Folding a sheet of metal in a straight line is one thing, but how does one fold multiple curved lines into a sheet of aluminum without fancy machines? [John] demonstrates how to do exactly that with little more than hand tools and a fair bit of patience. The secret is drilling a lot of small holes along each fold line.
First, a bit of background. [John] wanted to fabricate a curved piece of aluminum as cover that would match the sleek aerodynamic lines of a Belly Tank Lakester. The trick is that there isn’t a single straight line to be found, and the fold lines are all curves. How can one do such folding with only hand tools?
[John] found that fabrication was possible by drilling small holes all along each fold line, then carefully bending as needed. The line of holes weakens the metal, acting like a score line, and allow the required curves to be made cleanly. There’s some finishing work and straightening involved, but the hard part of making the actual folds is taken care of.
One method that didn’t work was cutting a shallow groove in the metal to create something like a pre-scored fold line. [John] tried this and found that while the metal does indeed fold along the weakened line, the aluminum tends to crack in the process. When making a line of holes instead, the metal between each hole bends nicely.
This technique does mean the finished part ends up with small perforations along each fold, but the part is mounted on the bottom of the car and [John] says that he’d have to look quite closely to notice. A little polishing goes a long way, too.
We have covered many ways to bend sheet metal and while machinery exists to do it exceedingly well, great results can be had with little more than simple tools and some patience.
Watch [John] go through the process in the video embedded below, or skip to 7:55 if you just want to see the end result.
This looks surprisingly good for such a method. I know how difficult it is to make some of those shapes, even with proper tools. Or maybe it’s just me. I might have to try it sometime.
And as we all know, the air holes make it faster.
What about no through “holes” ?
If scoring a groove doesn’t work, there’s a method from arts and crafts: you can start the fold by pressing and dragging a ballpoint pen along the line. That way you can fold little boxes or fancy shapes out of soda cans or thin walled soup cans, or emboss artwork that shows up as raised forms on the other side.
The same technique should work with thicker sheets – you just need a bigger stylus and apply more pressure. You could make one out of a steel rod and a bearing ball – drill a hole in the end, drop the ball in, and hammer the sides in just slightly to capture the ball.
Alternatively, you can take a blunt chisel and a hammer, and tap along the fold line.
If is not a structural part aluminium, a good pass in the kitchen oven at max helps al lot the ductility, unless it is electron and few aeronautical grades, that do the exact opposite: it gets harder when heated (annealing)
There is a well established artisan technique using a variety of English Wheels. I’ve seen tear drop motorcycle tanks (made in two halfs) and fenders only using this method.