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Topic Review (Newest First)
05-04-2008 01:47 AM
jnanam i would agree with what many have had to say there are alot of different ways to do it depending on what you have. the way i would probly do it (depending on what the pan or panel looks like is trim it so that you have about 1/4 to 1/2 in over lap. then take your flanging tool and put a crease around the old metal witch will allow the new pan to sit down flush with the older metal and will also give you more strangth and be more rigid. grind it clean and use some weld through copper primer or whatever you like. weld it it (DO NOT WELD LONG STROKES AT A TIME) and move around the panel so that the heat is not all in one area. once thats done you can grind your welds it will look nice. prime then seam seal making sure its pushed into any voids and paint. put your foot in the gas like you stole it and dont worry about kicking the floor out.
05-02-2008 01:09 PM
F&J One important thing in doing these pans is to accurately plot out the depths of the F&R footwells, and the height & location of the seat riser and mounting holes. It is REAL easy to get the floors way too low as you are retrimming to get a good fit to the existing remains of the floor areas.

I put numbered marks along the top of the tunnel and the 2 door sills. Then use a straight edge across each mark and measure down to important features and make a good sketch. (before removing old floors) In a perfect world, the measurements would all come out correct with the new pan, but due to the differences in stampings, a compromise is likely on some measurements.
05-02-2008 12:03 PM
F&J
Quote:
Originally Posted by MARTINSR
This is one thing I disagree with, the 1/4" overlap. My thoughts are, why leave an overlap that is smaller than original, just for the sake of making it smaller?

If you overlap it a half inch, and make it "look" original, there are many people who wouldn't even know you patched it! If it "looks" like it came from the factory that way, I feel that is second best to butt welding and metal finishing it to look EXACTLY as it did before. Which I would do, IF it were a super valuable or special car like a big block convertible or something like that.

But if you look around that floor, look at how the panels are held in, then do your "patch" the same way, make it look OEM.

Brian
The main reason I go with small laps: The repro pans seem to have wrong angles on the sides. As I am gradually trimming the old floor back and test fitting, it seems to fit better with less lap because the 2 different angles will lay together better for welding & positioning. 2nd reason is that when I am done welding the edge of the new pan to the old floor, that small lap is easier to dolly to a flat fit under the car. It actually lays flatter and looks better IMO. If I was using a punch tool and plug welding instead, I would do a wider lap.

Also, on a floor, we are putting a seam where GM never had one, so no sense in using a step flanger to replicate?? Besides, a step flanger does not like all those curves and angles.
05-02-2008 08:11 AM
MARTINSR This is one thing I disagree with, the 1/4" overlap. My thoughts are, why leave an overlap that is smaller than original, just for the sake of making it smaller?

If you overlap it a half inch, and make it "look" original, there are many people who wouldn't even know you patched it! If it "looks" like it came from the factory that way, I feel that is second best to butt welding and metal finishing it to look EXACTLY as it did before. Which I would do, IF it were a super valuable or special car like a big block convertible or something like that.

But if you look around that floor, look at how the panels are held in, then do your "patch" the same way, make it look OEM.

Brian
05-02-2008 06:43 AM
69ChevelleAddict Thanks for the help!
Im not really concerned with looking 100% factory and I'm ok with the fact that people will be able to tell I replaced the floors.
Dont get me wrong I'm not trying to rush through this or anything I just want to have fun and be safe while doing it.

There are a lot of spots where I can leave a little overlap 1/4" or so which I think will help me getting it ligned up.
I just dont want it to rust out on me down the road, spent WAY too much time fixing rot on this car.
05-02-2008 06:08 AM
F&J
Quote:
I guess im asking if there is a structural difference between spot welding vs a full bead of butt weld.
That's sort of a loaded question in this particular situation. In my opinion, for most backyard hobby guys lacking tons of experience, I would go with the lap on those floors.

