. . . without chipping paint from the faces of the door or -in the case of planing the bottom of a door- without splintering the wood at the corner?

(all 100yr old tenements round here)

many thanks

Tim Mcgregor, April 2007

Use a Stanley knife and score the paint along your proposed edge. Just make sure you cut right down to the wood and don't plane below that line. If you need to take off more wood cut a new line.
As for the bottom, work from each side to the middle. You'll only get splits if you plane to the edge of the grain.

Big Softy, April 2007