Knife Hinge Installation
Article - February 21, 2011
The latest Guild projects are nearing completion and I wanted to bring you up to speed on the latest happenings in the shop. Lately, I’ve got hinges on the brain! Of course, there are lots of ways to hang a door. But I have yet to see anything that matches the understated elegance of a knife hinge. When properly installed you barely know they are there, yet they are capable of supporting a remarkable amount of weight.
Now just to be clear, this isn’t a full how-to on knife hinges. I was only able to get a few shots that depict just part of the process. But I thought it would still be worthwhile to share my methods with you.
And so it begins….
Like other hinges, the knife hinge needs to be placed into a mortise: one in the case and one in the door. Our story begins with the case. The hinge leaf is located and scribed during a dry assembly. The key to success with this process is using shims. I don’t want to have to THINK about where the hinge is going to go. Instead, I want physical barriers that prevent the hinge from being anywhere other than where its supposed to be! This allows for a very systematic approach which is right up my alley i.e. “Marc-proof”! A card scraper makes a great shim and helps establish the gap between the door and the case. My small adjustable square helps me establish the set-back. A couple of steel screws hold the hinge in place while I scribe around the perimeter. Do NOT use your brass screws for this. Save them for your final installation. The case is then disassembled and the mortises are routed and cleaned up with a chisel.
The CA Glue Trick
The door mortise is fairly straightforward since the goal is to have the hinge flush with the outside edge of the stile. As long as the long part of the leaf is centered along the thickness of the door, you’re good to go. In order to keep the hinge in place while I scribe around the perimeter, I use a little CA glue to hold it in place.
With the hinge locked down, scribing around the perimeter is a piece of cake! I take light passes at first and eventually increase the pressure so that I end up with a nice deep scribe line. “But what about the glued hinge?”, you ask. A quick tap with a hammer pops it right off. The residue is easily scraped off the hinge and the glue spots on the wood will soon be routed away. I only use this glue trick on end grain. On face grain, there is a good possibility of tearing out the wood fibers (this is why I used screws previously).
Routing the Mortise
Now its time to do some routing. Obviously, this is a dicey proposition if you don’t add supplemental support. Two pieces of scrap stock clamped to the door work wonders. Also notice that the scrap is longer than the door is wide. Its a good idea to provide that extra surface area so you can approach the mortising full supported.
A 1/4″ spiral bit does all the grunt work, cleaning out the bulk of the stock. I do this part free-hand, making sure I don’t get too close to my line. This way I can come back with the chisel, drop it into my scribe line, chop down, and call it done. The end result is a perfect mortise for out hinge. Don’t underestimate the importance of a good fit here. An improperly mortised hinge will result in extra pressure on the screws, and over time could lead to the door sagging or even complete failure. So you always want to take your time with this mortising step.
The End Result
Like nearly all things in woodworking, what initially looks complicated is really just a simple series of steps. Once you know the steps, you know how to do it. And if you can mortise for a butt hinge, you can certainly install knife hinges. As you can see in the photo, this wall-hanging cabinet is nearly complete. I just need to work on the drawer and apply the finish. By the way, thanks to all of you for the great suggestions on what to do with those incredible quilted maple panels. You can see where at least some of the stock ended up.