During the frame off restoration of Project Dangerboat (the 1972 Oldsmobile Cutlass Supreme), it was noticed that the front floor pans had some pinholes that would need to be addressed. While refreshing the interior and the interior was removed, it was the right time to address this.

Floor Pans

Let’s just say this, I’ve wanted to get into welding for a while, so this is my excuse. Most welders will recommend Mig welding for thin sheet metal work as the automatic wire feed and instant tach weld without needed to add rod help limit heat and burnthrough, however I want to learn TIG welding for other reasons, so I purchased a decent TIG welding setup and got to work.

If enough people care about the specifics of this process, comment below and I’ll write a more detailed post on techniques etc.

General concepts:

• For Thin sheet metal, the gaps need to be as small as possible between the new and old metal. Preferably 0 gap, but no more than 1/16″.
• Rusty metal is almost impossible to weld efficiently. The welder will burn holes through the thin metal and you’ll turn what seems like a pinhole into an area the size of a quarter in less than 1 second. Don’t try to weld up an area with a bunch of pinholes because the surrounding metal is likely very thin. If you only have a couple pinholes, and you’re sure the metal is good in surrounding areas, you may be ok. You’ve been warned.
• To Butt weld or to Lap weld: Butt weld is regarded as the higher quality method, but more difficult to execute in both cutting precision and welding thin metal. It results in a cleaner look, but not if you burn through a bunch of area’s trying to execute it. Lap welding can leave areas that trap water/corrosion. Don’t lap weld in corrosive or salty environments, but with proper sealing it really shouldn’t matter either way. Recall that the manufacturer used lap welds all over the vehicle. I butt welded my panels, and it was challenging.
• A magnetic copper backing plate or heat sync helps weld gaps or thin areas alot by absorbing heat and providing a flat surface for the weld to lay against. Carbon steel TIG/MIG rod won’t stick to the copper. They are only ~30 bucks, just do it. Panel clamps to hold the panel in place are also helpful, and about 9$ at Harbor Freight etc.
• Be careful to keep heat low. Work in small areas at a time, and move around the panel to distribute heat. Heat is less important to cosmetics on something like a floor pan versus a fender, unless your car is intended to be show-room perfect.

Tools:

• Angle grinder with thin and thick cutoff wheels. The thick grinding wheel will be used to grind down welds, the thin wheel will be used to cut out panels and sections.
• 60 or 80 grit sanding disc for the angle grinder
• metal cutting sheers (electric) make cutting straight line areas ALOT easier and cleaner, but they are not useful for bent areas or turns.
• Dremel tool with cutoff wheel for tight areas
• Welder with all necessary accessories
• thin metal needs thin wire/rod and thin tungsten if TIG welding. I used 1/16″ for most work and 3/32″ rod for areas where my gap was too large, or I burned through.
• Wire brushes
• Hammer and dolly for dents and panel adjustments.

Welding:

• Disclaimer: I am NOT an experienced welder!
• DC welding
• 30-35 amps seemed to work well in most cases for my TIG welder and metal. Above 40 burned through even healthy floor pan areas.
• 1/16″ tungsten and rod.
• 100% Argon purge (for TIG)
• #4 or #5 cup, any smaller size should be OK
• I highly recommend a modern electronic self-dimming mask, since you’ll be working in low light areas like under the dashboard.
• Tip: Start the arc on the donor metal rod and then move the melt puddle onto the panel gap to be welded. This is a thin metal technique that greatly helps limit burn through.

Steps:

1. Purchase your new floor pans
2. Decide where you will stop trimming and mark/trace
   1. Make sure you look at what is behind the panel before deciding. Don’t cut through your fuel lines, oxygen sensor, exhaust, wiring, brake lines etc without realizing they are there. Keep the heat from welding in mind as well.
3. I used two different approaches on the next steps. I found the B method worked better, mostly because cutting and marking was easier on the new pan while it wasn’t in the vehicle, so I ended up with better cuts.
   1. cut out the rusty areas of your original pans, and trace them on the new pans. Then cut the new pans following the OUTSIDE of your trace lines on the new pans. Remember, it’s easier to trim again then it is to weld new metal in if you leave gaps.
   2. Using measurements, mark areas on your NEW pans and cut out your new pan. Then place the new pan inside the vehicle over the old pan and trace it. Now cut out the old rust metal pan following the INSIDE of your trace line.
4. Begin test fitting your new pan into the hole. This will take more time than anything else, and require multiple small trims and re-tries.A hammer and dolly will likely be needed in this step to address dents and bends from the shipping and cutting process. The more time you spend here, the easier welding will be.
5. Once content, use your panel clamps to hold in the new panel.
6. Tach weld the new panel in place, at least 1 tach on each side.
7. Weld. This took me about 2 hours to get all the way around.
8. Grind down your welds using the thick grinding wheel and sanding disc.
9. Check for holes in your weld using a light on the oppose side.
10. Re-weld as needed.
11. DONE!

Finished Welding

This was admittedly challenging, especially for a new welder, but once I got started the process began to move more smoothly. Take your time and be patient. Regarding welding, practice makes a HUGE difference, so find some thin scrap metal and practice butt welding before putting the torch to the car (although I admit I didn’t practice, at all).

Painting:

Eastwood Rust Encapsulator was used.

Sound Deadening:

LEFTLANEBRAIN