Before trying to trim the door open it and examine the hinges.
Plane hinge side of door.
Step 2 use your ruler to measure 1 8 inch from the jamb to the start and end points on the door.
Plane the hinge or lock sides of the door in the same direction as the wood grain applying light pressure to remove very small amounts of wood at a time.
Hold a belt sander plane or power plane at about a 45 degree angle to the edge of the door and remove material to the witness line.
Complete one pass per stroke with a hand or power planer with.
The radius of the mortise is determined.
A hinge can often work loose binding the door against the frame.
Turn the door so.
Running the plane in this direction will create smooth cuts instead of chunky bumpy cuts.
On many doors the grain runs from top to bottom instead of side to side.
Immobilize it with a doorstop and plane it in place see step 3.
People usually try to plane off the edge.
The hinge master mortising jigs have been designed to route most of the various hinge sizes of todays door industry.
But for maximum control and to plane longer portions take the door off its hinges with a screwdriver or drill.
Test each screw by tightening it with a screwdriver.
That may be difficult on older painted doors.