expansion/contraction in dining chair without upholstered seat

[Jon Crowley]

I have a question that deals with wood movement...

The love of my life would like vaguely mission styled dining chairs. This is a design she likes: http://www.crateandbarrel.com/family...=14229&f=31373

The catch is she wants a solid wood seat, and not a cushion. Generally this style has supports/aprons connecting the four legs, then diagonal braces tie to those to support the seat/cushion assembly.

I see three options for a solid seat:

1- Inset the wood seat just like a cushion. This is bad as it will expand, and drive the apron tenons right out of the mortises.

2- Sit the seat on top of the aprons and notch for the back legs. This will have the same problem, but only for the back apron. Leaving a gap for expansion would fix the problem, but look ugly. I'm guessing the Crate and Barrel example above uses this method, but has flat a plywood seat so movement isn't an issue... ick.

3- Seat on top of aprons, but don't have it overlap the back apron. I'm having trouble visualizing a way to do this without it looking awful. There's an example of that here: http://grizzly.com/outlet/Dining-Chair-Plans/H6562 but something about that just doesn't look good to me.

Am I missing an option here? Some kind of Maloof-esque joint directly connecting the leg to the seat would work I guess, but that would completely change the look.

[Jamie Buxton]

I'm for option 2, with a visible gap. I don't see anything wrong with a gap. It wouldn't have to be very big; the seat is only 18" wide or so.


If you really can't stand looking at the gap, you can hide it. You notch the inside face of the leg an eighth or so, for exactly the height of the seat. The expansion happens in that notch. The only place you can see the gap is by looking at the chair from the back. Heck, you could extend the rear of the seat backwards a bit, so it wraps around to hide the gap from the back too.

[Jamie Buxton]

Here's a sketch of that idea. We're looking at the back of the chair. The dark brown thing is the post. The light brown object is the seat. So you can see the joint, I've pulled the seat out from its eventual position. It would actually sit a little to the left, but not quite so far that the notch in the seat fits firmly into the notch in the post. Instead, there is a gap in there, which is where the seat's expansion and contraction is. You can't see it.

The only trick I can see to this seat is that it must be inserted before you glue up the whole chair. In contrast, a seat without this interlocking notching could be dropped on to the chair after everything else is glued up.

[Jon Crowley]

Thanks Jamie! That's an excellent idea and visual... just what I was looking for!

I'm thinking I'll make the prototype with the visible gap and see how I feel about it. While the notches would hide everything, I'm not sure if it's worth the price of not being able to remove the seat for repairs. Having the seat removable would also allow retrofitting for a cushion if we decide to do that a few years down the road.

[Jamie Buxton]

One more thought...

Run the seat's grain side-to-side. Like you, my instinct is to run it front-to-back. But I can't see any reason to not run it side to side. You nail the seat firmly at the rear, where there's joinery, and let the expansion happen at the front, where there's just an overhang.

There is historical precedent for this. I've seen traditional Windsor chairs with the seat grain running side-to-side.

[Jon Crowley]

The only other reason I can think of for the "standard" grain orientation is it may have made it easier to scoop out a contoured seat.

[Jamie Buxton]

The only other reason I can think of for the "standard" grain orientation is it may have made it easier to scoop out a contoured seat.

Mmm... weak argument, but I don't have a better one.

(But if you're going to scoop out the seats, my favorite tool for that is the Arbortech Industrial. http://www.arbortech.com.au/view/woo...20070412135335 Arbortech says you must use the shield, but it only gets in the way. The thing removes great quantities of wood very quickly. I can rough out a seat in ten minutes or so, then move to sanding discs on the same angle grinder, starting with 100 grit.)