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Pitfalls of flanged seams

Old thread, but I have a question?

If the problem with flanged seams welded is the expansion of the thicker seam metal will be different than the surrounding sheet metal, and cause ghosting, how come sheet metal with structural bracing welded on the back side is ok?

There has to be more to it.
Yes, as pointed out most sheet metal is attached around the perimeter so that any expansion from heat (sunshine) is not noticed. Put in a flange welded seam horizontally through the middle of a quarter panel and you have now changed the properties of how that same panel will react to expansion and contraction.
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Robert I watched a video where they flanged a piece of metal (small step) then showed how to use snips to cut away all but tabs made from the flange. The tabs positioned the patch but 98% of the seam was butt welded (everywhere but where the flanged tabs were). Is this an acceptable technique for not ghosting?
I'm not Robert but I am going to jump in with some thoughts. Under the right circumstances that might work but there are a lot of reasons you may have trouble with it. Robert can jump in when he catches up.

First, If your panels are under stress when you start the welding, you will never get it welded without it moving on you. If they are not under stress alligning a butt weld is no big deal.

Secondly, it is much more labor intensive to flange a joint, cut it off, leave the tabs, and weld it than it is to attach your panel with a few drill screws, scribe your cut line, cut it and butt weld it.

Thirdly. Your standard butt weld can easily be finished on both the front and back side making it a much nicer looking job.

If you feel you must. A small piece of scrap with a couple drill screws can hold the panels until you get it tacked. Then remove the drill screws and weld the little holes left and you are done without the tabs remaining. Personally, I usually use magnets to hold my panel until it is tacked. If the magnets won't hold it, I am probable going to be concerned about the fit anyway.. Just don't weld right beside your magnet.

The bottom line is, there is no purpose for reinventing the wheel. Any way you do it is going to be very difficult if you don't have solid, clean metal, fitted properly without being under stress, and the basic welding skill which you need anyway.

One other thing you need is lots of patience. plan your job well and enjoy the challenge. Metal working is addictive. The more you do, the better you get. The better you get, the more fun it is. The more fun it is, the more you do!

You get the point. Enjoy. :)))

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If the tabs are used simply to hold the panel in place, then once 98% of the seam is butt welded, I would suggest to cut away the tabs and butt weld the rest. We are attempting to reproduce the properties of the original panel, as stated above, that will expand when heated by sunlight without any visible indication of such. I would also add that not all videos you might see on YouTube show ideal methods. ANY flanging is not a preferred method, so perhaps another clamping method would help to get rid of the offset flange. Take a look at these Grippers designed for butt welding, an invention out of Ben's Metalshaping shop in Netherlands..


They make use of a small hole nearby the seam, which is easily filled afterwards, and unlike the butt weld clamps that spread the panels apart, these do not separate the panels as a means to effect the clamping.

Also, take a look at some of the videos by David Gardiner, a coach builder in UK. He trims the panel to fit, then using gas welding will tack the panel in place without any clamps at all. Just manipulating the seam together as he goes along with tacking the panel. He briefly shows this at 2:25 and 2:31 in this video....

His bodywork restoration DVD he sells is one of the best training resources, especially for someone using simple hand tools..
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Great posts guys! I have David Gardiner’s DVD. I’ve refer back to it often. I attempt to mimic what he teaches, and usually fail or have limited success, go back to the video and see where I went wrong, and give it another go. Between this forum and his dvd, I have been seeing steady improvement. Thanks to All!