I saw this picture online: https://imgur.com/t/aiko/mu96ohu and I thought it was too cute a technique not to try out for myself. I did a couple of minutes sketching in Inkscape, and then had it lasercut shortly thereafter.
Here’s how to use it. First, simply drive a couple of nails through your favourite table or work surface:
Then, using a pen, draw out the circle while keeping the ruler pressed against the two nails:
You should end up with a perfect(ish) circle that passes smoothly through both nails.
I’m going to try to remember this trick, I can see it being useful for laying out parts for machining, or to make shapes based off existing features.
Files here for anyone that wants to make their own: