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TIG vs Spot Welding and Tunnel Weld for 65 Floor Pans

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Old 06-09-2008, 02:56 AM   #1
CalStang65
 
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Default TIG vs Spot Welding and Tunnel Weld for 65 Floor Pans

Hopefully this is a quick question, but I'm getting used to the fact that they never are:

I've cut out the old floor pan on the passenger side and am preping the new pan for welding. Turns out the shop I'm working at only has can only do TIG welds. What are the pros and cons of tig welding where there were factory spot welds? I figure we can weld the entire frame rail to the floor, weld along the top of the connection to the rocker panel and elsewhere. A guy who knows more about welding thought that drilling out holes to simulate some of the spot welds for the rocker panel connection might be a good idea to avoid the two pieces working themselves apart . . . Another option (although I'd like to avoid it) is to TIG as much as possible and then pay a local welding shop to do the spots. Any thoughts you guys have will be really helpful.

And considering there was not originally a seam along the transmission tunnel, have y'all found it better to have some overlap between the new pan and the old metal extending from the tunnel or did you welding then without overlap? On the one hand, the floor would end up being twice as thick in that overlapping area, but it would also seemingly give the new pan a bit more structrual strength. But I'll go with what you guys think.

Thanks as always!

Cheers,

Alan
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Old 06-09-2008, 09:57 AM   #2
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Default RE: TIG vs Spot Welding and Tunnel Weld for 65 Floor Pans

The most common practice wrt the spot welds is to simulate them using a rosette weld. This is as you describe where you drill a hole in one part and make a weld through that hole to the other part. It doesn't matter what welding process you use for this. I've done rosette welds with Oxy/Acetylene, TIG and MIG. Any process will work.

Anywhere you cut something out you want to put the new metal back in to simulate what was there. Already talked about the spot welds. When you cut a piece in two that was originally one piece, like cutting the floor pan along the tunnel, you should weld that line continuously.
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Old 06-09-2008, 10:31 AM   #3
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Default RE: TIG vs Spot Welding and Tunnel Weld for 65 Floor Pans

Preferably with a sound buttweld anywhere that has structural function. Lap welds put a little bending right at the weldand in the adjacent heat-affected zone simply because thetwo pieces of metal are NOT lined up. Fatigue is the main issue, although you're also creating a potential moisture/crud trap. Continuously welding along the "outer" of the bare sheetmetal edges and at least stitching along the inside one would be somewhat better.


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Old 06-09-2008, 10:48 AM   #4
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Default RE: TIG vs Spot Welding and Tunnel Weld for 65 Floor Pans

I missed the part of the question regarding overlap. As Norm said, a butt weld would be best but having an overlap is fine too. The overlap also makes it easier to actually get the pan to fit because you can use sheet netal screws to pull the pieces together before welding. Once welded, remove the screws and weld the holes shut. Like Norm said if you overlap, you can weld one side of the lap continuous and then put some stitch welds on the other side. Lots of cars done without this step though. Use seam sealer wherever the overlap is not welded.
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Old 06-09-2008, 01:16 PM   #5
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Default RE: TIG vs Spot Welding and Tunnel Weld for 65 Floor Pans

Thanks guys, this is all incredibly helpful. I'm going to pass along all this to the guy whose helping with the welding and if we have more questions, I'll let you know. Seriously though, y'all are life savers.

Cheers!

Alan
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Old 06-10-2008, 02:33 AM   #6
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Default RE: TIG vs Spot Welding and Tunnel Weld for 65 Floor Pans

Well after four hours of using a metal wheel to clean up the spots that are going to be welded not only can I not feel in my right hand, but I have one more question: When welding, do you guys recommend going from the inside or the outside? Our thought was that a seam on the interior would provide better structrual integrity and water drainage (if any water gets past the sealer we're going to throw on the bottom when we're done), but then again you guys are the experts so I'm sure there's something we haven't thought of.

Thanks.
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Old 06-10-2008, 05:40 AM   #7
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Default RE: TIG vs Spot Welding and Tunnel Weld for 65 Floor Pans

I think I'd rather put the seam on the bottom. Water, especially if it carried a little crud along with it, doesn't always flow out through tight openings very nicely. Tougher to weld without a rotisserie, though.


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Old 06-10-2008, 06:34 AM   #8
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Default RE: TIG vs Spot Welding and Tunnel Weld for 65 Floor Pans

Instead of using screws go buy a box of rivets use these about every 6" to 8" all around, except to the rocker of course. This will securely hold the entire pan in perfect place. Ensure that you have wire wheeled/ground clean all around! I went from the fresh cut up about 4 inches above where the new pan sets. Before placing the new pan in wipe it down well with a good cleaner to make sure there is no grease to mess up your welds. This simply makes for easier and less splatter while welding.

