Chair no. 1 – Fabrication Part 1

With the design for chair no. 1 more or less decided, I forged ahead with fabrication. One of the first choices I needed to make was what type of wood to use for the chair. I ended up choosing white oak for a couple reasons. One reason was out of convenience. A friend at my shop had a small stockpile of oak on hand, making it easy to choose a few boards and buy directly from him instead of having to go to the lumber yard. The other more important reason, is that white oak pairs really well with Danish cord which I planned to use for the seat. The colors are similar so there isn’t a glaring contrast between the wood and cord. Similarly the texture of Danish cord and porous oak also complement each other. For the past few years my wife and I have had two stools in our apartment that we use daily. Both have Danish cord woven seats, but one stool is made of cherry while the other is white oak. I’ve always preferred the white oak version for the reasons described above, so I wanted to follow suit for this chair build.

Arm/Backrest Joinery

I decided to make the arms and back rest out of solid wood, and carve out the curvature that I wanted. The other common options for forming a curve would have been to do a glue-up lamination or steam bend a piece of wood into the desired shape. Both are decent options and they have their pros and cons, but since this chair is a prototype of sorts I didn’t want to invest too much time in making jigs that would be necessary for both of those processes.

So I decided to glue up the arms/back from solid pieces of oak that I joined with splined miter joints. Below you can see the joints after cutting on the table saw. These pieces of oak are each 40 mm thick and about 95 mm wide; big enough to allow me to glue up the arms in a big U-shape and cut out my desired curvature.

Here you can see the splines. I made these from the same stock of white oak. The splines aren’t wide enough to cover the whole length of the joint, but that didn’t matter since I would be cutting the bulk of the corner off. When I glued up these joints I made sure that the splines were in the correct location using a template as a guide.

Here is one corner of the arm/back rest after assembling and gluing. Before cutting the shape of the arms I first cut the mortises that mate with the tenons in the legs. These are all angled, at about 10 degrees front to back, to accommodate the slope of the arm/back rest. There wasn’t a great way to use the mortiser for cutting these joints so I cut them by hand.

Drilling a couple holes and then chiseling out the waste for all four mortises went pretty quick. I’d much prefer to cut mortises using a mortiser but in a pinch it’s nice to know how to cut them by hand. In the picture below you can see the finished mortises and the inside edge of the shape that I planned to cut from this glue-up.

Shaping the Legs with Power and Hand Planes

I choose to make the legs round with a taper towards the top and bottom ends. Before shaping the legs I first cut the mortises for the seat stretchers as well as the tenons that would join with the arms/back. It’s far easier to cut joinery on square stock than round. My apologies as I forgot to take pictures when cutting the mortises and tenons, but overall the process was pretty straightforward, with the exception of two sets of mortises that needed to be cut at compound angles to accommodate the seat stretchers.

With the joinery cut I could proceed with shaping the curvature of the legs. Ordinarily I would have done this work on the lathe but while the shared shop I’m currently using has 4 lathes, they all have small beds with no extensions. Meaning the legs were too long to mount and turn on the lathe. So I shaped the legs with power and hand planes.

I started by making a simple template to layout the curvature on each leg. Then I began planing the curvature using a power planer to cut right up to my layout lines, and from there I refined the shape with kanna (Japanese hand planes). Below you can see the overall curvature after cutting two faces of each leg. At their widest near the middle the legs are 40 mm (1.6 in.) thick, and taper to 30 mm (1.8 in.) at each end.

With the first two sides shaped, I used my template to layout the curvature on the other two faces of each leg and cut the same shape. At this point the legs were still square in cross section.

Then I proceeded take off the corners of the square legs, essentially turning them into octagons. At the same time I also cut the same curvature, again using my template as a guide.

From there I repeated the operation one more time, by focusing on removing the corners of the octagon shape. This step brings the legs much closer to a round shape. I found I could set the electric power planer to a really light cut (0.5 mm) and had a lot of control over fine tuning the shape, without the risk of hogging off too much material. I love hand planing, but it’s labor intensive, so I went as far as I could with the electric planer before switching to my Japanese planes.

Below you can see a bit of the tenon joinery for joining the legs and arms. As I mentioned above, I cut the tenons to size before shaping the legs, but left them extra long and also left material on the sides of the tenons for scribing. I planned to scribe the shape of the arms into the legs, so it’s important to leave material for that process. We do the same thing in carpentry when scribing posts to beams. (More on scribing later.)

Once I finished roughing out the shape I used a couple hand planes to further refine the legs. Essentially my goal at this stage was to bring each leg as close to round as possible, while also shaving an even series of facets along the entire surface. I like the look and feel of the legs that are shaped this way. You really can’t see the facets. The porous grain of the oak sort of blends and disguises the faceted surface, but there is a pleasing texture that becomes apparent when you touch the surface. I also like this detail because it’s not something you will ever find on mass produced furniture.

Scribing the Seat Stretchers

With the legs more or less complete, I moved on to cutting and fitting the seat stretchers. These pieces are pretty simple. Just a simple tenon on each end and a light curve for the outside edge. I also used a router to round-over the outside edges to ease the corners that the Danish cord will wrap around.

The tricky bit of work for these stretchers was scribing them to the legs. This is a bit of a fussy step, and I’ve seen other chairs where these joints aren’t scribed. Rather they are often simply cut square probably as a time saving measure. The Danish cord will more or less cover these intersections so it’s not a detail that cheap chair manufacturers will likely care about. The problem with that design is that all of the stresses and forces that come from a person sitting/leaning in the chair are placed on the tenons alone. In addition to the tenons themselves, having a solid shoulder connection between the legs and each stretcher will increase the strength of the joint greatly. So I decided to scribe the shape of the legs into the shoulders of each stretchers.

For those unfamiliar with scribing, the process involves using a tool like a compass to mark the curvature from one piece (in this case the leg) onto the mating piece (stretcher). From there you cut along your layout line to achieve a matching fit between the two pieces. Scribing is not easy, so it usually takes a couple rough passes to get the fit close, and then a bit of fine tuning to dial in a nice joint.

Below you can see one stretcher tenon and shoulder after an initial scribe and rough cut.

Here’s the scribe I used for this process. This style of scribe is commonly used by Japanese carpenters. It’s simple a piece of steel, ground to a sharp point, and sandwiched in a folded over piece of brass. (The steel pin gets soldered to the brass.) The brass is folded over such that a pencil can be wedged in and tightly held by the brass.

Here is one connection after a touch more scribing. After I got each joint to this point, I marked the points of contact one more time, and then removed the stretcher to cut the high points. I wasn’t aiming for a perfect fit with these joints, but more like 90%. Scribing can be a real time suck especially when you are trying to make the fit perfect, and ultimately these joints won’t be seen so I wasn’t concerned with aesthetics as much as providing a decent connection between the stretchers and legs.

With the stretchers scribed, I did a quick test assembly to see how everything was coming together. You can see in the picture on the left how the side stretchers sit higher than the front and back stretchers. It’s also not super apparent in the photos but the sides stretchers also have a slight angle to them, heading downwards toward the back. That little bit of angle makes a huge difference in comfort compared to chairs with a flat seat.

Well, when I started this post I thought I would be able to fit everything from the fabrication into this one post, but turns out there are a lot more photos and details to cover. So stay tuned for round 2 next week.

Thanks for following along.

P.S. bonus points to anyone who spots the patches where I covered up a few mistakes in the legs 😉