Installing a Half-Mortise Door Lock

During the 18th century, locks were often
used on casework to secure spices, important
papers, jewelry and other valuables. The most commonly
used type of lock fits into a half-mortise (a
mortise that’s open on one side).

I use a combination of power tools and hand
tools to create those half-mortises–the kind of
work I particularly enjoy. It’s not a difficult task, but
after installing dozens of these locks, I’ve realized
that it’s important to do each step in a particular
order.

 

Why use locks today?

I made this 18th century corner cupboard the way it would
originally have been built–with half-mortise locks, instead
of handles or pulls. The key serves as a handle, and the
lock’s bolt works as a catch. If you’re building a period
piece, you’ll probably
be installing
similar locks,
because they’re
often an essential
element of a
piece’s design and
history.

While most
folks today don’t
need to keep
everything in the
house under lock
and key, locks
do have a place
in contemporary
furniture. A lock
adds curiosity and
mystique to a door
(especially if you
cannot remember
where you hid the
key!). And without
a pull or handle,
a door can have a
much sleeker look.

 

Buy the right lock

The first step, of course, is to get the correct lock.
That’s not as easy as it may seem. Locks for doors
and drawers often have two keyholes positioned
90° apart, which makes this type of lock interchangeable;
it can be mounted vertically for a door
or horizontally for a drawer. Ordering a lock for
a door can be tricky, because locks come in right
hand and left hand versions. Unfortunately, this
designation is not universal among suppliers, so
you’ll need to inquire which is which when purchasing
the lock.

The next item to address is the lock's size. Size
determines the distance between the edge of a
drawer or door and the keyhole and escutcheon.
The larger the lock, the longer this distance will be.
For doors, the width of the stile will determine the
maximum size of the lock.

Selecting the right escutcheon is just as important
as selecting the right lock. Escutcheons are
often made of brass, but you can make one from
contrasting wood or an old ivory piano key. During
the 18th century, escutcheon styles continuously
changed in keeping with furniture styles. If you
want your cabinet to look authentic, find some photos
of genuine pieces made in the same style and
compare their escutcheons with what's available in a catalog or online. I usually order an escutcheon from
the same company that supplies the lock to make sure
the lock's key will fit the escutcheon.

 

Position the lock

OK–you’ve bought the lock, and you’re ready to
install it. Let me walk you through how to do this on
a door (the procedure for installing a drawer lock is
very similar). First, carefully fit the door and install
the hinges. Next, determine the lock’s exact location
by positioning its escutcheon. The distance of the
escutcheon’s center from the door’s edge is a given–
it’s the distance from the edge of the lock to the pin
on which the key pivots.

The best height for the lock isn’t as obvious. From an
aesthetic point of view, I prefer to position the escutcheon
above or below the door’s centerline–not right on
it. If the lock goes on the upper door of a large piece,
I’ll probably place the lock slightly below center, so the
key is easier to reach. If the lock goes on a lower door,
I’ll place it slightly above center, for the same reason.
In either case, make sure to locate the lock so that the
lock bolt will not interfere with interior shelves.

To determine the lock’s exact height, stick the
escutcheon to the door stile with double-faced tape
(Photo 1). Step back and take a look at how the
escutcheon balances with the other brass hardware and the lines of the cabinet. I usually try moving the
escutcheon up or down a bit, just to see how it looks,
and wait a day before making a final decision.

Once you’re satisfied with the placement of the
lock, mark crosshairs inside the circular opening of the
escutcheon to indicate the location of the pin on which
the key pivots. Remove the door and draw a horizontal
line through the crosshairs (Photo 2). To accurately
draw the vertical line, measure the distance from the
edge of the lock to the center of the pin (Photo 3) and
mark this distance on the door (Photo 4).