Also, from what I've read and was told you do not need to do any continuous welds on the floor pans. I paid 50 bucks (or was it 80.00.. regardless) on a hole punch that ran off our compressor. Punched a hole every 1 1/4" to 1 1/2" around the entire floor pan which took about 30 seconds. Drilling these is fine also though it'll take much longer. We then set the pan in place and started attaching it by drilling a hole through one of the new punched holes and popped in a rivet. Continue this all along the back, hump side and front as above.. every 6" to 8". Once this was done we started spot welding (or rosette weld) the pan to the rocker. Note that since the rocker is galvanized metal its a bit more difficult to spot to. Its good to have someone behind you with a long bar to apply some pressure anywhere its not tight.

After its all welded in I used a cutting disk (not a grinding disk) on the hand grinder to remove and smoothen out all the spots. Grinding them down takes forever and the cutting disk makes it fairly quick. Beware and alert at all times though. Hand grinders if not kept under control can do serious damage! You know how your hands feel after extended hours holding one lol.

Once welded and smoothed off make sure you have anything you need done regarding welding finished under the car. Then you can paint, POR-15 and seam seal all the edges. Between the seam sealer, POR-15, paint and undercoating it should never get water up in the overlap.

A few things..
[ol][*]Don't butt weld.. use an overlap and spot weld. I left about a 1 1/2" overlap (back, hump side and front toe board) with the pan on top. Attempting to butt weld so there is no seam IMO is simply too much work for a daily driver and will take you a long time to get fitted correctly.[*]Don't do continuous welds. Simply spot weld all around. There are very few places on a Mustang (or any car for that matter) that have continuous welds. The floors don't need them. It is also safer to spot so you don't distort the metal.[*]You will want to stagger the spots. Don't start at 1 corner and work forward (or back). Instead start at say the back corner and do your first spot then jump to the front corner for the second and then back and forth. This also helps from distorting metal.[*]When you come to a hole that has a rivet we simply welding through the center of the rivet and outwards like any other hole. The rivets we used were soft enough they just melted into the spot.[*]When I say spot weld I guess the "correct" term is actually rosette weld. For more info read FAQ #2 here.. and the rest is useful also.
[/ol]There are all kinds of ways to do floor pans. This is just how we did it. Others will of course have their own way. As long as it works, holds and looks good with carpets you'll be happy. Hope this helps.


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Old 06-10-2008, 06:40 AM   #9
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Default RE: TIG vs Spot Welding and Tunnel Weld for 65 Floor Pans

Since the edit isn't working....

btw we used a MIG welder for all our spot welding. As for seam sealer seams everyone does it a bit differently and it depends on what and how your treatign the inside and outside of the floors. I'd seal it from the bottom which is then going to be undercoated as well. If your going to POR-15 the inside of the car this will help cover and seal the inside as well as the primer and paint you'll be using inside also.
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Old 08-22-2008, 12:37 AM   #10
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Well good news. The floors are finally in! What a relief. Thanks for your help! Before doing all the finishing work I want to make sure I'm proceeding correctly. Is the following the proper order?

1. Brush seam seal top and bottom
2. POR-15 all new metal (top and bottom)
3. Prime all metal (top and bottom)
4. Paint all metal (top and bottom)
5. Undercoat bottom

A few questions: First, are all these steps necessary or are some redundant (do I need to paint over POR? Do I need POR? Do I need to prime over the POR? etc.). Second, is it necessary to use the two POR-made prep products POR recommends (Marine Clean & Metal Ready) before applying POR-15--Mustangsunlimited sells both so I have to think they're worth something? Third, do I need to strip the black coating that came with the new floor pans before seam sealing and/or applying POR? Fourth, how clean should the bottom of the car be before starting any of these steps (I have had to do some driving since installing the pans; I know I shouldn't have, please forgive me.) Lastly, how much of each of the products, if they're necessary, am I going to need (pint? quart?).

I'm getting really excited about how this is going to turn out. You guys are amazing. I couldn't do it without you.

Cheers!
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Old 08-22-2008, 06:44 AM   #11
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On clean metal, you will need to etch with something like phosphoric acid in order for the POR 15 to bond. Also if you plan to paint it, you need to spray some primer on when it just tacks up (feels sticky but does'nt stay on your finger), otherwise, after it cures, nothing likes to bond to it, and paint can flake off. I like using POR 15 but usually limit it to areas that are not seen like interior floor pans and in the door shell along the bottom (insted of seam seal) and had good results. On the bottom, a 2 part paint works great and will resist brake fluid. Remember that seam seal works two ways, it keeps water out, and it keeps water in. So be wise in its use. Heres a photo of butt and spot welds on a floorboard section that need replacment. The tranny tunnel was enlarged and the butts still need grinding. The rotisserie makes life easier.


Click the image to open in full size.
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Old 08-22-2008, 07:56 AM   #12
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Quote:
Originally Posted by CalStang65 View Post
Hopefully this is a quick question, but I'm getting used to the fact that they never are:

I've cut out the old floor pan on the passenger side and am preping the new pan for welding. Turns out the shop I'm working at only has can only do TIG welds. What are the pros and cons of tig welding where there were factory spot welds? I figure we can weld the entire frame rail to the floor, weld along the top of the connection to the rocker panel and elsewhere. A guy who knows more about welding thought that drilling out holes to simulate some of the spot welds for the rocker panel connection might be a good idea to avoid the two pieces working themselves apart . . . Another option (although I'd like to avoid it) is to TIG as much as possible and then pay a local welding shop to do the spots. Any thoughts you guys have will be really helpful.


