"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….

i always but the 2 pieces together. i usually make a spot weld every inch or so. {very small and quick} letting the part completely cool. then i repeat the process until its welded completely. it takes some time but i have very little problem with worpage.

i did some 57 chevy fenders about 2 years ago that someone overlapped the panels. this made a big mess the bottom of the fender was hanging out past the door and rocker panel. and if you got it to line up at the bottom the top was way off. so i cut the old patches off and installed new ones that were but welded and the fenders fit much better.

that overlapping stuff is the lazy way out in my opinion you get a much better job with a butt weld. and like i said if you go slow the amount of warppage will be minimal.


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My 68 (http://www.chevelles.com/showroom/68racer1.jpg)
My Engine (http://www.chevelles.com/showroom/68racer2.jpg)

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.

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...Eric

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