Chris Schwarz's Blog

Chair Joinery: Tapered Tenons & Tapered Mortises

Because chairs take abuse like a rented mule, the simple mortise-and-tenon joint is sometimes not enough.

In traditional Windsor chair construction, the legs and spindles are attached to the plank seat using tenons that are cone-shaped along their lengths. So the mortises have to be the same shape. These tapered joints are clever. The more you sit in the chair, the tighter the seat-to-leg joints become.

Making these joints requires some cleverness. For years I used a tapered reamer from England that never worked well. I had borrowed a reamer made by Fred Emhoff and it worked well, but was no fun to sharpen. I’ve also used wooden reamers with a bit of steel embedded in it, which scrapes the sides of the mortise.

All those solutions worked, but none as well as the Veritas Pro Tapered Reamer. For less than $43, it is a great value. I’ve paid more for reamers that didn’t work as well. The blade is removable and easy to sharpen. And – best of all – you can adjust the depth of cut. This is worth more than the price of rubies. With softer woods – pine, poplar and mahogany – you need a deeper cut. This reamer delivers.

I’ve not used the Lee Valley Standard Reamers. They are less expensive, but you cannot adjust your depth of cut and they are more difficult to sharpen like a traditional steel reamer.

On the tenon side of things, I used to turn my tapered tenons on a lathe. That works fine, but it is slower than using a dedicated spoke cutter (unless you are a production turner, of course. I’m not).

The Veritas Tapered Tenon Cutter is, quite simply, the best one I have used (and I’ve used many). I use the 1/2” model – the size is the resulting diameter of the tip of the tenon. The blade is easy to sharpen, like a spokeshave blade. But the best thing about the tool is that it offers registration marks on the body of the tool so you can set the blade to exactly the correct skew. I know that the perfect skew for mahogany, for example, is to set the blade so it’s on the second mark at the opening of the tool and on the third mark at the top.

The body of the tool is heavy, which helps keep it in the cut. The only modification I have been pondering is making a long wooden handle for the tool so it will work more like an old-fashioned auger. After 32 mortises this week, my wrist is a little sore.

These tools aren’t new. I’ve been using them for a couple years. But as I was making a pair of Roorkhee chairs for an upcoming article, I was reminded of just how good they are. If you make traditional chairs, these are highly recommended.

— Christopher Schwarz

6 thoughts on “Chair Joinery: Tapered Tenons & Tapered Mortises

  1. jyane

    When I first thought of tapered mortise and tenon, I pictured joinery similar to those standard rectangular shapes, but wider at the top and narrower at the bottom. Sit on the seat of this chair while the glue is curing.

    I’ve never seen such a joint; have you?

  2. TCBound

    Having been making windsor chairs for years, I know I’m going to be turning the legs, stretchers and stub spindles during the process, so why not just turn the tenons at that time. But, in the case of other chairs using unturned stretchers or posts (Welsh stick chairs, for example), the tenon cutter would be a boon.
    I’ve used traditional spoon bits and tapered reamers and fully agree that the sharpening is problematic, so this reamer with its separate blade would be a way around the cussing and fuming when the “sharpening” job is less than stellar on my spoon type tapered reamer. (I do think my reamer has a sharper angle and much smaller point, though.)
    As to the tenon cutter going off-center; on my chairs over the years, I’ve noticed that the tenons and mortises rarely are a perfect fit, but add the wedges and I have yet to have one come apart…without some serious “help”!

  3. garycruce

    I’ve used the same tenon cutters for several years as well. I agree they need a handle and made one myself, although there isn’t an easy way to attach to the little buggers. I usually clamp the tenoner into a vise and hold and turn the leg (like sharpening a big pencil) – I find I can keep the tenon aligned with the axis of the leg easier. Once I have a good start (and my forarms are burning) I switch to turning the tenoner as you showed in your video.

    I use the less expensive reamer from Lee Valley and like it well but my choice of it over the full meal deal you have was driven by my desire to chuck it into my drill press (it has a hex shaft). I know it is not an advise move but frankly I find the macho boring and reaming by eye method of making windsor chairs a bit much for me and prefer the consistency I get out of my home made tilt table on my drill press. I do run the reamer as slow as possible, and feed it slowly, it gets hot quick.

  4. jason.weaver

    Looking at the cutters it seems that the mortise would be cut in the same direction as the tenon — a cone-shaped hole, to receive a cone-shaped piece, but the diagram on Lee Valley’s site almost looks like the mortise is done from the top of the piece so that the tenon can be wedged.

    Am I seeing that right? If so, I assume that you can use them either way – in the same direction for the rails, and coming in from the top for wedged mortises in the seat.

  5. Julian

    Wow, was that trick photography? I was amazed at how cleanly and quickly that spoke cutter worked. I may have to buy me one of those cutters. I’ll add it to my collection of tools that I really don’t need but just want. I hope you post more about the chairs your building.

  6. jlebans

    Reamers are among the arcane religious tools of chairmaking, it seems (a list that includes spoon bits, scorps, travishers, compass planes and all sorts of good stuff). I like the Veritas reamer as well, for the same reasons you point out. But the angle is a bit shallow, and its thick, blunt point means small tapered mortises (like in a Windsor arm) can be a bit tricky. Wooden ones, like Elia Bizzarri sells can have a longer taper, can be sharpened as well, and you can choose any angle you like.

    I found the tenon cutter, however, to have one weakness over turning tenons on the lathe. If you’re not very careful with the tool you can cut the taper off-centre, and thus off-angle. This can ruin a leg, and your whole day.

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