@7xien I accidentally picked a second one that had a dot that skirted the inner line just perfectly. I'm trying to find other matches from the sets of cogs I have but, so far that's the only one
@neauoire A problem shared by a music teacher turned out to be a 'new' way of drawing cycloids. The screenshot is the result of a cyrcle going trough a 'hole' (inside it) all points moving to (and trough) the hole with the same speed. In your case we'll need 6 points. Here is the hole picture: https://www.youtube.com/watch?v=ZN4OlUDKFB8