"Find an instructor that does more metal finishing then filling, and but welds panels completely, not tacked and lapped."

I copied the above from a different topic although It got me thinking about just how to do it. I am a student and my instructor has told us to use a lap weld when putting in panels. For example, the lower right front fender of a '68 Chevelle had rust on just at the bottom and I was instructed to cut it out, leave about 1" of overlap from the purchased replacement panel with the new panel shoved under the good existing panel to form a lap. Before welding, drill and screw in screws to pull the two panels tight and then weld in about 1" from side to side until completely welded. The same instructor told us that doing this as a butt weld would warp the two panels even if done slowly and in different places (not one straight line).

Any advice to a student??? I'm confused. I want to learn how to do good work.

Thank you for your thoughts-

Dan Latta

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1970 El Camino
Student, Santa Monica College
http://photos.groups.yahoo.com/group/ElCaminosandChevelles/lst
Santa Monica, CA
Current ground up restoration in progress: All parts brand new except rear end: GM 350 crate motor w/ Weiand dual plane intake & Holley 600 cfm carb, K&N exhaust. Doug Thorley Headers w/ Flowmaster pipe & exhaust. Rebuilt transmission from A1 w/ shift kit & 2500 stall converter, Hurst pro-matic II shifter, 15" Powder Coated Rally's , Chevelle SS steering wheel, combo oil/tranny cooler, ARP bolts everywhere.

Project almost done-at this point-wish I had the resources and space to do a frame off. Anyone take the frame off before in a standard size garage? Now that all the new parts are in except radiator, it wouldn't be all that to tear down again. Hmm….

Check out the link in my sig. It has some pics of a quarter skin I buttwelded on my 70.You can use the same technique for smaller patches also.


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http://photos.yahoo.com/ochrisl

On Crank and Chrome, speed vision, they just did a segment on this. The way the body man did it was to cut out the affected patch,- make a panel that covered the the spot with about a 1/2" overlap,- tack welded the corners, -welded all away around the patch,-hammer recessed the patch,-used plastic bondo over the top of that. I think you can go to there web site and find this segment. Hope this helps...........bk

Thats not butt welding.Moisture will develop in between the panels and will cause the filler to lift and bubble over time, BTDT.

Just finished quarters on my 69 conv. I was told by just about everyone to butt weld because moisture weld gather in between laps and rust no matter what you do and the butt weld appears much nicer on the inside (of the trunk and can easily be finished off.

Lap welding can produce the same amount of warpage that a butt weld will. Its not the type of weld being done but how you do it and the amount of heat introduced into the metal. Lap welds have there place in the automotive repair but not on the lower corner of the fender. That lap weld will leave a exposed joint on the backside allowing moisture to sit on top of it and rust will begin. Rust always comes back at a welded joint because of the disimiliar metals welded together. But with a butt weld no joint is present and water cant collect on it and start to rust, also you can get the weld covered with paint where on the lap weld you cant.
On a butt weld you dont want the panels butted together you want a small gap, just big enough gap that the wire from your mig welder will fit through. I use size .023 wire nothing smaller nothing bigger. Use too big of a wire and extra heat is added into the panel because you need extra amps to melt that bigger sized wire into the weld pool.

Always tack weld the entire panel dont just start welding, if you do the two panles will pull apart. Leave a about a inch gap between tacks and jump around on the panel when tacking just dont start at one end then go to the other. Start on the ends then put one or two in the middle, now you can start to jump around. Once the tacks are done fully weld the pieces together only weld very small amounts at a time like 1/4 inch. Then move to a different spot and weld 1/4 inch. Let the panel cool and begin again. Some people like to blow compressed air or use a damp rag to cool the welds but I dont care too. I think that using those methods shocks the metal and work harderns it and creates more warpage then just allowing the weld to cool on its own.

One neat little trick that you can use while butt welding if your gap is too big is to place a flat piece of copper behind the gap. The weld willnt stick to copper and adsorb some of the heat also, just something to remember if you find your gap too big.

Its true that a butt weld is much harder to do but the added benifts you get by doing it outweigh the extra effort. Butt weld the patch panel and you will be happier knowing that you made the best repair that will last not the easy one that will come back in a few years. Dan if you were to tour any custom or resto body shop the butt weld is the weld of choice. Just look through mags like street rodder or rods and custom, every weld Ive ever seen in those mags is a butt weld. It didnt matter if it was welding together a chopped top or rust repair patches the butt weld was used for its lasting finish...Eric

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http://briefcase.yahoo.com/bc/sevt_chevelles

[This message has been edited by sevt_chevelle (edited 04-07-2002).]

Thank you, thank you. I had a feeling that a but weld was more appropriate although harder to accomplish in that area given that there holes to line up along the inner fender well.

