Metal shaping is one of those things that seems like black magic to beginners. There really is a science behind the process that takes quite some time to learn and understand. The quickest and easiest way to understand how metal shaping works, on the granular level, is by comparing it to pizza dough. The more you stretch it out, the thinner it gets. The excess material has to go somewhere (in the pizza’s case, its the rolled up crust). The more you shrink the metal, the thicker it gets. Again, it has to “go somewhere”. I decided to demonstrate a great beginner project for gaining experience in metal shaping by making a panel blister out of a 12″x12″ piece of 5053 .035 aluminum. This project is great to help you understand the process and is pretty straightforward.
The first step is to mark out a rough shape with a bullseye in the area where you want to be shaping. I made my shape a little larger than in this first photo, but it gives you an idea of what you want to draw up. The first tool you will need is a sandbag (also known as a panel beater bag) and a plastic or nylon teardrop shaped mallet. The bag should be filled about 60%-70%, and the part you are shaping should be centered on the sandbag. The idea of the sandbag is that the bag supports the edges of the panel, as you hammer on your bullseye, and will give in the center as you stretch the metal out.
Once the panel is set up and you have your hammer in hand, picture the one thing that makes you the most annoyed and start swinging away!! Working with aluminum does take a little less brute force than steel, but it does take a lot of hits to get the metal to start doming. The broad side of the hammer will contact a larger patch and requires less hits to cover the panel, but it won’t stretch the metal out as much as with the pointed end. A rule of thumb is to stay reserved and work your way up to the stretch you want in the metal.
As you can see above, at this point, you’ll probably be pretty scared and disappointed in the condition of your once flat panel! Don’t toss it in the trash, just yet! The first step is to use some good old fashion elbow grease and flatten the edges of the panel with your hands. Most times, you can get 70%-80% of the waves out by carefully bending the edges back into place. Don’t get too crazy about it at this point, just get it somewhat flat again.
From here, you will want to walk over to the English Wheel. Insert the panel area of the domed up metal, where you made a lumpy mess. Tighten the lower wheel, so it has very very light pressure on the panel, and work your way ONLY across the raised area of the panel. Be sure you are keeping your tracks as close as possible. Below is a picture of what your tracking pattern should look like on the panel. Once you get across the domed area, you should notice the panel gets easier to push through the wheel and a lot of the raised areas have been smoothed out. From here, I would rotate the panel 90 degrees and repeat the process. Once you’ve run the panel through a few different angles, you can tighten the bottom wheel slightly to smooth out the surface more.
At this point, you should have a panel with wavy edges and a domed section that is starting to smooth out. If you want more dome in the panel or you see some low areas in your dome, you can take the panel back to the beater bag and hammer the shape out more. This obviously will require another run through the english wheel, where you can tighten the pressure up more to fine tune the shape of the domed area.
Once you’re happy with the shape and the surface is fairly smooth, you can correct the potato chip effect on the edge of the panel. These areas are wavy because the metal has been stretched so far in the center that it has pulled the flat areas out of shape. This process is pretty quick and easy. Turn your panel upside down and put it in the English Wheel. With moderate pressure, run the wheel over the wavy perimeter of the panel, while putting light pressure down on the edge of the panel. You should feel the panel almost “pop” back flat after a few rolls back and forth. Repeat the process on each side, until your panel is pretty flat around the perimeter. Take care that the wheel pressure isn’t too high and that you don’t press down on the panel too hard, as you can overstretch the edges and send your progress backwards!
The final process is to use a sander with 80-180 grit paper and a soft pad or a vixen file to highlight the low spots on the domed section of the panel. You can hammer and dolly those areas up, or use a bullseye pick to carefully lift the small spots up until they’re level and the sander or file touches all surfaces of the domed area of the panel.
Finish and smooth the transitions with the soft pad on the sander and you’ve got yourself a nice panel blister to use for clearance on your project car….or to show off to your friends! Obviously, there is some time involved in this process and practicing how to make panel blisters over and over will speed up the process. But, the main goal with this process is to get you comfortable with shaping and finishing metal. Once you get really good, you could potentially polish one of these aluminum panels to a mirror shine!