Alan
Tig welding is a great option but vary expensive and time consuming. Those are the down sides, the ups, less heat distortion much stronger welds. the down sides are the reason most of us use a mig welder, some one mentioned using a cut off wheel to grind the welds down, good advice but i used a flap wheel, grinds and polishes at the same time last 4 times longer and cheaper in the long run and less dangerous.
good luck
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Old 08-22-2008, 08:31 AM   #13
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You know what I like about the forums....I can come here and read and learn a ton without even asking the question. :-)

A friend had told me to use rivets to hold in the floor pans but I was under the impression that butt welding was the way to go so I was trying to figure that out. Knowing overlap is ok helps everything make a lot more sense.

My only question is what do you use for seam sealer?

I am considering doing my floor pans soon so I have certainly printed out this thread for reference purposes.
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Old 08-22-2008, 05:27 PM   #14
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I used steel screws to pull the pan and frame rail together. Then I drilled holes in between the screws and did rossete welds in the holes. Then I welded the screws through to the Rails.
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Old 08-22-2008, 07:02 PM   #15
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I thought this was one of the most informational posts I have ever seen on floor welding so I messaged JamesW and asked if it could somehow be added to the FAQ. This is a post worth keeping around.
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Old 08-24-2008, 02:17 AM   #16
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Originally Posted by 67 evil eleanor View Post
On clean metal, you will need to etch with something like phosphoric acid in order for the POR 15 to bond. Also if you plan to paint it, you need to spray some primer on when it just tacks up (feels sticky but does'nt stay on your finger), otherwise, after it cures, nothing likes to bond to it, and paint can flake off. I like using POR 15 but usually limit it to areas that are not seen like interior floor pans and in the door shell along the bottom (insted of seam seal) and had good results. On the bottom, a 2 part paint works great and will resist brake fluid. Remember that seam seal works two ways, it keeps water out, and it keeps water in. So be wise in its use. Heres a photo of butt and spot welds on a floorboard section that need replacment. The tranny tunnel was enlarged and the butts still need grinding. The rotisserie makes life easier.
When you talking about etching before applying POR-15, should I be using the "Metal Ready" product put out by the same people that put out POR-15, or is that just a waste of money? How much POR-15 did you end up using? A quart? More? Less. I'm looking at two full floor plans plus seat risers (I'll probably do top and bottom just to be safe) so I'm trying to get an idea how much I should pick up without over buying. Thanks for any insight you can provide . . .
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Old 08-24-2008, 07:04 AM   #17
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That should do it. POR does'nt like to stick on clean shiney metal and the acid (metal prep) will etch giving it a better surface to bond to. For me, I would rather use the acid as to leave some rust. As long as it has phorsphoric acid, it should work, their brand or some off the shelve. I would think a quart would be enough. Also have some plastic wrap ready to put under the lid of the POR can when you re-seal it. If you get it in the seam and put the lid back on, you will not get it back off. If using the POR, I'm not sure what else, if any on the interior of the car that needs to be seam sealed. Their are a couple of places in the trunk and under the car that will need it though. I let it flow into the cracks and have had good results. Just make sure you check under the car after to see if any has leaked thru. Also wear gloves, if not, and you get this stuff on your hands, you will wear if for a week or so.
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Old 08-25-2008, 02:05 PM   #18
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Good call on the plastic wrap, I'm guessing that will save me a real headache. Now just so I'm clear: is there a need to paint on top of POR on the floor pans? Is it purely cosmetic? It sounds like a 2-part paint on the bottom of the car will help prevent crud buildup, but is this 2-part paint on top of a POR bottom coat or on its own? And does it change things that the floor pans I ordered are EDP coated? Do I etch on top of the EDP? Do I not need to POR on top of EDP? Or do I remove the EDP coat, etch, then POR?

Thanks again!
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Old 09-08-2008, 02:38 AM   #19
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So it sounds like I'm a complete idiot and won't be using POR b/c the new pans are rust free. I'm going to use a self-etching epoxy primer, then seam seal, then paint. I will then use an undercoating on the bottom. I figure that should work pretty well.

Any thoughts on how to patch up the hole shown below?

Click the image to open in full size.

I think that's the speedometer cable (I could be wrong), but that seems like an awfully easy way for water to kick up into the carpeting/car. Any thoughts on how to seal that up without screwing up the cable going through it? Is there a part that is missing?

Thanks again.

Cheers!

Progress update: Finished painting the interior-side of the doors and the rear quarter-panels. Put on the rearseat seatback upholstery, but it turns out I was sent the wrong seat-portion upholstery from the rear. It is literally 8 inches more narrow than the original. Be careful when ordering if you're trying to re-upholster.
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Old 09-08-2008, 07:58 AM   #20
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Sure looks like something is missing, your speedo cable should be much higher in the dash so i doubt that's it, i just checked my 68 and that hole is not there. i would find out exactly what that is and re rout it to its appropriate place and patch that mother up.
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Old 09-08-2008, 07:58 AM
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