The Stovebolt Site Forums The Shop Area Paint and Body Shop Cab floor welding, lap welding or butt welding?

Hi all

I am going to have to do some floor repair on my AD, I was wondering if lap welding or butt welding safer for a newbie welder like me.

Any advise and if anyone have pictures of their work will give some idea.

Thanks in advance

Ganesh

This has been talked about in the past quite a bit, I'm sure a search will give you lots of good info.

My personal experience has been to do some of both. Lap welding will be easier for a newbie as your panels don't have to line up perfectly and you'll have less chance of burning holes. You'll need a flanging tool to do it properly. I picked up a cheap air flanger and it works great. Any lap welds I did were seam sealed both sides so no moisture can get in to start the rusting process again.

Butt welding requires careful preparation and trimming of panels to ensure a perfect "gap" to weld. Its lots more work ( and harder to weld) but when done properly ( with welds ground smooth) you shouldn't even be able to tell where the weld was made.

On the cab of my 66 I probably lap welded 75% and butt welded 25%. The factory lap welded ( with spot welds) lots of panels so GM must feel its ok.

Make sure you don't run long beads or you'll warp everything with the heat. Make small spot welds an inch or so apart and move around so things don't get too hot. Slowly fill in the gaps with more spot welds and keep moving around and letting things cool down. Once you start a nice bead you'll get the urge to keep going but don't! Take your time and do it right. Practise on some scraps first to get your welder set up before you start on your truck.

Dave,

Good advise, see I have flange tool picked up from HF and it has punch also to make hole, but after I finish lap welding, should I grind off the bottom piece or leave it like that?

Thanks again for you advise

Ganesh

No you don't need to grind off the flanged portion. Just get some tubes of seam sealer and cover the joint ( both sides ) with it to keep moisture out.

Thanks Dave again

Ganesh

A lot of it depends on your expectations of the finished project. If you are building a show truck, you will want to butt weld and grind and fill both sides. My purpose is merely to fill up the hole. I sometimes don;t even use a flange tool. I cut out the rusty part, fit the floor pan over it, and weld it. I then seal the edges with silicon. The floor mat covers it anyway.

Crenwelge

I think I saw your cab welding pictures, did you use tig welder or mig and I think you changed the cab corner and did some butt welding right.

Ganesh

Although we have a water cooled tig on our 440 Trailblazer, I myself never use it. 45 years ago I used gas and coat hanger wire. About 20 years ago I got my first Millermatic 200 and ran 030 wire. I now have a new toy that I keep at my house. It is a Hobart 140 and I run .023 wire with CO2. The thing is just unbelievable on thin stuff. I have a vice grip type crimper and an air operated crimper, but I seldom use them. I always manage to distort things while crimping. On rather flat areas, I lay a 1" strip of 14gauge behind the splice and hold the 2 pieces together with sheet metal screws and fender washers. I like about an 1/8" gap between the 2 panels and put a screw about every 2". I make about 1/2" stitch welds between the screws and then remove the screws and stitch weld until it is all is welded. Not much grinding or warping that way. But again, on something like a floor, I usually cut out the rusty spot, lay a patch over the hole and weld. The floor mat covers the splice any way. If I wanted it to look pretty from the bottom, I would butt weld it.

The type of weld being done honestly depends on the extent of the repairs your are going to make. If you just have a few holes I would simply cut out the bad metal and replace with either butt or lap weld.

If you have an extensive amount of repair then you probably should get a floor kit. I used an aftermarket floor kit with a transmission hump built in and it was fairly simple to cut out all of the metal in from of the seat and replace the toeboard and front floor pan. Putting in screws first helps alot to keep the metal in place.

Hi, Ganesh,

I did most all of my patch repairs using butt welds. I used some lap welds on the floor in some spots but did not care for how hard they were to seal from the bottom side.

I did not think the butt welds were really that hard. I did get better at it the more I did. I also use a MIG with 20/80 gas with .023 wire, I think. One thing I learned from someone here is to use some copper backing on your butt welds. I have some thick copper roof flashing that I use. I clamp it in and fill up the gap about 1.5 inches at a time. I go left to right and stop and do left to right again back tracking over what was done. That way the piece stays cool. I have some 1/2" thick copper buss bars I use to as a heat sink. They work great. At any rate take your time, practice on some scrap, watch out for the heat and try not to breath the smoke you generate.

You know thanks for saying that for using copper backing, I really think it is a great idea and I am going to go with that idea as well

Ganesh