Notice the notch at the top of the mortise. This is what happens if your router base plate is not square (as in a rectangular plate). I was using a jig I had made to guide the router, but because the router base plate is slightly rectangular, if I forget to flip the router around 180 degrees when I get to the opposite end of the jig, the router will cut in further than intended.
The solution is to spend the time to make a square – or better yet round – baseplate for the router. That way, it doesn’t matter how the router is orientated, it will always follow the jig properly.
