Tips on Mortising a Replacement Door

• Mortising for hinges, knobs and locks can be tricky.Door Knob image by Edward B. from Fotolia.com
  
  Mortise joints have been used in woodworking for centuries. Today, mortises are primarily used to provide clearances for hardware, such as hinges and door knobs. They are used in three places on doors: the notches in the hinge edge of the door that accommodate the hinge plates, the holes bored for knobs and the holes bored for knob latches in the side jamb. Replacing a door in an old jamb can be tricky, and proper mortising is key.
  
  

Making the New Door Match Up

• When placing a new door into an old jamb, it is easiest to use the mortises already on the jamb as templates for the new door. Stand the door upright in the jamb, spaced 1/4 inch off the floor, to match up the door to the existing mortises. Have a helper hold the door in position. Mark the top and bottom of each hinge along the edge of the door for proper hinge height placement. Mark the center of the knob striker and deadbolt receiver plates along the knob edge of the door to mark the correct heights so that the new hardware will match the jamb.
  
  

Outlining Mortises

• Having a clear guideline makes chiseling and boring much simpler. Use half of a hinge as a template to mark the spine, or hinge edge, of the door for hinge mortising. Always use the hinge you will be hanging the door with to avoid confusion on the size and placement. Consult the paper template that comes with your new door hardware to space the holes for new knobs and locks. Check your knob for backset. The backset is the distance from the edge of the door to the center of the doorknob. Use the correct mark on the template to indicate the center of the knob. Mark the mortise holes for knob and deadbolt latches in the center of the door's edge to avoid splitting or breaking through the face of the door when boring. Matching this hole to the center of the existing striker, or deadbolt receiver, will allow the new knob or lock to function without adjustment.
  
  

Cutting Mortises

• Boring and chiseling are two common methods of cutting mortises. Use sharp chisels and drill bits to provide a clean cut. Dull tools make the progress slow and can damage the door, and are more likely to cause injury due to the additional force used to get them to cut. Never force drill bits and hole saws through the door. This can lead to splintering, and heats and dulls the bit. Always cut away from yourself when using a chisel. Use the widest chisel you can to make your cuts. Fewer cuts means a smoother mortise and a better-fitting hinge. Use a light hammer or wooden mallet for driving your chisels to minimize chipping and gouging.