Repairing tunnel « My Beetle Restoration

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Welding the Tunnel Bottom Plate

by Garage Weasel on Apr.30, 2024, under Chassis

I'm finally at the point that I can weld the tunnel bottom plate back on. First, I touched up the protective coating on the inside of the tunnel with Eastwood Matte Black Rust Encapsulator. Then, I cleaned up the areas where it will be welded.

Next, I masked off all areas where the panels will fit together and sprayed them with U-POL Weld #2 Copper Weld Through Primer.

It's been a while since I last welded and I had to buy a new welder, so I really didn't know how this was going to turn out. I started by welding the welds on either side of where I had placed the sheet metal screws. There was a steep learning curve to overcome. The holes that were created with the spot weld cutter were huge (3/8"), and many were very close to the edge of the plate. Getting the welds hot enough to penetrate the 2-milimeter plate and fill the holes without melting away the thin outer edge was very difficult. Fortunately, the replacement rails were quite a bit wider so if the welds did melt the outer edge away and spill over, it shouldn't really cause an issue as the rails will be trimmed back when I fit the floor pans. Out of curiosity, I counted the welds on each side - 63 on the driver side and 76 on the passenger side. I took my time and made sure that I didn't get the metal get very hot. After doing all of the spot welds, I ran a straight bead on the rear seam where I had cut the bottom plate. I received mixed results, but I did get it done. Lots of grinding ahead!

I flipped the chassis over to check the penetration of the welds. I was pleasantly surprised how well they had penetrated. I wasn't able to get this level of penetration with my last welder despite the settings.

Grinding down the welds took hours, but the welds were solid throughout and I only had to do a few touch-ups. I was able to get it fairly flat and even and felt good about it after it was done. After years of not getting anything done on this car, this felt like a big step in progress.

I used a Scotch-Brite™ Clean and Strip XT Pro Disc to remove any remaining paint, rust, undercoating, and mill scale on the bottom plate. These discs do an excellent job and remove very little metal. They are by far the best thing for removing mill scale.

I then sprayed primer over the bottom plate to keep it protected until I get to the paint prep stage. Quite a change from the rust-eaten tunnel I started with!