Boggs Side Chair Build #25: Turning, Part 2

One of the most critical parts of the side chair are the joints between rungs and legs. The quality of these joints have a large impact on the strength of the chair and it’s ability to support a person and resist wracking. At the turning stage there are two things that I do that contribute to a strong joint. The first is control of moisture content. For about a week prior to turning I keep the rung blanks in a small kiln in order to reduce the moisture content to bone dry, probably about 4% or so. After assembly the rung tenons will take on moisture and swell slightly within the joint. The second is the precision of the fit between the rung tenon and mortise in leg. The rung mortises are 5/8″ diameter or .625″. I have fine tuned a wrench and use it as a very precise caliper that allows me to turn the tenon diameter to within ± 2 thousandths of an inch. This precision allows for complete wood-to-wood contact within the joint. The first step is to mill the rungs out of the larger board as described here. Because the finished rung is a tapered cylinder, the end grain orientation does not matter since the rung will be rotated to correct end grain orientation at the time of assembly. Straight long grain, however, is important and care should be taken to mill the rung blanks parallel to the grain, not an arbitrary milled edge in the rough board.

The final diameter of the rung at it’s middle is between 1″ and 1-1/16″. With 9/4 (2-1/4″ thick) rough boards it’s possible to mill two 1-1/16″ square rung blanks. This does not leave much room for error when turning, so recently I have been milling my rough boards at the sawmill to 10/4 (2-1/2″ thick) which allows me to get two 1-1/8″ square rungs out of a single thickness. The 1-1/8″ rung blanks have enough extra dimension to easily turn the rung to full diameter in the middle.

To mill the rungs from the rough board I begin by face jointing one face, then edge jointing one edge. I set the bandsaw fence to make a 1-1/8″ cut and mill out the square blanks. Here are a set of rung blanks that have been milled square. On the left are lower rungs milled from the same soft maple as the legs and slats. There are six lower rungs, but I always mill some extras just in case. On the right are the seat rungs milled from hickory. The seat rungs are put under enormous pressure from the hickory bark seat and need to be strong enough to withstand that pressure and the additional stress of a person sitting in the chair. Soft maple and some of the other softer hardwoods (cherry and walnut) are not strong enough for seat rungs. There are four seat rungs in the chair, and again I’ve milled one extra. Oak and hard maple can also be used for seat rungs.

The next step is to knock off the corners making each rung blank into an octagon. This reduces the physical dimension of the blank allowing it to dry faster and more thoroughly and also makes the turning go a bit quicker. I use a simple v-block set up on the bandsaw to cut off the corners. The v-block holds the square rung stock at a 45° angle relative to the blade. The v-block is held tight against the fence which can be moved to adjust the amount of the cut. Since my bandsaw has a slot in the table I use a feather board to hold the v-block against the fence. If your table does not have a slot simply clamp the v-block to the table. The v-block also has a small board attached to the bottom front edge that keeps the v-block from moving forward.

Here’s another shot of the v-block set up on the bandsaw.

To begin I draw an octagon on the end of one rung. I described a no-measure method of drawing an equilateral octagon here.

I set the rung blank into the v-block and align the outside edge of the octagon with the bandsaw blade as shown here.

Then I test the set-up by making two shallow kerf cuts on two opposite corners of a blank and measure the distance between the kerfs. When the distance between the kerfs matches the dimension of one side of the square blank I’m ready to go. In this case my blanks are 1-1/8″ square so I’m looking for 1-1/8″ between the kerfs.

Now I run the square blank through the saw with the v-block guiding the cut. After the first cut I rotate the blank 90° and make the second cut. After four cuts my square rung blank is now an octagon. At this point I put the rungs in a small light bulb kiln to dry for about a week. After a week the rung blanks should be bone dry, probably about 4% moisture content, and ready to turn. Here is the set of rung blanks for this chair. They are all cut to final length and I’ve marked centers on each end. The four hickory seat rungs are on the left and the six soft maple lower rungs are on the right. I always have a few extra rung blanks in the kiln should something go wrong while turning.

Now I am ready to mount the rung blank in the lathe. I align the steb centers on the center marks on each end. The only part of the rung that really needs to be centered is the middle of rung which will be turned to full diameter. Occasionally, after a week drying in the kiln, the rung blank will be warped. In this case I do my best to center the middle of rung by measuring the distance between the side of the rung and the tool rest. Then I rotate the rung 180° and measure again. If the measurements do not match I can reposition one steb center on the end of the blank using the center marks as a reference. I measure again and adjust as necessary until the distances match. Next I rotate the rung 90° and repeat with another two opposites side. Once I am equidistant all the way around I am ready to turn. This will make one end of the blank off center, but since the ends will be turned down to 5/8″ diameter it won’t matter. One way to avoid this is to make the rung blanks slightly oversize which can compensate for any warping. I recommend rung blanks that are 1-1/8″ octagons. This leaves plenty of material to turn to full diameter of 1″ to 1-1/16″ at the middle of the rung.

The rung blanks are turned to the shape illustrated here. The tenon is turned to 5/8″ diameter using three cuts of the 3/8″ bedan which leaves a flat surface 1-1/8″ long. The remaining 1/8″ of the tenon length is actually a slight taper into the body of the rung. The middle of the rung is 1″ to 1-1/16″ in diameter. 

Here is a video of the entire turning process. I begin by mounting the rung blank in the lathe as I just described. Then I turn the tenons using a 3/8″ bedan or beading and parting tool. Next I rough the shape of the rung with a roughing gouge. And finally I put a finished surface on the body of the rung with a skew chisel. The surface left by the skew chisel needs little or no sanding. But the skew chisel can be a difficult tool to use, especially for beginners. Don’t let that stop you. You can always just shape the rung with the roughing gouge and sand to a final finished surface.

I always start the skew cuts at the middle of the rung and move downhill from the middle to the ends. This photo shows the angle of the skew chisel for making the cut from right to left. Refer to the video to see how I actually hold tool while turning. With this angle the tool takes wide shavings and results in a very smooth surface. Always move the skew chisel downhill and cut with the lower third of the blade.

To cut from left to right the tool is rotated as shown here. In this position the blade is held at an equivalent opposite angle. Refer to the video to see how I actually hold tool while turning. Again, I always move the tool downhill and cut with the lower third of the blade.

Here I’ve drawn the angle that the blade of the skew contacts the wood beginning at the middle of the rung and moving downhill toward the ends. The angle that the tool engages the rung is identical whether I am moving right to left or left to right.

The mortise is .625″ and Brian tries to get the tenon diameter within .002″ of that. I am generally happy with a tenon diameter between .620″ and .625″. Here I’m measuring the tenon diameter — 625 thousandths — right on the money!

And here is a completed rung. I’ll put the rungs back in the kiln until they are needed for assembly in order to keep them bone dry.

With the rungs complete I’ve now finished shaping all the parts for the chair — rungs, front legs, rear legs, and slats. The unassembled parts don’t look like much, but it’s all I’ll need to make a chair.

The next phase of building this chair involves drilling the rung mortises into the legs. I’ll be explaining in detail how I figure out drilling angles. All of the rung mortising is done on the drill press with simple, but highly accurate jigs for holding the legs at the correct angle for each mortise.

Jeff Lefkowitz


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