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A roto-zip would cut the plastic well. would actually cut it instead of melting it. better then a dremel or any other abrasive tools like the dremel. dremel would cut it but will melt the plastic and then you would have to debur the melted plastic. Just have to gave a good hand in cutting it out. Personally I would machine it. yet thats alot more work unless you know someone who has machining experiance . also pre-drilling the holes near the corners will keep it from a sharp corner and cracking. would leave a nice radius in the corners and more professional looking with rounded corners and smooth looking