But welding sheet metal

**Ron66** · 09-07-2013, 01:44 AM

I've been working on a sheetmetal project where I'm making my hood into a cowl hood. This means I have to add some thin strips of metal to the existing hood. I cut and sanded the first part so it had zero gap when I butted it up to the edge of the hood. Then I started tacking it with the tig. By the third tack the metal started pull so badly that it overlapped. Next piece I put in I will add some shim stock spacers about 10thousands thick then the tacks should pull it tight. Anybody else experience this?

**Rambozo** · 09-07-2013, 01:56 AM

Yes, with any metal, but more pronounced with sheet metal, heating and metal shrinkage is something you have to work with as you fit pieces. It takes practice and skill to pull it off. I can't say I'm that good at it, but those that do autobody sure need to be. Generally you have two pieces that have a thin pie gap that closes up as the two parts are tacked together. There are different techniques to control shrinkage during welding. Some take shrinkage into account when making the parts, others go for the death by a million tacks and try to hold everything in place before welding. Skip stitch and or back step welding can help, too. Careful shrinking and stretching after the weld can take care of minor distortions. You can find all kinda of hot rod pros on YouTube that do crazy sheet metal manipulations, and all without any body filler!

**Jason** · 09-07-2013, 02:55 AM

When I am welding in sheet metal I try to fit the piece close to where it is going to go and then just work it into place with a body hammer as I tack around the edge. Once I get tacks all around the piece, I will place a couple tacks together and just move around the piece trying to control the heat to avoid warping it.

**its_34** · 09-07-2013, 04:04 AM

Originally Posted by Rambozo

?... You can find all kinda of hot rod pros on YouTube that do crazy sheet metal manipulations, and all without any body filler!

Those guys are the real master-crafters. I remember being horribly disappointed years ago when a certain custom bike show came on TV. A lot of the metal work was roughly mig'd together and the paint & body guys did all of the beauty work with filler and lots of sanding.

**Ron66** · 09-08-2013, 01:32 AM

I'm getting pretty good with the body dolly wet but I may need to buy a metal shrinking hammer/dolly. Finished welding the first seam of 6 pieces today. I'm going to grind it smooth, do some dolly work and see how much better I need to be on the next seam.

**youngnstudly** · 09-08-2013, 07:11 AM

I am getting better at tig welding sheet metal, but I have had a bit of practice from welding sheet metal in my trade for starters. The bigger sections of thin sheet are what I have trouble with still. I really get a kick out of watching my dad gas weld sheet metal when doing rust repairs on cars. Of course he's been doing it since the 1960's, and is more comfortable gas welding and using the torch to shrink metal than welding with any other process, since it comes more natural for him. MIG was just something that he had to learn for his trade in later years in order to keep up with technology, and he's good at it, but still better with oxy/acetylene. I think he will do good once I teach him the basics of tig welding. His main issue now is poor eyesight.

In the sheet metal trade I got used to welding and metal finishing everything nicely since it's usually exposed stainless (indoors), galvanized (outdoors/rooftops), or copper (outdoors). Especially the food service type items. No bondo allowed (haha). I always make sure to put the smallest tacks possible (get in and get out ASAP to minimize heat input), use as many vise grip clamps as I can (or use cleco's), and use a backing of some nature (usually copper) when possible. Fit up is everything. And of course, the tungsten needs to be sharp, and the filler rod needs to be small (diameter). The end result is what's important, and everyone does things a little different. You just have to figure out what works for you.

**Ron66** · 09-08-2013, 11:41 PM

Put in my second piece today. Left a small gap and let the weld close it. It worked much better. I also put a lot more tacks and use compressed air to cool the panel after every 1/2" of weld. This project is going to take a lot longer than I thought!