About those Patch Panels, Opinions please

[Terry, NJ]

About two years ago I was invited to an open house of a local high end restorer. (Not a mod A in sight) I was talking (picking brains) of their top body men and how they do patches. we were looking at a, maybe 4" circular patch and I noticed all their patches had no sharp corners. His answer was that round corners pull less than straight corners when welded in. Since there's a couple of threads on here about welding and patch panels, I thought I would throw it out on the table for whatever.
Terry

[wrndln]

I have heard what you heard form the restoration fellow about no square or sharp corners on patch panels. I am not really convinced that it makes a big difference. I think the key thing is not to weld too much at one time getting the panel so hot is starts to warp. In theory "no square corners" seems like a good Idea. Many times not having square corners is difficult to accomplish.
Rusty Nelson

[chopo]

ive done many many this way with no issues

[BRENT in 10-uh-C]

I think it matters only if the panel is not correctly installed. Round corners or square corners matters not if the panel is properly fuse-welded into place. Complete & total penetration between both panels followed by hammering to planish the weld will be as strong as any.

.

[bart78]

I do it because its less welding.

[chopo]

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of course butt welds only

[Tinbasher]

Actually it is done to reduce the warpage in the panel. By rounding the corners the heat travels around the corner instead of piling it up in the corner which cause more expansion of the metal and then more warpage. Level 1 apprenticeship stuff.
Everything to control the heat helps. Better fit, small welds, weld placement, rounding the corners, tipping the edges 10 degs. It all helps. Give it a try on a piece of 18 gauge sheet metal. Round one corner and heat it, leave one corner square and heat it and see what happens. 10 to 1 the squared corner will lift more than the rounded one.

Have fun. The Old Tinbasher

[Kevin in NJ]

In all my digging on the subject of doing patch panels I never ran across the rounded corners idea.

I am trying to get my hand around what tinbasher is a saying, but my intuition/ experience is telling me something else.

I know when working a panel in place with a tig and a tightly matched butt weld I have no problems. I have done mostly square corner stuff with some round and some angled. They all came out fine.

The key is to not think about how much I have reduced the shrinkage. It not about how much you have, it is all about how well you correct what you will have. So what the metal distorts because the metal has shrunk. A little or a lot who cares, the fix is the same. Hammer on dolly till the panel is back to the correct shape. I do this continuously. I do my tacks planishing as I go. I do may zillion spot and very short runs and planish as I go. I get done with all the welding and finish my planishing and lightly file.

Best I can tell people worry too much about the wrong things with this metal working. Do your welds nice, level welds if mig, planish- repeat. You should not be thinking well I did it this way and I must not have any shrink. You weld then you correct for the shrink (if you can).

It works much easier then I had ever imagined once I learned the correct information.

Round or square, make the panel shape correct. Make a nice and tight fitting patch trimmed to fit the hole. Then weld it in.

It is all in having some experience and some knowledge on the correct techniques. If I can manage to get my hands to do the job it really can not be that hard to do. I am very impatient.

[chopo]

mostly its all about control

[Roadster62]

You drill a hole at the end of a crack, to end it before welding. Maybe the rounded corner is better than a sharp square corner.

[Terry, NJ]

T.B., This shop I was in was a high end restoration shop (Pre WW1 stuff, Cads, Rolls, a nazi era Mercedes, Terra plane, a Gull wing Merc. (1955?) Not a model A in the bunch. They had a few Aluminum bodied sports cars, one had been in a devastating wreck and they formed a new front end clip (You can't buy this stuff) for it. In short, they were crackerjacks and knew their stuff. When skill of this magnitude speaks, I listen! I don't claim even apprentice 101 in the way of skills. I read these threads and try to discern what Brent, Tom, H Chauvin, Kevin and others whose names escape me. And It's all good! But I'm floundering again, due to a lack of knowledge. This is my first Mod. A. I appreciate everyone who takes the time to answer. Your explanation makes sense. While I rarely ever welded 16 or 18 ga., It was usually 1/4" or more, I am well aware of the heat "Gathering" or accumulating in front of the rod. I wanted to sit down with a engineer and design a "Black box" that would be incorporated into a welding machine (MMA) to cut the heat back as a weld progressed. Never did! always something else! But I was well aware of the increase of the heat as the weld progressed. And the effect that increased heat would have on the pulling of the metal.
Terry

Originally Posted by Tinbasher

Actually it is done to reduce the warpage in the panel. By rounding the corners the heat travels around the corner instead of piling it up in the corner which cause more expansion of the metal and then more warpage. Level 1 apprenticeship stuff.
Everything to control the heat helps. Better fit, small welds, weld placement, rounding the corners, tipping the edges 10 degs. It all helps. Give it a try on a piece of 18 gauge sheet metal. Round one corner and heat it, leave one corner square and heat it and see what happens. 10 to 1 the squared corner will lift more than the rounded one.

Have fun. The Old Tinbasher