Wedged Through Tenons
If you are looking for the piece on linen fold panels, please click HERE.
During a recent remodel of our house, I enlarged the living room and added a small closet next to the front door. A full size door was out of the question, as it would require 3' of clear space for it to open, and I wanted a door that would use as little floor space in front of it as possible. A pair of sliding doors would not open wide enough, and a single bi-hold door still required too much space for the furniture I have in mind that will go in front of the closet. The answer was a 4 panel bi-fold door - it would only protrude into the space in front of it by a foot or less.
Unfortunately, the selection of bi-fold doors available commercially either aren't available as a 4 panel door in that size, or simply look horrendous. Fine for a bedroom, but this was our living room, so I decided it was an opportunity to make my own frame and panel bi-fold doors. Part of the construction techniques for those panels include wedged through tenons, which I thought I would document here for anyone else who might benefit from my adventures.
For these door panels, I wanted a joint that was strong - this is a door that will see frequent use, and have odd, twisting stresses put on it. I had already decided upon using a frame and panel construction for aesthetic reasons, and for that style of construction a mortise and tenon is entirely appropriate. While a shorter mortise would work, I thought making through-tenons would be fun - along with the fact the fact that I don't have a helper and am short on space as anything. Using a wedged through tenon allows me some slop in the construction of the joint, necessary for how I am to assemble it later. More on that when I get to that part...
First, a couple of graphics to help show some of what I intend to make. First, some of what the terminology I use is referring to:
As you can see, a "haunch" simply refers to where the shoulder is only deep enough to reach the bottom of where the panel slot is cut into the stile. For the record, on a frame and panel door such as this, stiles are the vertical elements, and rails are the horizontal elements. All mortises are cut into the stiles, and tenons are cut on the rails.
Next, a few diagrams showing how a tenon is assembled:
The left side shows a standard wedged tenon, assembled on top, and disassembled on the bottom. The right side shows a haunched tenon, with a disassembled graphic underneath to orient the reader on how it all fits together.
Drilling and Paring Out the Mortises
Since it's a through mortise - and a fairly deep and wide one at that - drilling and paring will work better than chopping the mortise out with a mortise chisel. These are too long and deep for me to do with a chisel with any economy of time, and because they will show, the drill press affords a bit more accuracy in getting them straight through the work piece.
I've already got the channel routed (done on a table saw with a dado blade) for the panels in the stiles to use as a guide for one side, and have marked out the same width for the mortises on the other with a mortise gauge. I true the fence on the drill press to parallel with the drill bit, and drill out the mortise from both ways, choosing a slightly-smaller-than-the-mortise-is-wide brad point bit to do the work, making sure to clamp the piece to the fence to keep it from wandering. Why do it from both sides? Well, first - even drill bits can wander a bit - it's best to drill from each side to keep it as parallel to the outside of the work piece as possible. And second - the drill bits weren't long enough to go through the entire piece anyway....
After drilling, it's time to take a bevel edge chisel after the rough, and open up the mortise a bit:
You can use the holes left by the drill bit as your guide to ensure you are paring the walls of the mortise straight. This work goes pretty quickly with a sharp chisel - the wider the chisel you can use, the better. One that can take a mallet helps too - the goal of this first task is to remove as much of the waste as quickly as I can.
When most of the waste that I can safely remove with a mallet and chisel is removed, I continue paring by hand, keeping an eye on the sides of the holes left by the drill bits:
Notice that I've damaged the edge of the channel, there - right below the ferrule on the rasp that's sitting on the bench. This is OK here, as it's not visible when the piece is assembled - but I should be a bit more careful as I go along.
I don't get it to "finished" depth - not yet, anyway. I'll use the actual tenon that's destined for this hole, so I can fit each one individually. But I do want to get it close, and evenly done, so I continue paring until I'm satisfied it's as good as I can do with a chisel. Then, I square up the ends of the mortise with the proper width chisel:
And finish the squaring up the ends with a large file:
The chisels can leave a pretty rough surface behind, so I level it off with a pattern makers' rasp. These are great rasps because they are at once thin enough to fit into the mortise, and fine enough to leave a fair surface. However I do need to be careful that I'm using a straight stroke when using this method - its easy to round off the corners of the hole.
Work to the marks left by the mortise gauge and the channel for the panel on the other side, and don't go past... Going past will leave gaps that will have to be filled later, and the less gaps, the better. At this stage, it's best to get it so its just a bit shy of where it needs to be. I usually keep a scrap of wood handy that's just a hair thinner than the tenons I'm going to be fitting, and use that to "gauge" how I'm doing - whether I'm keeping it straight, where more needs to come off, that sort of thing. Just a hair thinner, because I like to do the final fitting with the tenon that will actually be used.
Before I had these particular rasps, I used coarse wood files (not rasps) to accomplish the same task - actually the same one as shown in the photo above where I'm squaring up the corner with a file. These rasps work faster, but both will function adequately for the task if you haven't had the money to acquire the more expensive rasps.
Also, it's worth noting that you only need a "perfect" fit where the tenon will be seen - its not that important that it fit perfectly all the way through, so concentrate your best skills where they will be seen.