Installing a mortised lock

Embellishing your project with a mortised lock adds to both its functionality and appearance. Of course, it adds a little more complexity as well. Follow these simple steps to master the mortised lock.

Nearly all the steps of installing a mortised lock remain the same regardless of its application. We'll use a drawer lock to demonstrate this technique.

Start by marking a centerline on the top edge and face of the drawer front. Holding the lock against the face, center the lock pin (see drawing below) and mark both ends of the lock faceplate on the drawer front's top. (Centering the lock body instead of the pin may place the keyhole off-center if the pin is not centered in the lock.)

In your drill press, install a bit that matches the width of the lock faceplate. (See "Which bit to use" on at the bottom on the page.) Set your drill press depth stop so the lock faceplate will sit flush with the top edge of the drawer front, and drill both ends of the marked mortise, with the circumference of the bit just reaching the marked lines [Photo A]. By drilling the ends first, you ensure they will drill out cleanly. If an end is left until last, the overlapping bit may chatter, leaving an imprecise or ragged hole. Don't move your drill press fence—you'll need that setting for the next mortise.

Make a scoring cut on the edges of your mortise with a straightedge and craft knife. Clean up the shallow mortise with the largest chisel that will fit [Photo B]. Invert the lock to check the faceplate depth—if the mortise isn't deep enough, use a narrow chisel.

With the lock inverted in the shallow mortise, transfer both ends of the lock body to the rail edge [seephoto at top of the page]. After setting your drill press and bit to the same depth as the lock body, prepare to drill the deep mortise. Unlike the shallow mortise, begin drilling both ends of the deep mortise by centering your drill bit over the end lines rather than abutting the circumference of the bit to the edge. This allows the mortise to accommodate the squared edges of the lock body. Chisel and clean up the deep mortise to fit the lock body.

Using the centerline on the face of the drawer front, center the tip of the key and mark its vertical limits [Photo C]. Insert a filler shim in place of your lock while drilling the keyhole [Photo D]. Insert the lock, drill the appropriate pilot holes, and secure with screws.

To quickly and accurately mark the location of your strike plate mortise, generously coat the end of the bolt with a permanent marker, close the drawer, and turn the key to engage the bolt against the corresponding rail [Photo E]. With double-faced tape, center the strike plate over the mark and score the outline with a craft knife [Photo F].

Using the same procedure as with the lock faceplate, drill a shallow mortise [Photo G]. Mark and drill the deep mortise to allow for the bolt to fully engage when turned. If the bolt operates with a hooking motion rather than strictly vertical, you'll have to lengthen the deep mortise to accommodate the bolt's movement. Secure the strike plate with screws.

While drilling a mortise, a Forstner bit drills cleanly, without chatter, and the overlapping holes leave less waste to remove later with a chisel. For our project, however, we needed to use a hand drill to mortise the strike plate inside the drawer opening—and a Forstner bit won't accept a stop collar. So our second-best option was a brad point bit, which still allows for some overlap and can be marked for consistent depth with an ordinary stop collar. If you don't have a brad-point bit to match the plate's width, you can make it work by separating each hole by ¹⁄₄ " and chiseling away the remainder.