Laying out a cowbell, step by step

In my last post on making a cowbell from the side panel of an abandoned dishwasher, I didn't provide details of how to lay out the pattern. For that one, I used trig to figure the angle of the large trapezoids, then used my tablesaw mitre gauge to set that angle, and a bevel gauge to transfer it. Ridiculous.

This cowbell will be similar to the last, but where it was 6 inches long, this one will be 5 inches. The other dimensions will be the same: 3 x 1 1/2 at the mouth, and 2 x 1 at the back. The finished pattern looks like this:

I labeled the top, bottom, and over and under flaps of the welded side. The unlabeled side in the centre is where the layout starts.

I found this article, which suggests using a cardboard pattern. And once I started thinking about that, I agreed that the whole thing can be drawn more easily, accurately, and repeatedly without any trig or angle transfers. I used an empty cereal box for my patterns.

To draw the large trapezoid, I first marked the endpoints of a line that is 5 inches long. I labeled them as C and C'.

That line is the centreline of the trapezoid. The mouth is 3 inches wide, so I marked dots at 1.5 inches either side of C, square to the centreline. It's two inches at the back, so I marked 1 inch on each side, and then drew the lines.

I plan to make more of these in different sizes, so I made patterns for 5, 6, and 7 inch cowbells with the same mouth dimensions. (Of course I'll experiment with the mouth dimensions at some point too.)

I didn't make a simple rectangle pattern for the back and mounting bracket, but I should have and will next time. In this case, it would be 1 inch by 2 inches.

To draw the cowbell pattern on some scrap sheet steel, I inset the small trapezoid cutout from the edge of the panel and marked its four corners.

Then I aligned the left edge of the large trapezoid with the dots at the right edge and marked its other two points. This will be the bottom of the cowbell.

I used the small trapezoid aligned with those marks to mark the under flap.

The top and over flap were laid out in the same way on the left side of the pattern.

I dotted the fold lines and stroked the cut lines. As usual, I stroked where I should have dotted and hashed the line to compensate.

Add a rectangle to the bottom, which will fold to become the back, and three to the top for the mounting bracket. Like this:

I want to try cutting this one out with a cutting wheel in the angle grinder. I've marked my intended cuts in the photo below. I'll post later about how it turned out!