You've seen these fairing sticks (used for drawing arches) before and they are super simple to make. I have a small one but, found a larger one would come in handy for my current project. Rip a strip of hardboard on the tablesaw so it is dead-accurate. Drill a pair of holes about 1/2" apart near each end. Cut a smaller piece to act as your locking slider and drill a hole near each end on it.
Tie a piece of line to one end, feed it through the slider, feed it through the holes at the other end of the stick and run it back to the slider. Tie the line off at the slider.
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And there you go. Here's a pic of the small one so that you can see the whole thing better.
Bow the stick and take the slack up with the locking slider. Once the initial stretch is out of the cord it will retain its form for extended times when you wnt to repeat a curve layout on several pieces. The 1/4" hardboard has enough of an edge to allow clamping in place before you draw your line. Release the tension and they store almost anywhere without taking up much room.
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