Re: Torsion box router with a 4th axis.
To reinforce what Peter is saying, torsion boxes are NOT stiffer than a solid of the same dimension.
What people are often getting confused with is:
If you take the same amount of material (mass/weight) and make a solid or make a torsion box (or other large section), the torsion box will be stiffer.
Stiffness depends mostly on the material furthest from the neutral axis. Material at the center of a beam carries very little of the load and does not contribute to stiffness much.
If the epoxy is free, go for it. It will seal the wood very well. You can mill / route epoxy fine. Wear a respirator when sanding or machining epoxy.
7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)