Thursday I resumed work on my 2nd version of Curtis Buchanan’s democratic chair. The first piece of furniture I assembled this year was my initial attempt at this chair back in January. https://pfollansbee.wordpress.com/2020/01/06/finished-my-curtis-buchanan-chair/
For my first Windsor-style chair in decades, I was happy enough with that one. Which is different from “I was happy with it.” One problem I had was the legs splitting at the joints.
I suspected my tenons were too large. I talked to Curtis about it, and if I remember right, he said because of the steep angle (say where the side stretcher meets the leg) you can get splitting. Suggested yes, make the tenons a bit smaller than I might in a ladderback chair. I was using white ash. I think another factor was the auger bit I used. It has a thick lead screw that might have contributed to the splitting.
For me, one of the most glaring problems was boring the mortises directly in the tangential plane of the legs. And the orientation of the leg is dictated by the orientation of the seat. In this case:
- the long fibers (the “grain”) of the seat run front-to-back.
- The growth rings in the legs’ tenons (the whole leg actually) are therefore oriented so they run perpendicular to the fibers in the seat.
- The leg is split so the wedge is also perpendicular to the fibers of the seat.
This makes the front view of the front legs (and back legs) the tangential plane. And it means when boring the mortises for the side stretchers you’re boring directly into the growth ring plane. Where ring porous woods split very easily.
BUT – I hate looking at the tangential plane of ring porous hardwoods like oak, ash, etc. And on my first democratic chair, the front of the front legs (and back of the back legs) is this plane.
I thought about switching the leg orientation 90 degrees to the “usual” format. Then you wedge it just the same. This puts the leg’s radial plane, which changes less than the tangential plane, running in the direction in which the seat moves the most from one season to the next. So in a worst-case scenario the seat could split I guess, if it shrank a lot versus the leg tenon which wouldn’t shrink much. I think if you use a softwood seat like white pine, and hardwood legs, the seat will compress before it will split from the legs. I bet any problem would be at assembly, not afterwards. I could, of course, be wrong. It’s been a long time since I was really a chairmaker of this sort.
In the usual orientation, the leg’s radial plane lines up with the long fibers of the seat. The seat does not shrink in this direction at all; maybe the tiniest fraction of an inch. If you were to make the change I was thinking about, the radial face would now be the front view of the legs. Better visually for me, but now you’d still be boring into the radial face./growth ring plane, where ring porous hardwoods also split very easily.
In the ladderbacks I learned from John Alexander and Drew Langsner, we positioned the posts’ growth rings at an angle to the rungs…they coined the phrase “post and rung compromise.” They didn’t make up the concept, it came from studying old chairs. The reason for it is to reduce the chance of splitting the legs when driving the rungs in – the mortises are bored between the growth ring plane and the radial plane. Below is one of Chester Cornett’s chairs, showing the front post oriented with this post & rung compromise. The radial crack bisects the angle between the front & side rungs. But you see how neither of those mortises are in the radial or growth ring plane. Some of Chester’s chairs that I saw used sassafrass posts, this one was white oak, very slowly grown.
I decided to try something this on my democratic chair #2. I was moderately successful. The legs & stretchers on this chair are also white ash, and had grown a bit too slow for this application. Too many growth rings make them a bit weak. I oriented the stretchers in the usual way – their hardwood-to-hardwood mortise & tenon joints seemed more critical to me than the hardwood/softwood leg-to-seat joints. So the growth rings on the side stretchers are parallel to the floor – those on the center stretcher are perpendicular to the floor. This means the mortises for the center stretcher are bored into the radial face, directly in the growth ring plane.
One side stretcher cracked slightly like on the first chair. I keep learning.
But it was the legs that I moved around. I re-positioned them just a bit, turning them in their tapered mortises so the growth rings were angled to the fibers in the seat. The wedge, and the wedging action, are still perpendicular to the long fibers in the seat.
This way I was boring the mortises for the side stretchers one facet off from the growth ring or radial plane.
It worked pretty well, one leg has a small split, but that might be more due to the slow growth rings than anything else. Next time, I’d choose a faster-growing log, and I might turn the tenons rather than spoke-shaving them. It’s better than first time out, almost to where I’m happy with it.