I tried a couple of patterns, some in multiple pieces, but wasn't happy with the results. I wanted a single seam down one side of the bell, and I wanted the mounting bracket to be integral. This is the layout I developed for this cowbell.
The tricky part is getting the angles of the trapezoids right correct. I'll post later about my approach, which worked well and was minimally annoying.
The dots are folds, and the solid lines are cuts. The solid lines with hashes are where I forgot and marked a fold as a cut. It's important to be clear, because with the welder's shield on and the torch throwing sparks, it's easy to get confused.
The length of slotted angle is supposed to be a guide for the straight cut along the side. I abandoned it immediately, as it was not helping me.
Any decent shop teacher would give me a D for those "straight" edges, but it was cut.
The next step was to grind the edges that will be welded nice and straight and flat, and brush all the old grotty appliance enamel off the inside.
Getting straight bends without a bending brake has been a challenge. What has worked least poorly so far has been to clamp firmly the fixed portion of the workpiece between two lengths of angle to keep it rigid, and then use a third length to force the bend. A box bending brake would work much better.
I clamped it closed and welded it up. Here's how it came out.
Looks nasty before cleanup! Grinding welds flush on sheet steel this thin is risky, so I didn't dare take them down completely. But it did end up looking quite presentable.
And in fairness, here's the ugly side.
Here it is mounted on my drum kit.
It sounds different from other cowbells I've played. The steel is 23 gauge, much thinner than usual, and I've opted for longer and narrow as a result. But it has a very clear distinction between low and high notes, and a nice ringing low tone.
