Lee Valley used to make a corner chisel unit that could do just that. At the moment you have to carefully chisel out the corner. Alternatively wait for the tool to be made again by smartboxmaker. com Go to that web site supposedly he will have the tool available soon. He promised it over a year ago and it is late. Andrew Crawford makes mainly side mount hinges and locks for real high quality boxes. The hinges are truly the best. If he has the corner chisel available again it will be a good one. Good luckIm trying to get square outside corners in aspire (9.514). See attached pic. Red arrow is pointing to my problem. I want to get that as a square corner. I have tried all types of things and cannot get it. The inside corners are great just the way I want it. Any ideas on how to achieve this?