tenons looser than your morals

[estimated reading time 8 minutes]

everyone’s heard of the festool domino. i think it’s an awesome tool but i don’t own one. i’ve used it and it’s fantastic and in my new shop, i expect it will be one of the first things i acquire — though when i will be able to build my new shop is a rather painful question as borders are still closed because of a combination of western idiocy and infectious stupidity. that completely aside, though, most people don’t have a domino and the investment of about a grand for the little one, which i don’t think is worth it as the larger one is only 50% more, is beyond their recreational budgets. that’s ok. and, of course, some people are much more comfortable in the traditional realm of handtools.

you’re in luck, though. loose-tenon joinery is extremely traditional. and it’s easy to make in a handtool-only shop. wait, you thought it was an effect of the modern age on woodworking, didn’t you? no, what’s old is new again. pocketholes aren’t a kreg thing — they’ve been used for centuries. loose-tenon joinery shows up on work as far back as the tang dynasty and probably earlier, though things before the seventh century made of wood are … rare so it’s difficult to get anything like a reasonable sample. i’m not going to tell you to use pocketholes. i hate them. but not for the reason you might think — i hate metal fasteners. just cause i’m a modernist you expected i’d be all for screwing everything that moves, right? well, i’m asexual, too, so i try not to allow screwing in any part of my life. but i avoid metal things simply because i’ve had such awful experiences with hardware in the past and it’s never necessary for fastening. yes, i use metal hinges, though i do tend to prefer making wooden ones when i have time because they look so fucking cool. a tangent, though. a long one. use screws if you like — they’re definitely traditional but i make the very-conscious choice always to find another way. while we’re on the subject, though, i love wooden bolts. drill a hole, make a bolt, twist it in and you have a serious connection. i’ve made many meters of threaded-rod from dowels and i even used wooden bolts for my first knock-down bench. mechanical joints aren’t my issue. i just hate mixing metal with my fine-woodworking.

but we’re talking about wood-on-wood action here. mortises and tenons and … extra mortises? so let’s start at the beginning. what’s a loose-tenon joint?

the simple answer is it’s two holes and a stick. let’s say you want to attach two boards together. the simplest way is to use a butt-joint. no, that’s not when you sit on them and they don’t move cause you’re fat. it’s when you have them “butt” against each other and attach them there with whatever — glue is common but ineffective and screws are unsightly and, generally, ineffective. the butt-joint is an awful joint. it’s weak and ugly — two strikes against it in a world where most joints get two plusses. but what if we could fix the butt-joint? well, that’s where the mortise-and-tenon comes in.

what makes the butt-joint ugly isn’t that it’s one piece of wood against another with a perpendicular intersection. it’s that it’s guaranteed to rack because of pressure and it won’t stay tightly-aligned. a mortise-and-tenon looks like a freshly-made butt-joint but it stays that way. you cut a shallow hole in one piece and trim the end of the other so it has a protruding stick that fits in the hole then, once you apply the glue, they’re firmly-attached with plenty of strong face-grain gluing surface to prevent separation in the future. this joint with its strong bond and mechanical advantages (shoulders, dude — they’re epic) is the fundamental connection method for the vast majority of western traditional furniture. they work for everything from case-pieces to workbenches and they rarely fail.

of course, mortise-and-tenon joinery has a few downsides but none of them are in strength or function. they’re all in complexity of construction and that’s why many hobbyist-woodworkers fear them. they’re not difficult to cut but they can be a bit tedious. and they can be imprecise in ways that show and that’s never a good look. you have to cut the tenon in the end of the board. which means the board has to be longer in both directions — longer enough to accommodate the tenons on each end. but the shoulder-to-shoulder distances have to be exactly the size of the opening the board is meant to fill. and that, if you’re not accurate the first time, can be a nightmare. you can’t just trim the board after the fact and fit it in. you have to get it right at an early stage or start over.

a loose-tenon joint, though, gives far more flexibility.

there’s one other disadvantage to traditional (integral) mortise-and-tenon joints, though. they’re brutally difficult to conceptualize for non-perpendicular joints. if you’re building pieces that come together at an angle that’s not 90-degree, you’d better get your thinking-cap glued to your noggin and break out your drafting tools or you’re going to end up with a sloppy result. i’ve tried to do that on-the-fly before and it never ends well.

in this case, too, the loose-tenon can save you.

a loose-tenon joint is like a mortise-and-tenon except, instead of having the tenon on one piece and the mortise on the other, you cut two mortises on the opposing faces (perpendicular to the plane where the two meet) then use a separate piece as the tenon that sticks into both sides. if this is hard to picture, i’ll make a little diagram but here’s a cute image to remember it. you remember seeing “lady and the tramp” when you were a kid? yes, the disney movie. if you haven’t watched it, go watch it. it’s ok. i’ll wait. it’s worth seeing even as an adult. it’s a great little story about not judging people by their socioeconomic status and the betrayal of unexpected yet proximate evil — i know — pretty heavy for a children’s movie. but there’s a memorable scene where the two title characters (dogs, in case you’re curious) are sharing a romantic, candlelit pasta dinner in an italian restaurant and they somehow both end up trying to eat the same noodle at the same time. as they continue to eat the noodle, they get closer and closer until their lips touch. and this is where we get to the woodworking imagery. the noodle is the loose-tenon. their mouths are the two mortises. got that? a joint as traditionally-european as italian pasta. who’s going to argue with that one?

