Hello all. In the process of making a winter dream tarp (DIY Gear Supply template) and I wanted to share a fast and easy way to make the catcut curves.
I use a 5' long and a 10' long piece of 1/2" plastic water line to make short and long curves. Using 2 mitten hooks and some string, I make a "bow" with the pipe. I measure the depth of the curve I need from the center of the pipe to the string. Once the depth is set correctly, I lay the bow on the silnylon at the right points and carefully trace the curve with a marker. A couple of books placed on the bow will keep it stationary.
Once the depth of the curve is set on the bows, it takes very little time to make and cut the curves with a razor blade. I also save time by placing both pieces together and using tape to to hold them to a piece of 4x8 hardboard. A new razor blade cuts thru both sheets easily - just go slow and cut a few inches at a time.
Cutting both sheets at one go ensures that the catcuts are the same for both sides (mirror images). If you don't have any hardboard, a wood floor or some concrete will do - you'll need to use scissors instead of a razor blade. Cuts in the wood floor don't go over very well with the spouse and concrete dulls the blade too quickly.