 

Cut the mortise

Next, drill a hole through the stile at the intersection of
the crosshairs. Select a drill size which closely matches
the diameter of the keyhole in the escutcheon (Photo
5). Flip the door and lay out three lines for the lock’s
mortise on the inside face of the stile. First, measure the
distance from the pin to the top edge of the mechanism
(Photo 6) and mark this on the stile. Measure the mechanism’s
width, including the brass edge plate (Photo 7)
and mark this on the stile (Photo 8). Lastly, measure the
full height of the mechanism and mark its bottom edge
on the stile. Shade in the mortise (Photo 9).

Before you cut the mortise, use a marking gauge to
lay out the far edge of the recess for the lock’s backplate.
Set the gauge directly from the lock (Photo 10), then scribe the line (Photo 11). Why do this now? The
reference surface for the gauge will be removed once
you cut the mortise.

I use a laminate trimmer with a 1/4" bit to rout the
mortise. Place the lock on the router’s base and set the
depth-of-cut slightly more than the combined thickness
of the lock mechanism and the plate (Photo 12).
Clamp the door securely to a solid workbench and rout
the mortise up to the layout lines (Photo 13).

 

Cut two recesses

Place the lock in the mortise, then use a knife to mark
around the lock’s backplate (Photo 14). Carve a recess
for the plate by paring across the grain with a chisel
(Photo 15). You could mark the depth of this recess
with a gauge, but I just do it by eye, checking as I go.

Next, position the lock in the mortise and mark
around its side (Photo 16). A series of shallow chisel
cuts across the grain (Photo 17) make it easier to pare
this shallow recess (Photo 18). Elongate the keyhole
with a rat-tail file to accommodate the key.

Replace the lock and drill pilot holes for the screws.
Remove the lock and run steel screws into the holes
(Photo 19). Steel screws are much less likely to break
than brass screws, so I always use steel screws first, to
tap the holes. Remove the steel screws, replace the
lock, and install it with brass screws (Photo 20).

 

Cut the bolt mortise

Next, cut a mortise in the cabinet’s stile to accept the
lock’s bolt. First, extend the bolt and mark its location
on the stile, leaving about 1/16" leeway on either side
of the bolt (Photo 21). Measure the distance from the
face of the door stile to the bolt (Photo 22) and mark
this distance on the cabinet (Photo 23). As you cut the
mortise, gradually work your way toward the face of
the cabinet (Photo 24). The final shaving from the mortise
allows the bolt to slide smoothly into place.

 

 

This story originally appeared in American Woodworker April/May 2010, issue #147.

April/May 2010, issue #147

Purchase this back issue.

Click any image to view a larger version.

1. Begin by placing the lock’s escutcheon on the door using doublefaced
tape. Mark the center of the escutcheon’s circular opening.

2. Remove the door and draw a line through the mark.

3. Measure the distance from the edge of the lock to the pin that
receives the key.

4. Mark this distance on the door.

5. Drill a hole through the stile at the intersection of these two lines.

6. Next, lay out a mortise to receive the lock’s mechanism. Measure
the distance from the center of the pin to the top of the mechanism.

7. Measure the mechanism’s width, including the brass plate.

8. Transfer both measurements to the inside face of the door.

9. Mark a line for the bottom edge of the mechanism and shade in
the mortise.

10. Before cutting the mortise, set a marking gauge to the width of
the lock’s back plate.

11. Mark this distance.

12. Adjust a laminate trimmer slightly deeper than the combined
depth of the lock’s mechanism and back plate.

13. Rout the mortise up to the lines, freehand.

14. Place the lock in the mortise and scribe both sides of the back
plate.

15. Pare to the lines, going across the grain to prevent tearout.

16. Place the lock back into the mortise. Scribe around the three
sides of the back plate’s edge.

17. To aid in paring this recess, make a series of shallow cuts using
a chisel.

18. Then pare across the grain.

19. Mark the lock’s screw holes, drill pilot holes, and drive steel
screws into the holes.

20. Remove the steel screws and install the lock using brass screws.

21. Place the door back on the cabinet and mark the location of the
lock’s bolt.

22. Measure the distance from the front of the door’s stile to
the bolt.

23. Transfer this measurement to the cabinet’s frame.

24. Cut the bolt’s mortise. Done!