now we know what it’s for, though, there are two questions that always come to mind — is it strong enough and isn’t it twice the work for a handtool woodworker?

the answer to the first is surprisingly simple. yes. it’s strong enough. actually, because of the large surface-area connection of the glue, assuming you’re using pva (which is strong as all fuck) or epoxy (which could hold the universe together even applied sparingly), the joint is far more likely to fail from the wood cracking than the glue breaking. so the question isn’t whether the loose-tenon is strong enough for your application. it’s whether a tenon is strong enough for your application at all. there are very few places a tenon isn’t enough. and in most of those the answer isn’t to switch joinery methods. it’s to use a bigger tenon or use multiple tenons. in the case of a large panel, for example, you might not want a huge single-tenon. you might want multiple tenons the entire width of the panel — and those being integral or loose doesn’t change the equation in the slightest.

we are used to thinking of loose-tenon joinery as domino-focused and that means they’re usually rather tiny — a standard (the largest the smaller domino can cut) 10mm tenon is only 24mm wide and that’s miniscule, though stronger than you might think. even the large 14mm tenons are only 28mm wide and that’s plenty large but not exactly massive. but if you’re cutting them by hand and preparing and using your own stock you can make a floating-tenon that looks more like an offcut from a piece of construction lumber if that’s what you need for your application. you likely won’t need anything nearly that big but it’s always an option if it feels necessary in the moment.

the other question is about time. and the simple answer is no. in many cases, loose-tenon joinery is actually faster to cut than integral-tenon joinery for one simple reason — you only have to shape the tenon once for your whole project but if you’re cutting them on each part separately you have to shape them independently, one-at-a-time. and that is a huge amount of time. plus, fitting becomes far easier if you’re using a loose-tenon because you don’t have to hold the parts together to check for accuracy — you can just use your loose-tenon stock, which is almost always much smaller and lighter than the mating piece.

so how do you make this wonder-joint a reality? there are two ways and either works but you can realistically take your pick. both work and both are quite strong. one uses a drill (powered or hand-powered, as you prefer) while the other needs nothing but your saw, chisel and, perhaps, plane.

the drill-focused approach is the fastest but the more conceptually-difficult so we’ll start with that one. i think the best way to do this is to start by cutting a mortise. let’s say you want to have a mortise 30mm wide and 12mm tall. perfect. put a 12mm bit in your drill and drill two holes inline on the board with their centers 18mm apart. if you measure from the edges of the resulting holes, you’ll have 30mm. there are many ways you can figure this out. i think the best way is just to draw the mortise you want then fit the bit against the lines but you can do it however you like. anyway, once you have those holes drilled to the depth you want the mortise to go (remember, this is half the total tenon length because the other half will stick that far into the mating piece so don’t go too deep!), you can take out your chisel and turn your two holes into a rounded-rectangle. just connect the lines and you’ll quickly end up with a shape that looks rather similar to a domino’s mortise. cut identical mortises in the mating faces and all other parts you want to join.

now figure out the total length you need for your tenon stock. if you want them to be 50mm deep (25mm on each side) and you have ten joints to make, you need 500mm of tenon stock. make more than that. you’ll lose some for saw kerfs and there’s always a reason to have a little extra. i’d go with a meter or more — in fact, i always try to have plenty of this stuff made up in advance so i can just batch-cut the mortises and know i don’t have to screw around with making tenons to fit in them. get your tenon roughly-surfaced on four sides then take it to your vise and plane the corners round. you don’t have to do this to little pieces — do it to your entire tenon all at once. check it every few passes when you think you’re getting close to make sure you have a nice fit. it should require pressure but nothing that makes you think you’re going to crack the board to get it to seat fully in the mortise. when it fits the mortise, cut each tenon to length and apply glue and clamps and your piece is together.

the other approach is a little slower but far simpler. for that same 30mm x 12mm mortise, lay it out. chop it the same way you would a traditional mortise — use a chisel. don’t worry if the sides are a little imperfect or the bottom isn’t even. nobody will ever see it. all you need is glue-contact surfaces. make your tenon-stock the same way but now you’ve got square mortises so you don’t have to plane the edges round. i know this sounds simpler but simpler doesn’t always mean faster. cutting a mortise with a drill is generally many times faster than doing it with a chisel so you can try both methods and see which you prefer — i like the drill approach and these tenons are hidden so whichever you pick is your secret unless someone actually cuts the furniture apart to figure things out cause it’s glued in there and nothing’s pulling it apart any time soon. fit, cut the pieces apart from your long, prepared tenon-stock and assemble.

this also has the advantage of, when the pieces come together at an angle that’s not 90-degree, simply being a case of cutting the mortises perpendicular to the mating faces, not to the main direction of the pieces, which is the natural tendency. so on a box, for example, where the sides are mitered, you can have 45-degree joints. cutting integral tenons on those is a nightmare. but floating tenons are easy — perpendicular to the mating face means you just drill and chop a mortise as if that 45-degree angle was the surface of the board (don’t go too deep) and slip in your loose-tenon. all the strength of standard mortise-and-tenon joinery with none of the mathematical headaches of complex angles or angled paring-blocks.

of course, there are many reasons to love the standard mortise-and-tenon joint. and this isn’t a replacement for it — and it wasn’t meant to be. but it’s a simple way to get the same functional joint with far less time, effort and potential complexity. and it’s handtool-friendly in a way i think many people have never noticed. hopefully this will be helpful and save some time on your next project! thanks for reading.

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thank you for reading. your eyes have done me a great honor today.