Next part of the project is the portion just below the rear window ('68 El Camino) where water has leaked and created rust. Instructor wants to cut out the bad part, which runs the entire length of the window, size the pre-fabricated patch panel over the area (lap) and make permanent with a combination of drilling screws from the outside of the car in to pull the patch tight against what remains of the metal below the rear window. Install several of these screws and remove 1 by 1 and replace them with MIG plug welds. On the interior side, use a series of tack welds to further seal the patch.

I guess a good question here is does anyone have experience with this repair of the rear "rain gutter" of an El Camino. Pictures would be great! My '70 has a similar problem as the '68 does in the shop.

I have a picture of mine along with pictures of the lower fender panel repair that I did when I didn't know hardly a thing about this type of repair. Look in the "Before Album"
http://photos.groups.yahoo.com/group/ElCaminosandChevelles/lst

Thank you again for sharing your expertise and experience!

Dan Latta

I'm the one you quoted. I hate it when people tack and lap patch panels. I hate to say this, but your instructor is not that good. There's no way you can metal finish a patch panel that is lapped!

A lot of people are too concerned about warping panels when welding. Yes, you should do small areas and yes you should try to avoid warpage. One important thing to remember is that if there is warpage, then do not try to fix the problem in any area other than that of the weld. When you weld, there is an area that is called the heat affected zone. This is where all of the distortion takes place. Sometimes, it can cause a problem far away from the welded area. Do not be tempted to work the area in the middle of the panel. What causes these types of problems is that welds shrink as they cool. If you cool a weld too fast, you will cause the area to pull even tighter. To correct a situation like this you need to use a hammer and dolly to stretch the shrunken metal in the heat affected zone back to where it should be.

Look at how you shrink metal with a torch. You heat a small area cherry red, hammer it back down and quench with a wet rag. The quenching shrinks the panel even more.

The above shrinking technique is happening when you weld, just not anywhere near as fast or as much.

You do not HAVE to use a MIG welder for this type of repair. Many people that build car bodies by hand for a living use a small oxy/acetalene torch to perform this operation. In this case, you would need a very tight fitting joint. The idea with this is to not use any filler rod except when you are about to blow a hole in the metal and at the ends. This process is slower than the MIG process in the welding stage, but requires less finishing work after the weld. With a MIG weld, you have a lot of grinding to do.

You don't have to have the latest greatest to do this kind of work. The Italians beat Ferarri bodies on tree stumps with mallets and gas welded them together.

Butt welding is the way to go for your type of repair.

"In this case, you would need a very tight fitting joint. The idea with this is to not use any filler rod except when you are about to blow a hole in the metal and at the ends."

dselko: interesting, I would think that there wouldn't be enough penetration with oxyacetylene for a solid fix especially without rod. From a finish point, it definitely sounds like it would provide a very clean weld with minimal slag to grind off(better for less warpage and later less filler). I guess it definitely depends on the bead you're able to control.
At school we use a 201 tip for oxyacetylene welding-is there a smaller setup? There is the 200 tip for brazing. Other than that, I don't know what is available for oxyacetylene.

One thing too that I just discovered is the use of welding magnets to hold two pieces of metal together for a buttweld. I was having a heck of time using the vice clamps to hold metal together for a weld. Those magnets are great for keeping the appropriate gap in order to make the initial tack.

One thing is for sure-it makes a whole lot of sense to do a butt-weld. It allows you to adequately protect the inside piece with sealant as well as use less filler on the outer surface. Awesome. Thank you!

Dan Latta

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1970 El Camino
Student, Santa Monica College
Santa Monica, CA
ACES #5204
SCCC #416
Watch the "progress" at:
http://photos.groups.yahoo.com/group/ElCaminosandChevelles/lst

Penetration is definetly not a problem. If your joint is tight, you will lose only about 2 thousands of thickness which is not too much on 20, 19 or 18 gauge. I took at metalshaping class at Ron Fourniers shop in Troy, MI. He was pushing gas welding sheet metal, both aluminum and steel. We used a special torch called a Henrob. It uses very low gas pressure so it won't blow a hole in hot metal. Any small torch will work. I have the Henrob and a very small unit called a MECO Midget. The Midget is a real featherweight.

Many of the high end metalshapers like the TIG units as well especially for aluminum. When you gas weld aluminum, you need to use a highly corrosive flux which if not carefully cleaned will cause paint to fail later.

Almost none of the high end guys use MIG. I am not talking about body shops. I am talking about people who make an entire car body from scratch and use NO FILLER at all, not even on the weld joints.

The main reason MIG has taken off in body shops is speed. These things are much faster than gas welding or TIG welding. Almost anyone can make a good enough weld with a MIG, so training is not as much of an issue. A body shop would go out of business if they tried to gas weld for collision repairs. Also most restorers could not afford to have their cars repaired this way. Also the HSS (High Strength Steel) used in most modern cars should only be MIG according to most of the manufacturers.

