Hi Jim. The original Estes K11 kit used BT20 (18 mm ID) tube. I am using 65 mm heavy wall paper airframe tube -- so 3.6X (4X to 1 significant digit). For sentimental reasons I am building it to look like an upscale of the 1970s model rocket, not a downscale of the 1940s JPL sounding rocket -- so no tail cone. I may not even fill the wood grain on the nose cone or the fins.
I am keeping it as simple as I can. Single deployment. No avionics. I am overbuilding it, since I plan to use if for my L1 certification attempt some time this summer. Simulations look good with motors from a G54 to H250. At the top end, Open Rocket claims it'll break 1000 meters on an I200.
Rob, I am not sure it would solve my issue. I'm using Nitto DS tape. I am getting good adhesion, and I don't have a problem getting the work pieces off the waste board. I want something I can cut into that I won't have to pick out of the flutes of the end mill. Something friendly to plywood.