How to Tighten up a Weld Seam on a Patch Panel.

No one’s perfect, but we can do our best to strive to get the closest we can get to perfection every day. These ideals are the same whether you’re a cook, a machinist, a landscaper, or a guy in his garage building an old car or motorcycle. One big lesson I’ve learned over the past few years has been to slow down and take the time to make sure that parts fit together as nice as possible before welding. Just blindly rough cutting a piece and trying to make it fit another piece is going to end with an uneven weld seam and won’t end well!


Ideally when you’re butt welding a panel with the TIG welder you want the gap to be as tight as possible without causing a buckle in the panel. There’s a few ways to achieve this but the easiest way for me has been to use a sharp scribe to scribe the cut line in a panel with the other panel laying over top of it. If I take my time with the Aviation snips I can usually cut right on my cut line. The key word is “usually”. Even when you take all the time in the world and are focused, something as dumb as a sneeze or as twist of a wrist can cause a cut to stray from the trim line and make an uneven gap on the weld seam.

For most they will suck it up and just fill the gap up with a bunch of weld (and heat). This means the panel gets warped more and there’s more weld to grind. I have done this more times than I’d like to admit and I’m sure there will be times in the future I will again, but there’s still hope to fix minor gaps in a weld seam without throwing away the part or filling it with weld.


We’ve been recently working on shooting a video on making a transmission and driveshaft tunnel for my Model A project (video and article coming soon!) and I had a perfect chance to show you guys how to adjust or tighten up a weld seam with a gap. While I was trimming this panel I was talking away and got a little off of my cut line in two spots and it required too much material removal on the belt sander to get it right. Rather than waste the part or time making another part, I just worked until I got it pretty close with a file and the sander and tacked the part on the ends and across the center of the seam.



With the part tack welded every few inches I could attack the unsightly gap. First get a dolly and hammer that matches the shape of what where you’re hammering and hold your dolly tightly behind the weld seam. Make sure the dolly is fully touching the seam and bridging the gap. You can then take your body hammer and strike it on-dolly relatively hard a few times.

By hammering on that area with the dolly tightly held from behind you’re trapping the metal between the hammer blows and the dolly smashing it a little with each hit; stretching the panel edges. What this does is push the edges out and closes up the gap. Depending on your gap you may only need to hit on it 2 or 3 times. Remember that thinner or softer materials like aluminum takes less force to stretch the edges. Check your gap after every 2-3 hits regardless as you can make the gap too tight and it may overlap or cause a high spot in the panel.



Here we can see the gap all tightened up and ready to weld. This tight gap across the weld seam allowed me to mostly fusion weld the seam and keep the heat and warpage down. In the end this meant less hammer and dolly work and sanding on the panel to get a nearly invisible weld seam.

With the flanges welded on I was able to sand the entire part to match and I have a part that looks as though it’s never been welded!

This technique should only be used for SMALL gaps. Don’t expect to close up 1/2″ gaps without warping or overstretching the panel and causing oil canning. If your gap is larger than about an 1/8″ you should take the time to use a file or belt sander to tune up the edges and get the fit a little better, some guys actually prefer that method!


Hopefully this little tip will help you in the future and save a lot of headaches and finish work!



  1. Do you recommend tig welding or mig welding for patching in areas when repairing rust damage?
    Appreciate your site and products. Please keep your prices reasonable and competitive.

  2. Great for people with Tig’s how about for more common d.i.y. er’s who use a Mig?

  3. I am making a transmission tunnel similar to the one shown in the video. I have trouble making round shapes that decrease in radius over their length as this tunnel does. Is there a video that I could view or purchase that demonstrates how this was made?

  4. I have had one of your tig welders for about 6or7 years . I have never used It . I bought the welder and plasma cuter at Christmas time as a package . the welder for me . the tig for my brother in law . the tig welder I don’t know how to use it do you have a vido .

  5. I own a 29 model A truck. I wish I had the equiptment to do the things you do and make it look so easy.

  6. Thank you for this! I am replacing the floor panels and trans tunnel in a Jeep, and this was very helpful to me to read these tips. It’s always good to be able to learn from someone with experience when doing these projects for the first time.

  7. I would like to know how you can do this on a blind area such as a truck bed side when there is no way to get anything behind the weld seam.

  8. Well done; I have a great respect for those who have the talent and patience to do this kind of work. Fortunately, I have three sons who excel in fabricating and are quick to bail me out when I get into these problems.
    BUT – I always look forward to every tip in hint I can find. Looking forward to more!

  9. I have often cut access panels to get inside of the hidden area. It all depends on how far you want to go to get the panel completely straight after welding.

  10. Hi Daryl, stay tuned to our Tech Tuesday emails or subscribe to our Youtube channel, we’re finishing up filming and editing a how-to video on the transmission and driveshaft tunnel I made from scratch where we show just that!

  11. Tightening up the weld seam is the same process regardless of what welder you’re using. You just can’t effectively hammer and dolly a MIG weld seam like TIG or Oxy-Acetylene welds.

  12. Richard, TIG welding is my favorite and the cleanest way to do it, but it does take a LOT of practice to get yourself skilled enough to TIG weld sheet metal. MIG is quicker and easier to learn, but harder to get as nice of a finished product.

  13. Thanks for the info. That’s a great idea on tightening up the weld seam. I’ve used my mig and fill and grind. I had one pop on my ’50 chevy quarter panel. Pain …

  14. Just purchased a Tig200 AC/DC. Please clear up a question for me. Using the foot pedal and the setting on the pedal is set to say, 125 amps .Is the max current you can get with this setting with full pedal depression 125 amps? If the answer is 200 amps, how do you know when the foot pedal is at the 125 amp setting. I have been hearing conflicting answers to this question.

  15. Hi, the setting on the pedal is your max amperage. If you put the pedal at 50 amps you will only get a max of 50 Amps with it fully depressed. Hope that helps! Our tech team can also answer product questions like this at:

Leave a Reply

Back to top button