I am welding in new floor pans in a 59. I have them installed and I overlapped the metal about 1/2". I have stitch welded (short bead about every inch or so) them in place both on the top and on the bottom. The fit is good. I am sure they are structually sound.

So do I grind the stitch welds some and put a seam sealer on the seam or do I need to weld 100% of the seam?

 

Walston;

I butt welded my floor in my '50 F1; I welded solid and ground the entire length of my seams. Probably not required, I then seam sealed the outer (under cab floor) then primed. I used body filler to "beautify" the inner cab floor. On a lap joint I would be concerned about moisture getting between the pieces, but sealer should prevent that. I'm probably going to go with sealing product on the outer cab floor after paint.
Good luck with your project.

Tom

 

Speaking of floor pans, eventually I will be replacing mine but want to keep the rig sqaure. I can see if I remove the can and then cut the floor pans out that it could easily get outta square. I was thinking of building a wooden jig to mount the cab to. Bascially recreate the frames mounting points only on wood. Will that be rigid enough to keep the cab from getting catty-wampass on me? Or do I need to tack weld in some metal temporary cross members? I have see a few of y'all have more more complicated jigs, but I don't have much room and was looking to keep it simple. Thanks

 

If you plan to replace the entire floor I would definitely weld in some steel bracing first. 1" square tubing is the material of choice. add diagonals between cross pieces, at least one in each direction to maintain square. If the floor is very rotted, be sure the cab is actually square before welding in the bracing.

 

ditto on what AX said, brace the cab well with 1" tubing; I think I have some pics in my gallery. The other thing to watch is warping, as always due to heating of floor patch. I have a slight "oilcan " in mine which I may deal with before final paint. I used 14 ga steel, I'm currently working on modifying the tranny cover after Lokar shifter install.


Tom

 

oilcans or "pillows" are usually the result of heat shrinkage along the weld seam. There are a couple of ways to deal with them:
1. Hammer stretch the seam back to it's original length (actually width, the shrinkage is across the seam) use a steel dolly with a slightly rounded face and a body hammer with a slight crown and rounded corners. Push the dolly solidly against the seam and tap (NOT POUND!) the seam with the hammer directly over the dolly. You should get a ringing sound. overlap your hammer taps as you move around the entire seam evenly.
Repeat this process as many times as neccessary until the oilcan flattens. DON'T try to remove it all in one pass by hammering harder you'll just cause warpage. Work slowly and evenly around the seam.
2. heatshrink the center of the panel to remove the oilcan. On a long narrow patch you may need more than one shrink down the center of the length. Do not overlap or try to shrink the same spot twice.

 

So do you think I should weld 100% of the seam on both sides?

 

My suggest is to weld it 100% if you can do it without warping. Also, I apply body sealer after priming with epoxy primer. I like the metal sealed under the sealer. Most body men epoxy primer areas before applying body filler because the epoxy bonds better to the bare metal than the body filler so I use the same thought when using sealer. I also like using paintable silicone sealer, make sure it says paintable or you're going to be in for a lot of problems.

 

I would weld it completely, at least on one side. do go VERY slowly no beads longer than 1/2" allowing each to cool completely before adding another within 4 feet. Yes, it will take a long time, likely a couple days, so have something else to work on so you don't rush it. With overlapping panels there is no way to hammer stretch out any shrinkage so it's "doubly" important to heat as small an area as possible. I would use seam sealer to seal the tacked side, but would recommend one of the 3M products designed for body work and follow the directions on preparation and application religiously.