One of the biggest headaches in automotive restoration is properly removing the old panels that need to be replaced. Recently, I was confronted with a project that could easily have required a Tylenol or two – despite my years of restoration experience.
I had a 1967 Firebird in really bad shape. I estimated that about 90 percent of the sheet metal had to be replaced, including both quarter panels, the roof, trunk floor, main floor, outer wheel houses, taillight panel and more.
The proper and best way to remove old panels is to rough cut a section and then cut away the top layer of the spot welds, leaving a clean, undamaged surface to attach the new panel to. Typically, there are several ways to do this. You can use air shears, nibblers or cutoff wheels. Or, you can take the approach that I employed: using a plasma cutter.
For me, the Hypertherm Powermax45 XP is essential for the numerous panel replacement jobs I’m given. Not only is it easy to set up and use, all I need is a 220-V outlet and a compressed air supply. Even if I didn’t already have an air compressor in my garage, Hypertherm offers the Powermax30 Air, which I’ve also used and am very impressed with. The cord for the torch is 20 ft. long, plenty enough to reach most work areas in an average-sized garage.
Using the Powermax45 XP on this project drastically reduced the amount of time it took me to remove the old panels. But, perhaps even more important, it also virtually eliminated any chance for even the slightest headache.
Even though the project required nearly all of the sheet metal to be replaced, this article is going to focus on the trunk floor. For trunk replacement, it’s essential to keep the frame rails intact. The easiest way to do that is to create a guide on the top surface by getting under the car and plasma piercing or drilling a series of holes around the frame rails, leaving 1/4 in. to 1/2 in. between the hole and the edge of the rail.
Before starting to cut, however, it’s important to carefully assess the panels that will be replaced. For example, when removing the quarter panel, take careful note of the B pillar and draw a line around it. Know what you are cutting into. Sometimes the inner framework of the car is just under the surface of the part you are cutting. Carefully plan your cutting and be sure to check the seams and remove any old seam sealer.
As far as rough-cut edges are concerned, that is one of the outdated myths about cutting with plasma.Older units had torches that simply could not do what the new technology torches can do.
In the case of the Powermax45 XP, it has Smart Sense technology that automatically adjusts gas pressure and flow for optimal performance. It produces clean, sharply cut edges similar to what you’d expect from a bandsaw. Older units were able to cut 3/8 in. whereas the Powermax45 XP is rated to cut cleanly through 5/8 in. It’s even powerful enough to cut through 1 1/8-in. material if you occasionally need it to, though the cut will be rough. The equipment can also be set at 10 amps, which makes it easy to create precise cuts when dealing with thin metal or “carving” away welds.
An additional feature of the Powermax45 XP is the ability to evenly cut through metal that has spaces and gaps in it, such as rusted metal with open holes and grid materials. Many plasma systems will cut out and the arc will have to be manually restarted. The Powermax45 XP senses the gaps and automatically adjusts the arc, so all you have to do is move the torch across the metal to get a clean cut without retriggering the torch.
Removing spot welds
Once the main sections have been cut away from the trunk area, it’s time for the fun part: Removing the spot welds along the frame rails and quarter panel dropdowns. There are several methods for removing the spot welds, such as using spot weld cutters or grinding.
Removing spot welds is normally a hassle. Ideally, you should only remove the metal from the top layer, leaving the bottom layer intact. Because the spot weld is harder than the metal around it, it can be difficult to drill or grind through it. Spot weld cutters often punch through both layers of metal, damaging the bottom layer. Similarly, it’s not uncommon to grind through to the second layer, so it must be done very carefully.
Speaking of taking care when removing spot welds, the Powermax45 XP has a gouge setting, which creates a softer, wider arc. By using the gouge setting to remove the spot welds, getting through a spot weld in less than a minute is a breeze. Again, the ability to set the Powermax45 XP at 10 amps is essential with various aspects of a restoration project.
With a little practice, the technique is easy to perfect. A good place to start is on an old trunk pan or on extra parts. Experiment by holding the torch and gouging at various angles to perfect a technique that works. It’s key to get comfortable with the gouge setting before trying it on the final project.
Above all else, it’s important to remember that you’re not actually burning away the spot weld itself, but instead, removing the metal around the spot weld. And keep in mind that old automotive metal is not like new metal. It can be thinner and it may burn away quicker in some areas. Watch closely and adjust your torch movement, as needed.
The process outlined above has saved me countless hours of time. Spot weld removal alone is reason enough for any restoration shop to consider adding a Powermax45 XP to its toolkit.