Cutting Mortises 17th-century Style (That is, by Hand)

The following is excerpted from Chapter 4 of “Make a Joint Stool from a Tree,” by Jennie Alexander and Peter Follansbee.

Joint stools are a fascinating piece of British and early American furniture. Made from riven – not sawn – oak, their legs are typically turned and angled. The aprons and stretchers are joined to the legs using drawbored mortise-and-tenon joints, no glue. And the seat is pegged to the frame below. Because of these characteristics, the stools are an excellent introduction to the following skills.

• Selecting the right tools: Many of the tools of the 17th century are similar to modern hand tools – you just need fewer of them. “Make a Joint Stool from a Tree” introduces you to the very basic kit you need to begin.

• Processing green oak: Split an oak using simple tools, rive the bolts into usable stock and dry it to a workable moisture content.

• Joinery and mouldings: Learn to cut mortises and tenons by hand, including the tricks to ensure a tight fit at the shoulder of the joint. Make mouldings using shop-made scratch stocks – no moulding planes required.

• Turning: Though some joint stools were decorated with simple chamfers and chisel-cut details, many were turned. Learn the handful of tools and moves you need to turn period-appropriate details.

• Drawboring: Joint stools are surprisingly durable articles of furniture. Why? The drawbored mortise-and-tenon joint. This mechanical joint is rarely used in contemporary furniture. Alexander and Follansbee lift the veil on this technique and demonstrate the steps to ensure your joint stool will last 400 years or so.

• Finishing: Many joint stools were finished originally with paint. You can make your own using pigments and linseed oil. The right finish adds a translucent glow that no gallon of latex can ever provide.

Now we can return to the framing parts, starting with the stiles. The first step is to lay out the mortises. We’ll outline these steps one at a time because it can get confusing. We will call the mortises for the front and rear rails “straight” mortises, those for the canted ends of the stool we will call “angled” mortises.

Stack the four stiles together, with their beveled inside corners touching, and with radial faces up.

These radial faces become the “front” and “back” faces of the stool. Take one stile, and work on its radial face.

To lay out the stiles’ square blocks and the straight mortises, it’s easier to use what a carpenter now calls a “story stick” that is marked with the stiles’ details, rather than working from paper drawings or patterns. This shop-made stick records the markings that are then transferred to the stile. We have made these sticks to record different stools. The locations and heights of the squared blocks, turning details and positions of mortises can all be taken from the stick to the stile. It is best to mark ONE stile from the stick, then the other three stiles from that first stile.

Make sure the foot of the stile is trimmed square. Line up the foot of the story stick and the feet of the stile. With an awl, mark the limits of the square blocks and scribe these marks across all four faces of the stile, with one exception – the top of the stile is marked only on the radial face and the corresponding inside tangential face (where the straight apron mortise is located).

Now line the stick up on the inside face and mark the locations of the mortises on this tangential face.

One thing to keep in mind is that the top of the apron mortise is not at the same height as the top of the stile. This mortise drops down about 3/4″ from the stile’s top end. Eyeball the top of the apron mortise and scribe it with the awl and square.

The next step is to mark the mortises with the mortise gauge. To set the gauge, make a mark with your chisel’s edge perpendicular to, but right against the stile’s arris. Next, move over one chisel width and bear down hard enough to make a mark in the wood. Then set the pins of your mortise gauge according to the location of this second chisel mark. The result is a mortise that is set in from the face of the stock the thickness of the chisel. Our mortises are usually 5/16″, set in from the face 5/16″. This spacing is based on studies of period work; 5/16″ is almost a standard from what we have seen.