I did do floor halves on a 68 Chevelle factory 327 4sp. As I recall, the halves fit pretty good, BUT.. you can't expect any repro panel to fit exactly the same as an OEM mint floor panel cut out of a donor car. That repro one would lead to serious problems when trying to get both the car & panel, trimmed EXACTLY for true butt welding. That's why I said "show me how it comes out". I can't imagine trying for a perfect trimming on a full floor half from front to back. These repro pans may sit a little low or a little high in certain spots when you try to line up the sides of the pan where they curve up. Like I said, I keep fitting, marking & trimming both the body and the pan, until I get a decent fit. I may pull the pan out a dozen times for more tracing & trimming. Then you still need to force certain areas of the new pan to meet those curves.

It won't hurt anything to try to start fitting and trimming for a butt weld, but as you get into it, I think you will see what I mean. The pan will fit terrible before you get the trimming somewhat close to an inch overlap. Go for an "inch overlap trimming" to start with, then see how things line up. If it fits really good, trim to a 1/2" then 1/4" lap. Then you will need to make up your mind to either trim to butt, or stay with a slight overlap. I would never butt, but that's me...I'm old, and I need to spend my time on more important areas...that actually show
05-02-2008 05:58 AM
baddbob The structure is only as strong as the metal it's made of, the factory seam has a flange that's bent and adds some rigidity but if your weld is good the strength will be as good as the sheetmetal itself. The 71 Chevelle is a full framed car so I see no problems with doing a butt weld on the floor anywhere.
05-02-2008 05:20 AM
69ChevelleAddict I guess im asking if there is a structural difference between spot welding vs a full bead of butt weld.
05-01-2008 08:05 PM
baddbob If the pan you have is the same as a factory pan then definately seperate the seams and install it like factory with plug welds. But if you're using just patch panels then trim them to fit and butt weld them in for an invisable repair. I have had to install some pans that weren't good copies of the originals, a few have even had the rocker flanges pointing upwards instead of down like original-on these I cut as needed and installed only what was necessary with butt welded seams to keep the original look. It's your car-do it the way you want. Bob
05-01-2008 06:24 PM
NEW INTERIORS
Quote:
Originally Posted by F&J

If you think you are up to the frustrations of butt welding an entire floor half...go for it

But I want to see the results
Here you go!!!!! Some results!!!!
05-01-2008 05:53 PM
BMM Would weld-thru primer and seam sealant on the finished weld not solve the water and rot problem?
05-01-2008 04:49 PM
adtkart If you are going to replace floor pans, atleast do it right. If you think that your but welds are that strong, you better think again. You have to have the panels fit perfectly to get a strong enough weld, specially for the floor. The factory lapped the joints and sealed most with seam sealer. Since most people don't have access to a spot welder to do them exactly like the factory. The best bet is the use of plug welds, done with a mig welder. Apply weld thru primer first, and seam sealer after you are done.

I would not have a car that someone had installed floor pans by but welding them. I would be cutting them out and replacing them immediatly.

Aaron
05-01-2008 04:17 PM
MARTINSR Like I aways say when this subject comes up, the ENTIRE car is held together with lap and pinch welds! There isn't one single butt weld on the car from the factory. EVERY single panel, including the floor that we are talking about is held on with lap welds! Why in the world is one more so bad?

The only reason a lap weld would perform any different than the hundred and fifty other ones on the car would be if it was done incorrectly.

Leave about a half inch lap like the rest of the cars lap welds have.

Brian
05-01-2008 03:55 PM
F&J err..., lap welds are all over that car, and done by GM


I end up trimming the pans to where they fit the best, and lay them in to trace around them . Then, pull out the new skin and trim the old floor to 1/4" lap. That 1/4" makes a heat sink when welding, plus it gives support when you need to persuade some of the new pans edges to fit tight.

If you think you are up to the frustrations of butt welding an entire floor half...go for it

But I want to see the results
05-01-2008 03:37 PM
lets cut it up if done correctly, lap welds will work on floors. Sometimes you need a backing when doing this type of work and a lap weld will work in those situations where a butt weld will not work. When I have to do it i leave only like a half of an inch to over lap. JMO Tim
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