I have been trying to learn how to make a mortise and tenon joint using a simple jig. The jig is just a 2x4 with some stop blocks. I am making a 1/2 inch mortise 3 inches long in a 2x4 to make a frame for a shed door. I made several test mortises in scrap. I'm using a palm router with 1\4 inch up spiral bit. I have an edge guide on the router. I don't have a plunge router, so I still a hole to the depth with a drill. I then start the router bit in this hole. I route from stop to stop and in 1\4 inch increments until I get to the depth, 1 3\4 inch. Then I adjust the edge guide and cut a slot right next to the one I did. Sometimes it comes out good, but sometimes the router goes off and cuts into the edge of the material. It's very inconsistent. I get a nice mortise on one end of the board and then the other side is ruined. I wonder if I should be using a single 1\2 inch bit and try to cut the mortise income pass, instead of cutting two slots side by side. I then clean up the mortises with an oscillating tool. Any advice?