The Angled Mortises
To find the location for the angled side mortises, use an adjustable bevel set to the desired flare angle. A slope of 1:6 is what we have used on several stools. Our studies of 17th-century stools show flare angles right around that figure, some less, none more. To set the bevel, set a straightedge on a framing square, positioning it at 1″ on one leg, and 6″ on the other. Then adjust the bevel to this angle and lock its nut to secure the setting. You can then scribe this angle on a piece of wood, or even scribe it on the wall. Like the adjustable gauges, the bevel can lose its setting if bumped. Having the angle scribed somewhere makes it easy to reset it. Alexander turned an adjustable bevel into a fixed one by threading a bolt through its stock and blade.

To lay out the side mortises, you must carry the line that designates the top of the stool from the front radial face across the side tangential face. Set the bevel with its handle on the front face of the stile. Line it up with the marked top of the stool, with its angled blade pointing upwards on the other outside face of that stile. Scribe this line with the awl.

Then use a square to carry this line across the other inside face. So the sequence is square, bevel, square. Remember that it’s best to carry the lines across the outside faces; the inside faces are unreliable. This layout is both simple and complicated at the same time. Sometimes it helps to stand the stile up and tilt it as it will be in the finished stool. Then you can easily visualize where the angled mortises are and how they rise up higher than the straight mortises.

You can repeat this process for the top edge of the stretchers’ mortises. Or you can mark this from the story stick, this time lining up the top of the stool with the scribed line that designates the top of the side apron.

Now mark the mortises’ height and width on these faces of the stile. After you mark out two stiles, lay them side by side and check that they agree. A front or rear pair should have their radial faces matching, with the straight mortises aiming at each other, and the side, angled mortises rising up toward the top of the stool.

Mortising
Once you have struck the layout of the mortises, secure the stile on the benchtop near its edge. Shove one end of the stile against the bench hook then secure the stile with the holdfast.

Begin mortising by holding the mortise chisel with the handle tilted away from you, leaving its bevel just about plumb. Position the first cuts with the mortise chisel about in the center of the mortise’s length. A blow from the wooden mallet drives the chisel downward. Turn the chisel around, and make another chop aimed at the first. The result is a V-shaped opening at the middle of the mortise’s length. Alternate the chisel’s position in this way, enlarging the V-shaped cut; the goal is to reach the depth at the center of the mortise as quickly as possible. Then the rest of the work is just cutting down the end grain to lengthen the mortise. As you get to the ends of the mortise, bring the chisel upright so that its back surface is perpendicular to the stile’s surface.

There are a few stances and postures we use that increase the efficiency in mortising. For most of the work the chisel is driven with a mallet, but sometimes hand pressure is useful as well. When using hand pressure, it helps if you rise onto the balls of your feet and come down with your whole body to drive the chisel. Lean on the top of the chisel handle with the front of your shoulder to help drive the tool into the wood. Then you can pry the waste up from the bottom of the mortise. In fig. 4.12, the left hand is used to position the chisel, and the right hand and upper body are driving the tool into the wood.

It is critical to keep the mortise chisel parallel to the face of the stile. You can sight against a square positioned on the benchtop. Drive the chisel into the mortise, then step back and sight it against the blade of the square. With practice you will learn to sight this against the face of the stile, and not need the square.

The moisture content of the oak is important at this stage; usually it’s fairly wet inside when you chop these joints. The stock in the photos was planed wet from the log less than a month before cutting these joints. The straight-grained nature of the riven stock makes mortising easier than ever. The same principles that apply to splitting apply here as well. In effect the chisel is entering the wood directly on either the radial or tangential plane.

Chop the mortise to a depth of about 1-1/2″. It’s easiest to get that depth at the middle of the mortise; at the ends it requires a little more attention. There is a tendency to pry against the end grain of the mortise – this will bruise and deform the wood there. Stay away from the final ends of the mortise at first, that way you can pry against the end grain that will end up as waste. Finish up by taking cuts straight down the end grain with the back of the chisel perpendicular to the stile.

To get the last bits out at the bottom of the mortise’s ends, chop straight down into the ends, then turn the chisel around, and with the bevel down, drive the chisel into the midst of the mortise, and come toward the ends. Now bring up the chip on the back of the chisel.