Through mortise and tenons are a popular style of Arts and Crafts joinery, regularly seen in Morris chairs, sideboards, and various case pieces. In this post I’ll show the version I used in my footstool, which can easily be adapted to the mentioned furniture. As with all of my technique posts, I’ll primarily focus on the process. Mentioning my favorite step-by-step techniques along the way; my hope is that you will choose the step-by-step techniques that make sense for you. The goal of this process is to produce a through mortise and tennon that is tight, and has crisp (i.e.: not rounded over) mortised shoulders.Before we get started, a word about milling your stock. When you mill up your mortise boards, leave it a 1/16″ – 1/8″ thicker than necessary. This will allow you extra material to mill off the show-face if you experience any tear-out while cutting the mortise, or rounding-over of the edges while test-fitting your tenon. The tenon board shown on my footstool is 2″ wide and ” thick. The length will be determined by the furniture you’ve designed. The proud portion of the tenon is ” long. Here’s the process I used for this joint:
1. Layout mortise
2. Establish a shoulder
3. Remove waist
4. Square up inside walls
5. Layout tenon
6. Cut tenon–a bit over sized
7. Fit & troubleshoot the tenon
8. Bevel ends
9. Drill pin hole
On the surface it seems like a lot of steps-perhaps a lot of unnecessary steps. But this would depend on the technique you’re using. And a hand cut mortise versus a mortise cut with a hollow-chisel mortiser provides a good example. If you’re using a hollow-chisel mortiser steps 1 is accomplished by simply laying out two vertical lines to indicate your stops, and setting the mortise fence to the appropriate depth. Assuming your mortiser is set up correctly with the bit parallel to the fence, Step 2 is not necessary, and steps 3 and 4 are performed simultaneously by the mortiser.
Now, if you’re cutting the mortise by hand, the first four steps become a bit more drawn out. Laying out the mortise as shown in photo 3 is largely unnecessary, unless you need a visual reminder of what you’re removing. Otherwise you can move right to laying out the mortise using a marking guage (photo 4) and Xacto knife (photo 5)
Photos 6 and 7 show the tools and results of establishing the mortises shoulder. This is a great example of a principle step-one that you usually don’t explicitly perform, but if you don’t understand the principle, you’ll have all sorts of problems fitting your tenon. Establishing an accurate shoulder ensures that your mortise exits the back-face of the board at the same point it enter the front-face. When using a mortiser to cut your tenons this step is implicitly performed by the mortiser–assuming your chisel is set up parallel to it’s fence. But when cutting the mortise by hand, this is one of the steps you can take to ensure the mortise goes through the board at the appropriate angle. Router cut mortises also negate this step.
Once the shoulder is established, you’re ready to remove the waste. A drill press (photo 8), mortising chisel, or router can all be used to perform this step. If using a drill press you’ll then use a bench or paring chisel referenced on the shoulder to trim the sides perpendicular to the board face (photo 9). There is another method you could use to ensure the mortise walls are perpendicular to the board face. That is by laying out the mortises, and removing waste from both faces of the board. Thus if there is any inaccuracy in your walls being perpendicular, the error would be in the middle of the board. This method is best used when cutting through mortise is thick boards, such as a 1 ” x 1 ” leg post.
Finally, photo 10 and 11 show a couple ways to confirm your mortise walls are perpendicular. You can use a combination square registered on the layout face of the board, and you can use your marking tool, with its original layout setting, to confirm your mortise is exiting the board in the same location as it entered.
Next let’s talk about the tenon. The key to a tight fitting through-tenon is this-sneak up on the final size. That is, initially, cut the tenon too big for the mortise, than sneak up on the final snug fit. When it comes to tenons, I’m traditionally a tablesaw tenon maker. For me, it’s the fastest to set up and execute. So photos 12 and 13 show the layout and cutting of the tenon.
Once I’ve got the initial tenon cut, I start sneaking up on the final fit. That is removing a small amount of the tenon face surface until it fits the mortise. You can see in photo 14 a couple different ways to do this. Whether using a shoulder plane, pattern makers rasp, or plane makers float, the key is to remove an equal amount of materials across the face, and from each side. Until you can do this by sense or feel, it’s best to draw a pencil-line matrix on the face to gauge how evenly you’re removing material. When you think you’ve got the right size, gently test fit the tenon in the mortise on the front-face of the board-this is the side you laided out the mortise on(photo 15). Do this gently. If you’re too aggressive you can roll over the edges of the mortise, and you won’t have a crisp looking joint between the mortise and tenon. However, if you do manage to roll over the mortise edge, and you milled the mortise board a little extra thick, you can just plane it down to restore a crisp edge.
Another technique you can use if you’re having difficulty fitting the tenon, is to apply a very slight back bevel. This effectively increases the mortise size on the face that the teonon shoulder will sit against. Photo 16 shows the back-beveling being cut; with the front-face of the mortised board facing up, lay your chisel against the wall of the mortise, with the edge about half way down the wall. Then tilt the chisel slightly away from you and pare off a small shaving. Continue with this technique around the whole mortise. Once you’ve got the tenon fitted (photo 17), draw a line around the tenon where it intersects the mortised board. This line will act as the base line for beveling the end of the through tenon. Remember as you bevel the tenon, that the pencil line is on the proud side of the mortised board, so the bevel area should include the bulk of the pencil line.
Photos 18 and 19 show a couple different ways to bevel the tenon end. I’m applying a 45 bevel to all four sides. The simplest way, for me, is to use my circular sander with a jig. To ensure I don’t sand away too much material, I’ll either simply spin the wheel by hand, or turn the sander on for a second than off and let it coast-down, as I move the teonon into the disc. I sand until the pencil line is all but gone. A sharp low-angle block plane will do the job as well, and almost as fast. I’ll cover this in a future technique post. With the tenon beveled do one more dry fit. It should look something like photo 20.
Finally, with the tenon removed I layout and drill the pin hole in the mortised board. Notice in photo 21 the pieces of scrap wood wedged in the mortise; these are to prevent tear-out when drilling the pin hole which extends through the mortise and approx “- ” into the opposite edge of the mortised board. Once your piece of furniture is assembled, you will use the pin hole in the mortise as a guide to drill through the tenon, and install the pin. Finally, follow the links below to a few good references on cutting through mortise and tenon joints, as well as information on designing and installing wedged through mortise and tenons. REFERENCES
- Gregory Paolini-A portable Book Rack; Fine Woodworking #197; Covers template and router cut through mortises (online demo)
- Woodworking Magazine-3 Methods to Making Through -Mortises; Winter 2008; Covers types of mortises, hand-cut mortises, router-cut mortises, and hollow-chisel mortiser cut mortises.
- The Complete Illustrated Guide to Joinery by Gary Rogowski; Taunton Press; Pg 145 – 149; Covers through mortises with router and template, through tenons with a plune router, loose wedged through mortise and tenon, and making loose wedges.