I have been using balsa with either nylon pin hinges or CA hinges for my foam core wings. On the Gee Bee, I removed 3/16" from the aileron cut out in the wing & the same for the leading edge of the aileron. I then cut that pattern out of the balsa & angle sand them before installation. I also mark a true to center for both pieces. this makes sure the hinges line up as perfect of a straight line as possible to avoid warps in the control surface. To get a good angle cut and maintain that straight line, I use tape. In this case, I used 1/16" pinstriping tape on the edge and painters tape along the center line. With this taped to to bench, I run a sanding block until the sand paper starts to touch both ends of the tape in a straight line. I mark the point for the hinges and carefully run an X-acto knife on the center line eyeballing it horizontal to the flying surface as I cut deeper. I start with # 11 and then make a few paces with a # 2. This will work for either CA hinges or pinned hinges. For the nylon plastic hinge, Formula 560 canopy glue holds them in place. Some folks prefer 30min epoxy. I've found either one to be rock solid. If U R using pink foam on a park flyer size, U might get a good hold with out the wood, hinged directly into the foam, but, I wouldn't do that with beaded foam.