Wood chair: Cutting out back post vs (domino) tenons

Question

I would like to build several outdoor teak chairs, similar to this one https://www.williams-sonoma.com/products/larnaca-outdoor-dining-side-chair/?pkey=s~larnaca~70&sbkey=williams-sonoma-home

What I am wondering about though is, if I have to cut out the rear leg/back post for the angle or if I could use a (domino) tenon. A tenon would not only be easier but also save a lot of wood. All chair-building plans I found so far seem to cut out the rear leg rather than use a tenon joint between the back post and rear leg. Would a tenon joint not be strong enough?

Answer 1

What I am wondering about though is, if I have to cut out the rear leg/back post for the angle or if I could use a (domino) tenon.

Those back joints take a lot of stress! Not only do they carry a lot of the weight of the person sitting in the chair, they also have to resist racking in two directions and the force of someone leaning on the chair's back. It's even worse if the person tilts the chair back on it's back legs.

There are chair designs where the back leg and the posts holding the chair back are separate pieces, but in those cases the back usually has other support, like vertical spindles or the arms of the chair. Even with those extra supports, the joint between the posts and (typically) the seat often fails.

Chairmaking and Design is a great book on chair design by Jeff Miller, and one of the lessons I took from it is that there are lots of different possible designs for chairs, and also lots of problems that only become apparent when you build a prototype. In that spirit, if you think you can do something differently or better but aren't sure that it'll work, then by all means build one and see how it goes. In this case, you don't really have to build the whole chair; you could just cut out one solid leg and also build a version joined with tenons or floating tenons and test them. Keep in mind that there are already two mortise and tenon joints where the seat rails connect to the back leg, so fitting another one in the same area without losing too much strength could prove difficult.

If you're not interested in doing some preliminary testing, I'd stick with using a single solid piece. You can of course reduce waste by nesting several legs together. Paying extra for a wide board could make sense because you'll reduce waste.

Answer 2

For a two-piece leg I was all set to recommend alternatives to typical/usual Dominos¹ for reinforcing the joint so as to make them a more viable option, until I realised that the area immediately adjacent to the joint needs to accept the horizontal tenon/dowels/screws that would join the chair rails to those legs.

Any such fixing either A) directly interferes with a Domino (or other floating tenon) regardless of length, ditto dowels, that lies vertically in the wood there or, B) undermines the wood to both sides compromising strength. My gut feeling is there's simply not enough thickness here — even assuming it's strong, straight-grained wood you have bought — to get a guaranteed result². Sure, joints like this are seen in modern furniture but that's no recommendation; numerous times I've seen furniture repairs where joints featuring just such intersecting or crossing/adjacent joinery have failed, apparently spectacularly judging by the level of splintering around the joint.

With the potential for waste and that you want to use teak I can fully understand the desire not to have to make the rear legs by cutting out of the solid (and that's even without the inflated prices we're seeing today). However, I think the above makes making these legs from two parts really untenable, not if you want to ensure a long and safe working life.

If you can't swallow the cost of teak in the required dimensions to make the legs from the solid I have two suggestions.

Laminate
Obviously there's still a certain amount of waste to live with here, but you start with thinner stock which won't have the same $$$ attached to it.

Choose a different hardwood
I think perhaps the best option here is to choose to make the chairs from another hardwood (and not just because it will be more modestly priced).

There are actually numerous domestic hardwoods you could pick from that have superior exterior durability. That could probably do with being stressed: superior durability to teak³.

Even white oak potentially offers a very viable alternative, and while it might be more expensive currently than one would prefer it won't be in the *gulp* territory of teak.

If oak doesn't take your fancy see table from the FPL in this previous Answer.

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¹ Which are too short to rely on.

² Which isn't something you can guarantee you'll be able to get going in to the project. Very often with tropicals unless you're paying a super premium or can carefully select in person from a large standing stock at the supplier (best of luck with that!) you're getting stuff that is not ideal.... and might even have been discounted by a previous generation of woodworkers.

³ Because you won't be buying old-growth teak.