Mortise and Tenon
Before we start on our table, we need to take the time to make a few practice joints. The oldest and strongest joint out there is the mortise and tenon. It’s also the only joint used in this occasional table.
I wanted to make a set of bents to show you this but the hickory I had on hand developed quite a few cracks that kind of killed that idea for this weekend (a total drag for me because I really wanted an excuse to make the bents). On the other hand it’s good that I could not do that because it may force you to take a look around your shop to see what you need that may require mortise and tenon joinery (workbench, bents, a drafting square for drawing…something that you can evaluate)
Failing that…a practice piece is a good warm up.
We will start with a piece of easy working wood (pine, poplar, alder…anything soft). Your dimensions should be in the realm of 3/4”, 2”, 24” (keep in mind the exact measurements are not important, just get close while removing the lease amount of wood to get square stock). Flatten a face, checking for twist, bow, and cup (this will be your true face…mark it with a squiggly), square an edge to it (true edge, mark it as such), plane to width and then plane to depth.
Let’s also cut the then ends off square so we can show you how to make accurate (and visually appealing) saw-cuts at the bench.
To cut the end of your board square, use a knife and a square to make a mark square all the way around the edge of your board (referencing the stock of your tool on you “true” face and edge…if it sounds like I have repeated that a lot it’s because it’s one of the most important things you can do to create decent handwork)
Use a wide chisel to deepen that line (wide chisels are easier to steer) and then make another cut on the waste side to create a “v”. This “v” guides the saw and creates a cleaner cut since the outside of the work has been cut with a chisel instead of a saw…this is one way you can get away with a rip saw on a crosscut.
Occasionally this will result in a saw whisker (yes I know the corners have the “v” notches in them…I did not cut them off on this one since I wanted to focus on the joint rather than the saw cuts)
Take this whisker off with a sharp chisel and a light touch.
For the ends of boards that need to be of an accurate length a simple knife line around the board and a notch to start your cut is plenty.
Saw this board in half on and square the ends for practice sake (make sure your have reference marks to denote your true face and edge on what will become your two boards). Today I’ll be making a corner mortice that you would be likely to see in a door, rebated back in a cabinet, or…a table leg and rail.
Make a mark on the true faces as shown so you know how the joint goes together, on a full fledged assembly the mark would not be on the joint (and not it pen), but this simplifies things for this project quite a bit.
On the piece with the point we will make our mortice. To start, make a mark on the inside edge to designate where the bottom of the tenoned piece should fall, this is the only mark you should make…unlike some people.
Use dividers to set the set back distance, this should be about a quarter inch to give strength to then end of the joint while not losing too much glue surface (set these dividers aside since you will need this measurement later). Make an indent with the dividers and extend that indent into a knife line (don’t make these very deep, or stop a bit shy of the edges of the board since a deep score mark could show on the outside of the joint)
Then you can use your marking gauge to locate the sides of the mortice. In a closed mortice I only make one line with my gauge since, the chisel itself defines the other wall. On a through mortice, the extra line is worth the effort since in reduces the chance of tear-out on the show side.
Once you have located the mortice, you can start cutting it out. I always make my first two chopping cuts about an 8th inch away from my scribe lines for the ends of the mortice. Because of the force of the wood on the bevel of the chisel, the tool will not drive straight down so excavating the depth of the mortice first then chopping the ends straight down at the last ensures accuracy (the 8th inch waste wood that you leave till the end also gives you a sacrificial leverage point to pull chips out).
I can also set a square next to my work to ensure I am cutting straight.
Clamp the work to your bench so it cannot move from the force of your chisel. On narrow pieces make sure to arrange your work so it’s supported enough to not fall over.
My procedure for getting a mortise excavated is as follows.
Make two initial cuts about an 8th from the ends, when doing this I tilt the chisel away from the joint a bit so it drives more straight. This cut never goes further than the bevel of the tool (trust me getting a chisel stuck in your work is not entertaining)
Lean on the chisel make light scoring cuts along the length of the mortise (minus the 8th inch on the ends that we will leave until the end). Clean these chips out to create a small (8th or so) trench, this is a great aid in locating the chisel during the “bash out” part of the mortise, and it reduces your chances of tear-out on the side of the joint.
