I received this question in episode 4 of the Ask Brian Boggs Show:
“Can Brian explain his technique on glueless chairs, where he hyper-dries rungs and assembles before they swell.” ~ Martin Goebel
If you all don’t know who Martin Goebel is, check out Goebel & Co. Furniture. They do some really interesting stuff up there in St. Louis, Missouri.
I got my start building greenwood chairs and learned this technique basically through John Alexander’s book, Make a Chair from a Tree. The idea of a greenwood chair is that you are taking a log apart and putting it back together using the tree’s movement of moisture properties and the way wood behaves to actually hold the piece together, rather than using adhesives to hold it together.
One of the things that has been great about that as my beginning is that it has really thoroughly shown me the way wood behaves. When you’re splitting wood out by hand like I was at the time, it was real easy to physically get a feel for the material and seeing the fibers separate gave me an understanding that I don’t think can be had in another way. So that was a really important part of that era and it still feeds just about everything I do in the shop now. But back to how that works, you’re splitting the wood apart and generally working with it green. The greener the better from the standpoint of working with the wood because it’s a lot softer and easy to work then, and it makes the hand tool work a lot faster.
Another thing about riving stock out, which is how I did this certainly in the beginning is that when you’re splitting wood from the log, you’re getting wood whose fibers are completely intact, meaning that that particular stick of wood is as strong a part as that tree has to offer. You go beyond that by selecting the right trees, the right species to best suit the demands that that particular part has, and then you control the drying process for the same reason. You’re wanting to best utilize the wood’s properties and best utilize the wood’s behavior to strengthen the frame that you’re creating. While that level of working with wood’s behavior is unique to greenwood working and greenwood chair making and I know Peter Follansbee does a 17th century joinery that actually uses rectangular parts with this similar thinking in terms of being able to efficiently work with greener wood.
But what we’re doing in making greenwood chairs is the legs are not totally green, but partly dried, and I like about 15% to 18% as an ideal moisture content for the legs at assembly time, or at the time that you’re drilling holes to receive the rungs. The rungs are … there’s a couple of ways to deal with the rungs, but basically at the time that they are the right size and assembled, those rungs should be around 4% moisture content. What happens is that the rungs, you know the rung goes inside the leg and there’s a ring cut around the tenon of the rung that’s inside the leg, and the leg shrinks into that ring and clamps down on the rung and it never comes apart. It really can’t come apart mechanically. It’s a joint that has mechanics that I don’t believe is possible without the deformation of green wood post assembly. And that’s a really unique thing about that.
One of the things that John Alexander did not cover in that book though, is the importance of working with specific species. Well actually, he did talk about that some. He uses hickory for the rungs. But I got to really like soft maple for the legs and the reason is that soft maple’s ability to deform is really great. It not only can deform really well into the notch of that rung, but the behavior of soft maple is such that it’ll deform into a shape and hold that shape, and as the rung swells, it’s less likely to crack than some other woods. But also, it will tend to follow that rung, so as the rung shrinks or swells, the resilience of that maple, the particular resilience which is not like hickory which is extremely resilient, but hickory doesn’t give much. Maple has a give to it and a return to its original shape, which is the resilience, that allows it to hold onto a hickory rung really tightly, I think better than just about any wood we’ve got. Even though hickory is a stronger wood for a leg or oak is a stronger wood for a leg, the issue with keeping a chair together is not just about, in fact I think it’s less about, the strength of individual parts, but it’s the ability of a joint to stay tight over time and under stress.
So that whole process, I think it’s a really good one to go through and to learn because of what it will teach you in going through that about all the things that we do in woodworking. So even though the furniture that I’m making now is not so much about the wood’s movement after assembly, we certainly take into consideration the wood’s grain orientation and it’s behavior after assembly in the way that we take any particular part out of a tree. I use that language because we actually buy logs and this kind of rolls into already some other questions that are on the list, which I’ll pick out in a minute, but basically, whether you’re working with a green wood chair making, Windsor chair making, 17th century furniture or contemporary furniture, it’s really important to pay attention to a given part’s orientation in the tree or it’s orientation to medullary rays and growth rings because it impacts how that piece is going to move.
The other thing that’s it’s really important to pay attention to throughout the process of managing your lumber pile and working with your wood is what the specific moisture content is of every part that you’re working with. Sometimes, if you really get a good sense of working with differential moisture contents, you can learn how to make judgment calls as to exactly what an okay moisture content is for a given part. It’s safer to go with 7% to 8% at assembly time for everything, but knowing whatever the ideal moisture content is for whatever you’re putting together today, it’s really important to know exactly what that moisture content is and you can’t do that really well without a good moisture meter.
When I was making greenwood chairs early on, I didn’t have a meter. I used other methods which were much less effective and I saw that later as some of the chairs got loose because the rungs were not initially dry enough or that unbeknownst to me, the legs might have been too wet as well. Again, you want that moisture content in the leg to be about 15% to 18%, not 20%, 25% because at 15% to 18%, there’s plenty of movement that that leg is going to make to tighten down on that rung without having the excess moisture that can cause too much swelling in the rung, which can compress and damage the joint beyond the movement that you want to get that structural tightness and strength in the joint.
So, if you’re not interested in making greenwood chairs at any point, I think it’s worth looking at the history of that and the process of that because particularly John Alexander’s book. Pete Galbert also has a fairly new book called Chair Notes and he talks about this as well. Drew Langsner, excuse me, has had a book out, I don’t think it’s in print anymore, but Chairmaker’s Workshop. All of those talk about … and Bruce Hoadley’s book, Understanding Wood, all talk about grain orientation and it’s importance to the mechanics and longevity of any given joint, whether we’re relying on a glue bond to stay tight, or we’re just asking the wood itself to behave in such a way that the joint stays tight. All of it, with all of the furniture that we make, is really critical in having the work that we do stay the way we intended it to stay.
We keep moisture meters going all day long. We’ve got one in the shop and there is not a day that goes by that one of us isn’t using that moisture meter. We track our wood. Just because it was kiln-dried and at one point it was 7% does not mean that it’s ready to cut a joint in. It might have picked up moisture, it might need to go in the hot room to dry out a little bit more, but we need to know and I think you need to know what the moisture content of the wood that you buy. One of the things that we’ve run into issues with, and I think my greenwood chair making history has really fed my alertness and attentiveness to moisture content, but whenever I buy wood from a retailer, I never trust that to be dry. I don’t want to put the longevity of my wood in anybody else’s hands, so I always check the moisture content of wood. And very often, in fact, I haven’t had a supplier yet provide us with wood that at least at one time or other did not arrive at way too high a moisture content to be usable at that time. So we get readings of up to 15% sometimes in kiln-dried wood, so it’s certainly something to be aware of.