How to Install a Half Mortise Lock
Locks can be a bit tricky to install well on boxes and cases. They typically require multiple mortises of varying depths, and things don’t always line up quite right. Measuring can work, but I find it best to use the lock itself to lay everything out.
I recently installed an antique half mortice lock in an offering box I made for a new church. I had watched your video first and it helped immensely. Boy those things are fiddly to get the lid piece just right.
Thanks for posting this! I’m making a keepsake box for a granddaughter with this kind of lock. Wrestled with using a router for this work but the challenge of getting fences set, etc. seemed tougher than doing it this way …until I tried. About 14 minutes in you are doing the cut-out for the lock itself and we don’t get to see the start of that. Your video picks up with a couple cuts on either side of the opening that ultimately go away. 1. How to be accurate with chisels in the dimension for the thickness of the lock. 2. Do you whack the chisel to cut the sides in deeper? That must be done in steps I presume? 3. What were those cuts I mentioned earlier and why did they go away?
At 10:13 I begin the layout for the mortise for the brass top/back plate. This is going to be the most critical mortise layout as it will be visible in the final piece when the lock is installed. I then proceed to make the mortise for the top of the brass plate.
At 13:22, after the mortise for the top brass plate is done and I can register the lock body flat on the inside of the box, I lay out the mortise length and width for the lock body with a pencil (answer to your Q3). This mortise is not critical that it be a super tight fit, in fact it’s better if it’s not super tight. This will allow some room around the inner lock body for minor adjustment of the lock fit. Since this mortise will never be seen, it doesn’t have to be perfect.
At 13:58 you can see the layout lines for the lock body. Again, this inner mortise doesn’t need to be perfect in length, width, or depth. To gauge the mortise depth (answer to your Q1), I set a marking gauge fence on the front face of the brass face plate, and set the point/knife of the gauge by eye to be a hair deeper than the total depth of the lock (face plate plus lock body). Again, this depth isn’t super critical, it’s just providing clearance for the lock body. It’s better if it’s slightly deeper than necessary to avoid interference of the mortise and lock body when doing any minor fitting of the face plate later. Just don’t go so deep that there isn’t enough thickness left, but setting it by eye is good enough.
To cut the inner mortise for the lock body, I do chop, GENTLY (answer to your Q2). I chop well inside the layout lines, remove the waste by paring, and widen/deepen the mortise gradually in stages. The final cuts are all paring cuts down to the layout lines and the mortise for the lock body is completed at 14:38.
At 14:55, after the mortise for the inner lock body is done, I then do the layout for the brass back plate.