When he first encountered a flexible curve template many years ago, the author was unable to locate a commercially available one, so he designed and built his own. Although such templates can now be purchased from woodworking stores, they have some limitations compared with the author’s design: they cannot be shortened to fit into tight spaces, and they are not fitted with clear polycarbonate battens, which make the tool much more versatile. The tool’s aluminum parts may be machined or hand-cut.
Years ago, a boatbuilder friend of mine showed me a flexible curve template. It consisted of a thin spring-steel plate about 8' long connected to a series of stand offs that in turn were connected to a number of slotted flat pieces of metal. The slotted pieces were tightened to the stand offs with thumb screws to hold the spring-steel batten in place, thus picking up whatever curve the batten was formed into.
Over the years I kept my eye out for one of these gadgets but was unable to find one—although there are now commercially available ones that have some limitations as described below. While trying to install some curved frames inside a cockpit, I got frustrated enough to build my own version of the flexible template. I had previously made spline battens out of polycarbonate to use with some lead drafting ducks I made. I found them to be very useful and nearly indestructible. I therefore used this material for the batten part of my shop-made template.