Sorry, should have said 1/2" dia. PVC. I didn't have any problems with the round edge. Tapped some finish nails into the points you want to follow and then butt pipe up to the nails. Use some weights to hold pipe against the nails and then butt your pencil up to the pipe edge and trace away. No fancy gauges or templates needed. Worked great.

> Even when you join two pieces with a coupling this stuff is marvelously
> uniform and flexible, (1/2 inch is even more so) but it has no square
> edges. How do you know what edge (there being none) to guide your pencil
> along when you try to trace those curves?

> I suppose you could make a block of wood with a hole in it that holds a
> pencil perpendicular to your paper, or plywood panel, and slide that along
> your pvc pipe. You would have to make some allowance for the width of this
> block-and-pencil slider, but it should not be too hard to calculate. It is
> essentially the same process as setting up a guide for your router.