This process is slow and requires a great deal of practice.

David

If the panel gets warped, grind the weld flush and hammer on dolly back and forth on the weld itself. The warpage is created because weld shrinks the metal. By on dolling the weld, you stretch the shrunk area.

Assuming your mig welding, Cooling the weld faster with an air nozzle will reduce the warpage. It prevents the heat ring from expanding further out.

For patch panels toss the brazing rod away. Paint will not stick to it. You'll have to burry it under filler.

[This message has been edited by AlMyPal39 (edited 04-08-2002).]

I have a somewhat related question. I recently discovered my Lemans has had a quarter-panel replacement done way in the past. It was lapped and brazed every inch or so to join it to the body (the replacement quarter was sectioned and joined around the sail panel area, not near the roof like a factory installation). I originally wanted to have the braze ground out and MIG the entire seam, but I was wondering if I could carefully cut down the middle of the lap with a cutoff wheel, creating a small gap, and then butt weld the two panels together. Would this work? Sounds like a better way to go.
I can post a pic of the damage, I know I haven't done a good job explaining it.

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Tony Nausieda
1970 SS 396-4??hp
1977 Caprice, no dingle balls or hydraulics
1966 Buick GS 4-sp vert FOR SALE
1965 Le Mans EFI'd 468, 4-sp
1639 total cubic inches :)

70L34,

That idea works. If your talking about the area where the quarter meet the roof, then that area is usually lapped and spot welded from the factory and then covered with lead. In this case, would do what the factory did. Assuming it is a full quarter panel. If it's a skin, then cut and weld the panel completely.

I wish they had done it factory-style along the sail panel.
Picture this: the original quarter was cut off the car and they left about a 1-inch border around the base of the sail panel. This section was removed from a GM replacement quarter panel, and the replacement was brazed everywhere, including this lap around the base of the sail panel. I will post a pic, this is confusing even me. http://www.chevelles.com/forum/smile.gif

I just think a butt weld is the way to go for the long run. Planning on keeping the car a while.

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Tony Nausieda
1970 SS 396-4??hp
1977 Caprice, roller SB406 (soon)
1966 Buick GS 4-sp vert SOLD!!
1965 Le Mans EFI'd 468, 4-sp
1639 total cubic inches :)

dselko

You sound like a body man, are you? If you are I need some work done on my 71, the lower rear of each quater and a little in the right rear window, interested? I live in southern Maryland.


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www.muncie4speed.com (http://www.muncie4speed.com)
Gold 67
1967 Malibu, 2nd owner.
1971 Malibu, been in the family since new.
There is nothing like rowing through the gears at 7500. Stick cars are so much fun they should be a controlled substance!

I am not a bodyman. I am just interested in metalshaping/body work. I bought a rust bucket 69 SS that needed quarters, fenders, trunk floor, etc. My main purpose for purchasing one of these rather than a completed car was to learn how to do this stuff but no ruin a very valuable car. I can hardly find time to finish my own car. I wish of knew of a good body shop to recommend in your area. Anyone know of a quality body shop in southern MD?

David Selko

I was about to go out to the garage tonight to do a little more work on my fender patch panel (fitting so far, haven't welded it in yet), but I'm so glad I came across this topic first! That photo series on the quarter panel was very interesting. I'll be doing the same job in the near future. Thanks for everyone's input on this subject, this is what makes this such a great site.
Rich

From another beginner, I just want to say "thanks" for all the good info in this forum and for posts like this!

I have a question on the butt-welding tho... what is the 'proper' gap to have between the panels as you start to weld them? Does it matter how thick the sheetmetal is? I will be doing MIG gas welding and using the .023 wire.

Thanks,
Bill C.


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Bill C.
'71 SS (now with 467BBC)
'70 Nova 350/700r4
ACES #2780
Colo Spgs, CO

BC

The best way is to butt them together. Someone's gonna disagree with me, or suggest Eastwood clamp that space the panel. If you have a small gap, you are more likely to burn through because there is no place to dissipate the heat.

I use .023 wire and use that for my spacing of the gap. But proper spacing for a butt weld should be the thickness of one piece. This helps weld penteration and problems with expansion and contraction. You want and need a gap between the metal cause when you weld the two together that area around the weld shrinks, and if you have no gap the metal has no where to go and there for forms a bulge or a high spot.

No gap works best, Penetration with sheet metal is no problem. It's how you weld that is important. If gaps works for you then fine. We've had no problems butting then together. I can actually have better welds butted together then most professional bodyman can weld with a gap. It's all in the technique. What ever works for you is important.