How to Install a Mortise Lock

Mortise locks are not as common as standard cylindrical locks, but they can have distinct advantages over their more conventional counterparts. Mortise locks are often sturdier locks that offer more protection from an intruder. In addition, many consider them to be more aesthetically pleasing due to their antique appearance. Whatever your reason for wanting to go with a mortise style lock, you should be aware that such an installation is no light task.

Things You'll Need

• Drill
• Spade bit
• Side cutting drill bit
• Pencil
• Tape measure
• Electrical tape
• Chisel

Instructions

Prepare for Drilling

1. 

   Determine the proper size spade bit. To do this, hold the spade against the widest part of the interior of the mortise lock. The spade's width should be just slightly wider. Be careful not to choose a spade bit that is too wide. If the spade bit is wider than the outer lip of the mortise lock then the hole you drill will be far too big.

2. 

   Hold the mortise lock against the door in the position that it will sit when it's installed. The entire lock should sit within the door including the outer lip when properly installed. This means that you will want to hold the lock so that the face of the lock is perfectly aligned with the edge of the door. Be extremely careful not to let any part of the lock extend outward beyond the door's edge.

3. 

   Make the first mark for the hole. This mark will indicate the height of the hole to be drilled. The first mark will be made above the interior of the lock as circled in red in the picture. This mark should be made below the hole which is in the mortise lock's faceplate and yet above the prong that is made to extend from the faceplate into the door.

4. Make the second mark for the hole. This second mark will also indicate the height of the hole to be drilled and is made identical to the first mark except it goes below the interior of the faceplate. This mark should be made in the exact same orientation to the faceplate hole and prong as the mark that went above the interior of the mortise lock in the previous step.

5. 

   Make the final mark for the hole. This mark goes at the back of the lock and indicates that depth of the hole to be drilled. Ideally, the mark should be made at the exact depth at which the lock will sit but it is better to have the hole be too deep than it is to have it be too shallow so keep this in mind when marking.

Drill the Hole

1. Measure the height of the hole that will be drilled. The height of the hole to be drilled is the distance between the two marks that you made in steps 3 and 4 of the previous section.

2. Measure the depth of the hole that will be drilled. The depth of the hole to be drilled is the distance between the door's edge and the mark you made in step 5 of the previous section.

3. 

   Make two marks on the face of the door's edge that will correspond to the two marks that indicated the height of the hole on the side of the door.

4. 

   Make a line down the exact center of the door's edge. This will be used to center the lock in the door.

5. 

   Tape the spade bit so that it will only drill to the appropriate depth. Do do this, take the depth of the hole to be drilled (measured in step 3 of this section) and mark the same depth onto the drill bit. Tape the drill bit from the base of the bit upward to this mark. This will ensure that the bit blade will be exposed only to the depth at which you need to drill your hole.

6. 

   Drill a series of holes along the center line that you made on the face of the door's edge. Due to the tape, you should now be able to drill the holes to the appropriate depth. The holes should be close to one another but the should not overlap.

7. 

   Take out the spade bit and insert the side cutting drill bit into the drill (refer to picture to see a side cutting drill bit next to standard drill bit).

8. 

   Cut out the remainder of the notch using the side cutting drill bit. Do not rush. This is the most delicate step of the entire process. Expect at least 10 to 15 minutes to perform this step properly. It is helpful to periodically try and slide the lock into position within the notch throughout this step to ensure that the hole is being drilled to the correct proportions.

9. 

   Insert the lock into the notch and trace an outline along the outer lip.

10. Remove the lock from the notch and, using a chisel, chisel away the section of the door within the outline until it reaches the depth of the lock's face.

11. Insert the lock into the notch and screw it in place.

Tips & Warnings

• Installing mortise locks is not for the inexperienced handyman. There is a very real risk of damaging the door if not done properly.