Make a Modified Scarf Joint

Author: Jonathan Otter
Photos: Jonathan Otter
Published: August September 2013
Modified Scarf Joint
Modified Scarf Joint

With all their angles, chair joints often pose a challenge. This East Coast furniture maker has adopted a unique joint to create a beautiful chair.

I have developed this method so I can create a continuous arm Windsor chair without the troubles associated with steam bending. I make the back/arm from three separate components: the back hoop and the right and left arms. Then, using a modified scarf joint, I join them into a single crest.

Rough Cut
Otter roughs the scarf joint out on the bandsaw. The next step is to smooth the freshly cut rough surface with a sharp block plane.

Make a Shoulder
With the arms clamped to the mitre gauge Otter cuts the 1/8” high shoulders on both arms.

Mating Joint
After making a small notch for the shoulder, then a rip cut to establish the side of the joint, both on the tablesaw, Otter separates the waste from the workpiece on his bandsaw.

Glue Up
With both joints machined, hand-screw clamps are used to bring everything together.

Templates for Accuracy 
Even if you’re only making one of these chairs, it’s a good idea to use a template to mark the two arms, as it ensures accuracy and repeatability.

The Right Tool
 Some careful cutting on the bandsaw removes much of the waste. Further shaping of the arms and back is with an assortment of hand tools.

Beautiful and Strong
The completed joint, with wedged tenon directly through its center.

Make the three parts

Once the arms and back are made, I dress one edge square to its face. Then I rip the arms and back hoop to width on the tablesaw. I also mark each arm and the back hoop to keep them oriented correctly.

The scarf joint

The joint I use is a modified scarf joint. A feathered scarf joint works well, but it is preferable to put a small butt on the top to make the glue line less visible. Beginning with one arm, I mark a line that will produce at least 4″ of gluing surface, bandsaw it, then finish it to the line with a razor-sharp block plane. I transfer this line to the other arm and repeat the process. It is critical to make this surface flat and exactly the same on both arms.

Next, I cut the feathered point off both arms. I place the freshly planed surface flat on the tablesaw, with the edges tight against the cross-cut jig, then trim it so the end of the joint measures at least 1/8″ in thickness.

Then I lay out the mating joint on the back hoop. This half of the joint differs from that on the arms; it is cut as a simple lap joint. I lay out the joint by measuring down from the centre line mark on the back hoop. This joint should be long enough to accept at least the full 4″ of the arm joint. For visual balance it’s crucial to make both joints identical. I laminate the back hoop with plenty of extra material in the straight section. This helps me layout the joint, as well as orient and control the part during machining.

After cross cutting to the line at a depth of 1/4″, I raise the blade to its full height and set the fence so the blade will cut on the waste side of the joint depth – 1/4″ in this case. I cut as close to the cross cut as possible. The tablesaw cannot complete this cut because the blade is round so I finish the cut with the bandsaw, then clean the surface with a chisel and repeat on the other side.

The glue-up

During glue-up the two long-grain surfaces need to be clamped together (for strength) and the shoulder and butt end need to come together (for looks). Cover the surfaces with glue and clamp them. Hand-screw clamps are great for this task.

Shape the joints

Once dry, I lay out the shape of the arms with a template. I start with the bandsaw to rough the arm out, then further contouring is done with rasp, spokeshave, scraper and sanding – a fair curve is crucial. It’s a good idea to leave the final shaping and sanding until the spindle holes are drilled. I strengthen the scarf joint by running a wedged tenon spindle right through it. The result is a joint that is strong and pleasing to the eye.


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