I'm prepping to install my rudder box. I'm using the Racelite gudgeons and pintels from duckworks. My question regards the screws, which will in part be under the waterline for exteded periods. Can I simple predrill the holes for the screws, then coat the screws in epoxy when I finally install them (to keep the wood from getting wet)? Or must I drill out an oversize hole for each screw, fill with epoxy glue and redrill the holes in the epoxy plug? Same question for installin an aluminum shoe to the keel bottom.
Dave
Coating screw threads during insertion will glue (slightly) the threads to the wood fibers in the pilot hole. Mostly the epoxy will get wiped off, as the threads enter the wood (and a big drip of goo runs down from the bottom edge of the hole), but some will remain to glue the screw in. A more effective method is a slightly oversize pilot hole, which is wetted out with epoxy (read using a pipe cleaner or syringe to get the inside of the hole good and wet) then the screw is inserted. This is 50% better then wetting the threads and a standard size pilot hole.
Bonding the screw (almost as you've described Dave) by drilling an oversize hole (130% of the shank diameter or bigger), filling with thickened epoxy then inserting a screw will improve pull out strength by about 200%. You don't have to wait until it's cured to insert the screw. You can insert right away if the epoxy is thick enough not to run out of the hole. Or you can wait until the epoxy is in the "gel" stage and slowly and carefully "screw" the screw into the very soft epoxy (wet the threads with fresh, straight epoxy).
Bonding the fastener will prevent moisture getting to the wood through the screw hole. If you just wet the threads and insert the screw you will not seal the wood fibers in the hole, well enough to prevent moisture from getting at it. If the boat will be in the water for extended periods, then bonding is the only good choice.