Okay I'm getting in over my head here but I've decided to build my own custom frame, I've got almost everything worked out other than the tube for the fork and the bottom bracket. I want to know if I should fabricate, repurpose, or buy new/used? I'm confident I can install them myself but not so confident that these components can be made with hand tools.
yes, and then the same for the bottom bracket to the head tube.. and then 1 tube for each seat stay and 1 tube for each side of the rear fork, I'm thinking of using the tubes then custom wrapping the joints in carbon fiber fabric to join them rather than going with the scotch weld bonding route... I will how ever be using that or something else to bond the bottom bracket headtube and seattube though. So does this sound viable? No kit not nothing.. home made frame jig to duplicated this frame I have.
I can't comment on your proposed joining method, but I'm not sure you're going to be happy with the down tube being two 1/2" tubes. To get similar stiffness to a normal down tube you'd have to go larger.