I am finally about ready to order my new floorpans. I have been reading volumes on welding techniques lately. I find it all helpful, but am still up in the air about which direction to go in. So, I am asking your opinions about the best method to use. I have read about (and watched videos on) plug welding, butt welding and lap welding. I am leaning towards plug welding especially after seeing a vid on youtube where the guy used what he called a 'spot weld tip'. It seemed pretty straight forward and simple (I AM A NOVICE). However I searched the web for that tip, but couldn't find it. I have plans for plenty of practicing on some pieces that came off the car during disassembly that are no longer usable. Anyway, I would like the honest opinions and helpful guidance from those who are familiar with these techniques, preferably those who have used two or more and so have an educated preference. I have a mig welder and lots of time to practice. Please tell me what you think.

Thanks!

 

Use butt welding where you can, lap welding where you can't butt weld and use plug welding where the factory used spot welds. The bigger question is what kind of welder are you getting. 120v mig with gas is what I recommend. Don't go cheap. A nice lincoln or miller would work for you.

 

don't settle in on a method for welding. each application will have its own set of best techniques.

try and duplicate what the factory did. if the two pieces of metal were spot welded together then use plug welds. if you are cutting a patch panel then butt weld new metal back in.

some people will flange metal and weld the seam. i personally feel like this generally will lead to more work. i prefer to butt weld, but butt welding does require more precision.

if you are going to practice, then start with some 20 awg steel. use the thinnest cutoff disc you can find and cut some long slits. practice getting the metal on both sides of the slit perfectly level and then tack weld. watch the behavior of the metal (i.e. pulling together). also look at the penetration on the back side to see if your small tacks are uniform and be sure there are no small pinholes. also practice grind the welds. don't get crazy with the grinding as you don't want to turn the metal into paper. if you can get good a butt welding and finish grinding then most other welding situations will be much easier. take your time. welding too fast will cause you big headaches later.

i'm sure you have a gas welder with some 23/25 wire, if not you are starting in a hole. and i'm sure you have a nice body hammer and dolly.

what is this spot weld tip? does it hook to an arc welder? i'm not aware of anything for a mig, but i'm not a professional.

 

Thanks for the pointers guys. At times like this when I am a complete novice I prefer to admit my ignorance and listen to others who have experience. Thanks.

My welding setup is a Lincoln SP-135T with gas. I think this should be adequate for the work I will need to do on the Mustang.

In regard to butt welding the floorpans, I undertsand this to be the more desirable method as the pans are simply patching what will be cut out of the original floor. My fear is more in getting the required fit than in the actual welding technique. Having never attempted this before I am dubious of my ability to cut with enough precision to produce the appropriate fit for this technique. That is pretty much why I was leaning toward the plug method, seems like it would be more forgiving of my inexperience. This is the name of a youtube video that uses that 'spot weld tip': (1971 Olds "S71" Plug / Spotwelding Tips V8TV). Copy and paste this into the search bar in youtube and you'll see where I got this idea from. The guy talks about it starting at about 3:08. I had put the link in but it loaded the vid right into this post and I'm not sure if that is kosher on this forum, so I put the name in instead.

I'll keep checking in for more input.

Thanks again.

 

I'm a novice welder too - can get by - but welds are not the best. Butt welding is tough for me - tried a couple times and advoid it now. Nice thing about floors is between seam sealer and carpet you can a hide a lot. Good place to start out.

 

don't mess around with the "spot weld tip". it's a gimmick and only acts to create a gap from your tip. nothing special. if anything it just makes it so you can't see what you're doing. you have a much higher probability of missing the hole or burning thru than normal.

are you putting in a one piece floor or pans? are there any other rust areas that you could do surgery on before doing a floor? small patches end up being the same process as small patches with the exception that the large patches just take more time.

if you are doing floor pans, i wouldn't just plug weld the seam where the old floor meets the new pan. weld the entire length. of course the floor pan to rocker you would plug weld.

if you decide to flange then make sure your flange is pointed in the right direction. you don't want to trap water in a pocket.

consider welding the seam on the underside of the car. i've seen people weld the seam on the inside and of course the carpet hides the fix, but peak underneath the car and you see a flange and can quickly tell a repair was made.

the key for me to butt weld, is getting a small gap and making sure the metal is level. that way when you grind you don't take any necessary metal down.

you can fit up metal relatively easy by trimming it close and use some sheet metal screws to secure the overlapped metal together. then using a body saw or thin cutoff wheel, cut thru both pieces of overlapped metal. peel the metal back, get the metal level and tack. do this along the entire length.

 

GREAT! You're using gas. Don't EVER try doing bodywork with flux core.

Regardless of which joint you pick, don't take off and start running a bead. Jump around all over with a little weld here and a little weld there. This will prevent warping from excessive heat in one area. Get an old fender or hood, cut it and practice welding before touching your car with the welder.

 

Couple of small techniques that helped me allot. Normally a plug weld uses a 3/8" hole, reduce it to 1/4". This reduces the heat-effected-zone, and minimizes warping. Round your corners when cutting if possible, this will reduce blow-thru at the corner. A good tool to have is an Eastwood magnetic plug weld tool with a copper face (#29935). Last, the cleaner the metal, the better the weld! Make sure you grind aware all oil, rust, paint, etc on BOTH pieces before you weld. Watch your voltage...practice on the lower side, and work your way up until you have good penetration without blow-thru. You'll know when you have a good weld, the hardest part is consistency.

 

I would plug weld over the frame rails using at least a 3/8 hole and lots of heat for penetration. The rails are a lot thicker than the floor pan and you need a strong plug weld.I would space them out about every 2 inches. When overlapping I would give 1/2 to 1 inch.Weld it solid top and bottom. Remember it is a unit body car and the floor is an integrial part of the strength of the car.Bad welds do crack when the car is in an accident,I have seen them many times in my trade.Inside the car,I would make the welds strong before beautiful,since it is covered with seamsealer and carpet anyways.

 

Well I must say that I am pleased with the responses to my dilemma. Although there is some disagreement on preference of welding style and on technique for each style, that is exactly what is helpful. Those who have real opinions always seem to have good reasons for those opinions. Very helpful indeed.

Buckeye: The last part of your last post really made me reconsider the butt weld method. That makes perfect sense and it pretty much eliminates what was my biggest objection to that style, that being of somehow cutting the perfect gap. Such a simple answer to what had me boggled. Thanks very much! I'm not terribly concerned about anyone discovering that floor work has been done as this car is destined to be as nice a driver as I can make it. I'm more concerned with not screwing up what is going to be my biggest challenge. Engine, trans, suspension, brakes, all no sweat, very familiar with this stuff. Welding is a different cat. But I hope to get good enough working on the floors (which are mostly out of sight) to be able to do a really good job on the stuff like fenders where butt welding is the only real choice. I'll have to see if I have the guts to butt weld the floors.

Groho: Have you used that Eastwood tool? I looked at it online and honestly could not make heads nor tails of it! Tools that will help if I go the plug weld route are appreciated. Maybe that could be used for Mike Tucker's input on welding to the frame?

Mike: I read your post twice to see that you are talking about plug welding to the frame and lap welding to the floor remnants. That makes sense to me as I believe the factory spot welded to the frame? Doing it by combining plug and lap welding would make it more 'factory' I guess. I'm assuming you're suggesting welding it both inside and outside of the car, "top and bottom" as you put it? Must admit I hadn't thought of that, it would double the work for sure. Is it necessary do you think, or just a good idea?

Again, thanks to all who are giving their input. It is very helpful as I am learning a lot.