To get the thicnesses right, I had to add fillets to the corners of the empennage components. Today I have done 3 of them. Originally, the outer battens are given in T shape, 1" by 5/8". This leaves 3/8" empty. When you use 2x1/8" ply for corner guessets, it makes 1/4". if you subtract 1/4" from 3/8" you end up with another 1/8" void. About 1/16" on each top and bottom. Now, imagine I did all that in metric materials. This is why I had to add the fillets.
