Welding Floor Pans. Flux Or Gas?

I just ordered new floors and floor supports for my 66 cj5. I’m a novice welder and want to know what setup I should use for my MIG welder. Flux core wire or shield gas? Or is there something else I don’t know about? Any tips will be appreciated.

 

Shielded gas will be easier for you. Flux core wire can be used but you have to constantly clean it.

Use a smaller wire size and practice, watch some videos. I’m sure others will give some really good tips.

 

Definitely gas if you have the choice. Aside from the aesthetics, flux core likes to be run a hair hotter to achieve the same weld. That's not beneficial for welding thin gauge steel.

 

Complete hack here. I tend to keep a grinder handy to beautify my work once I'm done.

shielded is how I'd go about it.

Also, get the thinnest wire your machine will support. 025 or 027 is what I've used on mine. If you have a couple of pieces to practice on, that helps get your heat and feed settings dialed in.

then when actually welding on the sheet, use 'death by 1000 dots', don't just run a bead starting at X and going to Y. that tends to warp things. Do a dot (say a 1/4 inch or so, then move to cold metal, do another 1/4, etc.). You'll find the right size dot for what you're working on. I like to do a few dots (just burn a little blop where it belongs, then move around and repeat a few times so if my clamp gets bumped, I don't have to start all over from scratch with trying to align things again, also, as you weld, the metal will contract/expand and having a few control 'dots' seems to help. (I don't know if this is SOP with the folks that do thin stuff a lot, but it works for what I've done so far).

I welded a washer at the end of cracks in the sheet where possible using similar death by 1000 dots around the circumference. Same on how I filled in the radio antenna hole (grinding smooth when done). (same on the stress cracks on the fenders and grill, I tried to drill the end of the crack, but often the crack was longer than I'd expected.) . I repaired the rear quarter where the spare tire mount was ripped out, then buried under 1/2" of bondo by the PO. I pressed it out with a bottle jack where possible, then used A LOT of wire to fill in the rips and dent, welding, then grinding, then welding, etc. until I was able to live with the amount of bondo required (similar to how folks used to used lead to fill dents I guess).

I tried flux on the sheet metal, it was difficult to control, and the spatter was a PITA, but I might have been doing it all wrong. I tried it on the frame too, same result with splatter, so I've stuck with shielded, less mess, looks great.

 

Agree with all above.
Definitely shielded gas.

If you wanted to you could also have a bucket of water and a rag handy to cool the weld down as soon as you raise your visor which helps control distortion.
Not as important if you will only be spot welding the new floor pieces in but if you end up doing panel repairs it is helpful.

Also, if you have to fill holes because of damage during the removal of old floor, a piece of copper held behind the hole helps prevent the edge from being blown away.

 

a blast from the air hose works just as well with no accelerated rusting. also skip around the panel dont just work one edge at a time

 

Gasless MIG wire is for outside use on fence posts or other junk that needs to be glued together. It should never be used on anything of any value especially on a vehicle. Get a bottle and regulator and do a little practicing. An auto-darkening helmet is a must on thin sheet metal.

 

Smaller wire and gas for thin sheet metal is my preference. And, when possible, I clamp some heavier plate (steel when spot welding, copper when butt welding) behind the weld area to absorb heat and keep the sheet metal cooler.

 

Wow................most important! ..................Clean your metal........the cold rolled sheet metal you'll probably be using for flooring has an oil finish applied during the rolling process to alleviate rust.......and I would use cold rolled. Hot rolled has a blackish grey carbon finish on the metal from the rolling process..........in either case the welding of either product without first cleaning will make your welds look bad from contamination.

This cleaning process also goes for the existing portions of floors that you are attaching the new metal to.........paint , rust & oil must go! ...........those areas should be ground clean with a 100 grit disc and wiped down with acetone prior to welding.......once finished if painting is a ways off.....take some WD-40 on a rag and wipe those exposed areas and remember they will also need cleaning prior to priming and paint............Good luck!

 

A tip for filling holes. Get one of them cheap Harbor Frieght step drills and use it to clean up to a known diameter any holes you have. Then if you have a metal cutting bandsaw or access to one. You can cut a thin piece off of some round stock the diameter of the hole. and weld that in as a plug. Works really well. Run a grinder across and smooth it down. Also get yourself a piece of flat copper to use as backing for filling voids or cracks. Even a piece of copper plumbing pipe pounded flat will work.

 

I just did this on my jeep. I used gas. The flux core wire seemed to spatter more.
Im a novice welder. My one suggestion i can pass on, make sure the old metal is CLEAN. i went after the welding with just light wire wheeling. After tacking the new floor pans, it was a bear to clean the old metal. Clean all sufaces to be welded up before tacking anything into place

 

I agree with everything said above, just wanted to add my two cents, I use Argon mix gas, less splatter. Clean, clean, is the big thing, Stitch weld and move on, don't stay too long, zap move zap move zap move, this will keep from building up too much heat, and distortion. After everything has cooled down you can go back and stitch between first stitches if you feel that you need too. Works for me. Good luck.

 

Thanks for all your replies. Did y’all but joint all floor pans or any lap joints? When lap joint did you weld all the way around or leave gaps.

 

I was just recently made aware that these slick little units existed. For backing up those pesky little holes, hands free:

Magnetic Hole Plug Welding Tool

 

Whatever works for you...........much easier to lap the panel over to weld , but may not work everywhere.......in order to seal the floors you can stitch weld first and cool and come back and fill the gaps....butt joints can be hammered with a dolly..........the parts your putting weight on may need to be fully welded........hidden portions not so much........If your concerned about keeping it water tight............lots of good undercoating / sealer type products out there that can be applied to joints later.

 

Gas. Spot weld and move around the panel. Just keep jumping from one side to the next. Don't make panel get overly hot. If you are doing a full floor panel. Do about a 100 spot welds, then grind them back. Do a 100 more, then grind them back. Etc until panel is in there and looks good. Keep a couple body hammers close by. A pick hammer type in a pointed and flat work good for keeping material tight at the joints between welds. you can also use a broad screwdriver to apply force at the weld joint to tighten it up while tacking it.

Or you could jump into 21st century tech, use a SEM or 3M two part epoxy and then seem seal the overlap. If quick and dirty were your priority, I'd go this route. You pretty much have one shot at it though, so panel pre-fit is paramount!