Contoured Patches
Quick and easy fitting reinforcement for curved surfaces
Some side reinforcement patches can be simple flat splints that don't have to fit precisely on a curved surface. But lots of times it's just not possible to get away with a flat cleat when you want to reinforce the inside of a crack repair.
I take a piece of 80 grit sandpaper and hold it over the the outside of the area I need to reinforce. Then I take one of my thick cork sanding blocks and simply and quickly sand the block to match the side:
This takes a surprisingly short time because the cork is so soft and granular that it sands to shape immediately.
My cork sanding blocks are 1/4" cheap cork material I find at auto parts shops and home improvement centers. It's sold as gasket material, or whatever. I laminate three or four layers and cut it up for handy sanding blocks.
Then, if I hold some 150 grit sandpaper on the curved surface I just formed, I can easily shape the back of a reinforcement cleat to match the inside curve of the guitar:
I find this method to be precise enough for almost all applications - - I can get the reinforcement patch fitted in almost no time at all.