There are two good ways to make sheetmetal hat sections that curve in two planes. One is to start with formed angles, then curve each angle using a shrinker and stretcher, and join them with a cap strip. The other way is to start with angles that have an extra-long flange, shape them with a shrinker and stretcher, then form a second flange with a beading machine, and join the two “Z” shapes with a weld in the center.
Q
I’m in the process of renovating a 1949 Studebaker pickup. Like a lot of these trucks, the floor is rusted in the rear corners on both sides. The part of floor that’s damaged is stamped into a U-shape, with a mirror image piece spot-welded from the bottom. This forms a structural rectangular tube, which joins to the step well structure. The step and its support are available, but the rest will have to be fabricated.
I’m having a hard time figuring a way to make this with the multiple curves involved. I’d thought of making two Z-shaped sections for each half of each curve, but they would need to be shrunk on the vertical wall, and I’d still need to have a flange to spot-weld to a flat piece.
I also have to replace the lower edges of the doorskins and structure as well as the back couple inches of the front fenders. I’ve got patch panels for these. The patches come with a flange stamped into them to slide under the original metal. Since these doors and fenders have curves stamped in them, would this work, or do you recommend attaching them with a butt joint?
Richard Meck
Via the Internet
A
It’s not very feasible to bend a “Z” shape in two planes, so I’d suggest a couple of possible solutions. The term I used to describe the shape you need is a “hat” section. The easiest way to make it is to fashion the sides from simple angles folded from sheet and then attach a cap strip to join them. This requires making long welds on the top corners of the “hat,” which I wouldn’t recommend for a part that needs to be beautifully finished, but for a hidden structural part it is the easiest way to go. The cap strip can be patterned after the sides are shaped, and it will probably be a gradual “S” shape in the flat.
For a part that needs to be meticulously finished, a more elegant way to fashion the hat section is to make sheetmetal angles with one extra-long flange, shape the angles with a shrinker and stretcher, then form a second flange to point toward the center of the web on the top element of the hat. These flanges can be readily made in a beading machine with “tipping” dies. Of course, some “tuneup” work will be required after tipping the flange, but the advantage of this approach is that the top corners are made by bending rather than welding. This will give them a more uniform, rounded shape, and it requires only one weld, which is positioned in a location that’s easy to work, and it can be finished to perfection if desired.
The illustration should help clarify these two different approaches.
Regarding the overlapped versus butted seams, I’m a strong proponent of butt welding patch panels.
A lap joint can collect water from condensation inside the door, eventually leading to rust problems, and it’s much harder to do effective hammer and dolly work in the area that is a double thickness.
You can email your questions to Professor Hammer – covell@cruzio.com – or mail a letter to Covell Creative Metalworking, 106 Airport Blvd., Suite 105, Freedom CA 95019. You will receive a personal reply. Ron Covell has made many videos on metalworking, and they can now be STREAMED or DOWNLOADED from his website! Check these out at covell.biz, along with his ongoing series of workshops held across the nation, or call for a current schedule of workshops and a free catalog of DVDs. Phone (831) 768-0705. Also, check out Ron’s YouTube channel – youtube.com/covellron.
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