Use the chisel with the bevel towards the higher side of the waste in the mortise and take small bites with the force of you mallet. The chisel will cut chips and because of the bevel will also break them into the empty part of the cut (waste you have already cut). Lift out these chips with the tool. As I get deeper into the cut I take bigger bites as I have past the worry of tear-out. Take care not to let the chisel twist during the process as this will create and over-sized mortise wall.
I make a mark on my chisel to give me an idea of how deep the mortise needs to be. A set of dividers and and combination square is useful to have on hand. Set the dividers to your tenon length and your combo square a bit longer so you can check that your mortise will receive your tenon without the tenon bottoming out. I tend to march back and forth across the mortise with my chisel until I am at depth but there are other ways to get to the same goal (aren’t there always). Double check this carefully to make sure you have reached depth across the entire cut.
Shear off the ends of the mortise and remove those chips careful not to dent the ends of the mortise. Recheck to make sure the depth is consistent and deep enough.
When laying out the tenon you can use the mortise to directly gauge from one piece to the other. Set pieces flat on your bench and set the tenoned piece against the mortised piece so you can access the mortise from the outside. Use a scribing knife to make marks on the tenoned piece using the mortise wall as a guide. Extend these marks to around the outside of the joint. The ideal way to do this is to have a marking gauge set to one wall of your mortise, and another set to the other wall, (this assumes you are marking from the face side each time) these two gauges left untouched could mark all your mortise and tenon joints for an entire project.
You can use the dividers you used earlier to mark the marks for your setback (the smaller waste material section of the tenon) and then extend those lines. You can imagine that it is a good idea to either mark all your pieces in a project in series, or have a ton of layout gear.
To saw out the waste I have tried several different approaches and I am still experimenting. Woodwork is best experienced from multiple perspectives, the more workable methods you try out the more our craft will make sense to you on a whole. For now, let’s saw the tenon cheeks first followed by the setbacks (the cheek is the part of the tenon that will slide into the mortise while the shoulder is the part that stops the work from sliding further into the joint). In the video I removed the cheeks first the cut the shoulders, then do the set-back cheek, main shoulder, then setback shoulders. This give you good viability and good registration surface with the saw. I switch up the order a bit in the video below but you get the idea..play around until you find something that makes sense to you.
For the cheeks I make a simple notch to start my cut, on my shoulders I cut the whole groove with a chisel before I start sawing.
For extra credit you can draw-bore the joint. Use a dowel (or even better whittle a peg to an even diameter) to force the joint tight and make in permanent. I wedge or draw-bore most of my joints because I don’t trust glue, and I like the permanence of it. Draw-boring is also cool because you can create assemblies without clamps. To achieve this affect drill a hole through the mortise piece in what you estimate to be about the middle of the tenon (do not have the joint assembled), it’s a good idea to have scrap in the mortise to prevent tear-out on the inside of the joint. Ice this hole is drilled assemble the joint and use your drill to mark the center of the joint on the tenon (the point on a brad point drill works well for this.). Teak the tenon out and drill a hole slightly more towards the shoulder of the tenon. When assembled the holes are slightly offset and the pin being driven through this hole forces the joint tight and makes and permanent. A few tips, take a pencil sharpener and ease the edges of the pin so it goes in more easily. Also when you are gluing up, make extra pins and put a bit of wax on them, this helps matters tremendously. Use a playing card with a hole in it to saw off the pin without scoring your work and then trim it flush with a chisel, or do the chisel trick as shown in the video (which works better on softwood pins than hardwood ones.)
When you are done you can saw out everything but the joint (saving enough material that you can evaluate or even mark your mistakes) this way you can continue making practice mortices while only using a few inches of the wood each time. Practice makes perfect, applied practice teaches you more quickly…find something.
-- Make furniture that lasts as long as the tree - Ryan