If you have an older house with knobs that slip, latches that are stuck inside the door, or other minor problems, then you should follow these instructions to remove the lock, dis-assemble it, clean and perform minor repairs.
Step 1: Meet the mortise lock and door knobs.
This mortise lock set is installed in a 1930 colonial in the Boston area.
Notice the set screw on the base of the knob on the right. This screw should hold the knob securely to the spindle when you turn the knob.