Saturday, September 8, 2012

[Schoolbox] - The Half-Mortise Lock

In the last post, I began dovetailing the sides of the Schoolbox. Mission accomplished! All the corners are fit, and I'm pleased with the results. Are they perfect? Not by any stretch. But I think I'll be able to deal with the small errors that were made. I chose not to write about it beyond some helpful tips for dovetailing, but I'll post pics when I do the final assembly. I am also going to reserve special post for the most frustrating part of the box to date. The keyhole escutcheon.

So this post is dedicated to the installation of the half-mortise lock. I took a class not too long ago at the Philadelphia Furniture Workshop and my teachers (Mario Rodriguez and Alan Turner) have taught me well. I was able to recall some of the valuable lessons they passed on and apply them for this build. Install the lock prior to assembly. Always practice the install in the same thickness and material before the actual install. These were just a few of the many.

What I found interesting is how little information is out there about installing a half-mortise lock. Fine Woodworking had a decent article by Philip C. Lowe. I found a few online hardware retail sites that had decent instructions. And Woodcraft had a short video, but that's about it. All of them were helpful in parts, but seemed to be short on some of the details in one way or another. Even Chris Schwarz mentions that no one taught him how to install in "The Joiner". So this seems to be a skill with some common steps but adapted by the woodworker by trial and error. So I cut a sample pine board and worked out an approach.

So it is with my very limited prior experience, reading the scant number of articles I could find, and a few practice attempts that I present my method of installing a half-mortise lock. I'm sure there are many better ways to do it, but this one is mine. Please feel free to suggest better ways if you've got 'em.

First step that everyone seems to agree upon is to find the center of the box and mark in pencil. After this the steps begin to deviate. Do this on the front, top and back of the box front.

Marking the center of the box. This picture also shows the mark out for the lock body.
I cover that below.

Next I mark out for the width of the lock body. I do this by placing the lock on the top of the panel and aligning the key pin (or post) with the center line of the box front. Most instructions do remind you that some key pins are not in the center of some locks. So the lock is installed by centering the key pin.

With the key pin on the center line, I use a small combo square to lay out the width of the body assembly in pencil. In my practice attempts, I was overly concerned about getting this measurement super tight. However, too tight here meant I had trouble pulling the lock in and out for fitting. So I found that you can leave yourself a tiny bit of room here.

The key pin (or post) is used to center the key in the panel. Not the lock itself. With the post on the center line I use a small combo square to mark out the width of the lock body.

The next step is to mark the distance from the top of the box front to the key pin. I do this with my wheel gauge and make a mark on the back of the box front. This sets the location of the key hole. I use a scratch awl to mark the position of the keyhole and use the same diameter drill bit and drill the hole on the drill press.

At this point I also mark out for the width of the lip, which is the distance from the  back of the lock to the front of the lip.  
Marking out for where the top of the lock. This is one of the most crucial measurements. Take too much material here and the lock and box will not meet tightly. 

At this point I cut a series of relief cuts for the removal of waste for the lock body. This makes the waste removal much easier. In some references, the waste is removed by forstner bit, straight router bit, or directly by chiseling it out. I haven't tried these methods yet, but this one seems to work just fine.

A series of relief cuts to make waste removal easier.

It's important when paring out the waste that you continuously define the edges of the marked out area after a few paring passes.

I've defined the area to be pared out and continue to define that boundary every few paring passes.

Almost to the bottom for the lock body. At this point I switched to my small Lie-Nielsen router plane.

Once the lock body fits and the back plate and the lip fit snugly against the back and top AND the post fits in the pre-drilled hole, the next step is to mark them out and very carefully remove the waste. Enough for just the thickness of the back plate and lip. In my practice runs I tried a number of methods. The one that seemed to work best was to pare a sliver for the lip just to establish an edge and then switching to the router plane. The lip is fussy work, so go slowly and plan shop time when you are not in a hurry. The recess for the back plate should go very easily.

Here is the finished cutout. I seem to pick up alot of discoloration when using the router plane. However it was very easy to clean up with a few light passes with the block plane.

Here is the final product. A little gappy on the left hand side but I believe the fit to be tight enough with the human eye. This picture is more of a closeup.

Overall I think the locks fits pretty well. I will deal with the keyhole eschtcheon in the next post. Thanks for reading.


  1. Hey John, Nice explanation. I still need to comlete the last corner and start the lock mortise. It shoudl be easier for me now. Thanks for the blog post.

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