Well, I’m cheap lol, and have a Glowforge and Inkscape, soooooo, I made this from thick and medium clear acrylic scraps! I haven’t tried it out yet, and it’s very hard to photograph clear acrylic… but I think it’s going to come in handy! I’ll be trying it out tomorrow when I work on more pens!
Maybe it’s an optical illusion but the two sides shouldn’t be at 90 degrees as it appears. The whole thing should lie flat with the longer piece over one side and in line with the centre of the v. Slip the material up against the longer piece and run it down until it reaches the v of the other two pieces. Scribe a line and rotate your piece 90 degrees to scribe the other line which shows you where center is.
I had a similar situation a while back, and made a large circle and forgot to mark the center before I cut it out. So I made one of those out of 1/8” plywood:
