Most of the recent articles on installing hardware such as knife hinges, or recessed pulls seem to advise using a router freehand and then paring the waste with a chisel to the scribe line. My bathroom cabinet construction rasied questions about installing hinges. That is a decent way to do it if you have a large surface. If you have the edge of a door it is difficult to steady the router.It is risky ...if you slip you ruin the door...ouch. If you have several doors to build or flush laches to install, make a simple jig to guide the router.
If you just have a couple to install...this tip works well. I can't remember ever seeing it published though.
Locate where the hinge or hardware is to go.
Install it using a Vix bit to center the holes.
It is nice to have an extra set of screws and hinges to use.
Surface mount the hinge using the screws (2 are required for stability)
With a sharp knife scribe around the outside of ths hardware edge.
Go deeper with each pass.
Remove the screws and plant the chisel edge in the knife scribe.
Go light near the edge.
Pair out the center using a chisel.
This is quick and accurate since you are scribing and cutting to the actual piece. THe secure attacment using the screws allows the control of both hands. No pencil lines to deal with and inaccuracy.
Don't you hate when the phone rings and your freehanding the router