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Installing a Mortise lock on a Wood Door

Mortise lock prep, typically referred to as 86 prep, is a type of door prep that involves cutting a mortise (a rectangular recess) in the edge of a door to accommodate a mortise lock. Mortise locks are commonly used in commercial buildings and high-security residential settings because they offer superior strength and durability compared to other types of locks. Here are the steps involved in mortise lock prep in a wood door:

Step 1:

Measure the location of the mortise lock on the door. Mortise locks are typically located approximately 40 inches from the bottom of the door, but this can vary depending on the specific lock and door.


Mark the location of the mortise on the edge of the door. Use a square to ensure that the marks are straight and level.

Step 3:

Use a mortising jig or template to guide the mortising process. The jig will ensure that the mortise is the correct size and shape.

Step 4:

Use a mortising machine or a chisel and hammer to cut the mortise. Be careful to stay within the lines of the mortise marks and to make the mortise the correct depth for the lock.

Step 5:

Test-fit the lock in the mortise to ensure that it fits properly. Make any necessary adjustments to the mortise as needed.

Step 6:

Install the lock in the mortise according to the manufacturer's instructions. This typically involves attaching the lock body to the door with screws and installing the latch and strike plate.


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