How to draw this shape...

[Acorn]

I didn't understand your method at first, Acorn.
However, the xara file shows exactly what you mean.
I like it.

haakoo's method allows the curvature to be adjusted.
Your method gives a more rounded arc.

So, you too are deserving of a certificate.

Rik, thank you. I read more into your "exactly the same" part.

In passing, constant breadth rotors are use in pumps, GB 20 & 50p coins, Canadian Dollar ("loonie"), Wankel engines and for cutting square holes!
https://upload.wikimedia.org/wikiped..._Animation.gif



Acorn