Many times I have cut durable templates from aluminum siding trim rolls. Its cheap and if you polish the edges the razor blades slide along nicely. For really irregular curves I pin a .032 diameter of piano wire to the shape of the curve I am looking for then use it as the guide for the razor blade. I only use single edge razor blades they seem to hold up better and for me buying them in bulk are cheaper than the #11 blade.

Dennis