Swingman wrote:

Also, at a drafting supply
store you can buy a various lengths of plastic strip that is
flexible, but can be bent in many different positions and will hold
its shape. I use one for non-radius, flowing curves like you mention.

Solid core electric wire works too. A short piece of 12-2 or 14-2 cable
retains the shape well and lies flat for easy tracing.

-- Mark