We had a task one time on a job to mortise out hidden door bottoms into a number of solid core doors. The doors were 3' wide X 1 3/4"thick. the mortise was 2 1/4" deep X 3/4"W X 35" long. At the time we were using PC 695 fixed base routers, plunge router were yet to be developed.
We had a solid carbide 1/2"dia. bit X 3 1/2" long. We set up guide rails clamped to each side of the door,extended out with stops at both ends to stop the cut. We made cuts of 1/8" depth on each pass. it took 2 people to do this as one had to hold onto the router with both hands, while the other switched it on and off and held the vacuum hose , like Pat (Quillman), says it is a very precarious setup, and a little tilt one way or the other means disaster. Especially when the bit is extended over 2" beyond the base plate.