I found an interesting method of cutting radii for sub-roadbed on you-tube. It looks pretty good, the one thing I am going to do is modify the way it is assembled, though. Firstly, I am using a lamination of 1/4" underlayment. I will put three of them together, giving me a 3/4" unit. Now, on assembly, I am gluing them together in a staggered formation . I am using 2.5 inch increments. This will give me an effective, solid splice as well as a pretty good gluing surface; so three pieces glued and clamped together; then sanded for a smooth consistent edge, as well as face. These will mate together for a nominal curve.
I will rip the plywood into 2X4 foot pieces, making it easier to handle; then layout the curves (radii) using the method and implement that he exemplified; then cut the curves out on a band saw, using a 1/2" skip-tooth blade. The same can be accomplished using a sabre saw, or a jig saw.
Finish by sanding, then put a coat or two of shellac, or the sealer of your choice. This will help much when you install the roadbed, giving it a highly effective gluing surface.
So, the only waste you will have is minimal, and you have an effective, efficient system.
Rich C.
could you post a link to the video?