I dont want to take credit for this idea because it's someone elses. But, Have you tried chucking your router bit in a drill press and drilling it into some nylon or UHMW thats clamped in place. Lube the void left by the router bit with liquid wrench or some other dry lube. Then remove the bit and chuck a rod that is to be used for the stylus. Then , with the stylus rod locked at the right height, fill the cavity with epoxy around the tip of the stylus rod. When it dries you will have a perfect copy of the cut that the router bit makes.
I tried it with the straight bit and it seems to work good. Havent really used it extensively tho