonable price has proven difficult. Any thoughts?? Thanks again

 

We'll, that's a "depends" answer to your question lol.
If your cars body is on a rotisserie, and you can "flip" your body around easily, go ahead and weld the floor pan from the bottom as well, it won't hurt anything, but it's REALLY not necessary.
BUT, if its on the ground, don't worry about it, I just use a seam sealer top and and bottom once my welds are ground flat and then paint or POR etc.
As far as the trunk lid and luggage rack go,
That's where things can get "hairy" REAL quick. If you have a old scrap body panel off another vehicle, drill some various size holes in it and practice your plug welds until you're comfortable.
You must go very slow, using your copper tubing backing, moving around from hole to hole, allowing the metal to completely cool and filling just a LITTLE at a time.
DONT, try to fill a hole all in "one go", you can warp the panels VERY easily, and the last thing you want after it's painted, is "waves" in the body.
Also, grinder heat can cause warpage as well, so take a little metal off at a time till it's at the level you need, don't attack your plug welds with a grinder lol.
Keep in mind, all you're doing is filling a hole (that's what she said lol sorry couldn't resist) plug welding those luggage rack holes are not structural, so easy does it, patience goes a long way.
All that said, I still highly recommend plug welding those holes over bondo!

 

I plug & butt weld sheetmetal & steel using a piece of aluminum strip

 

I have found these very helpful for this kind of job...