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.
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 centre 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 aluminium 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!