The 'Branch Joint'

 

The branch joint is one of the central visual and structural elements of this rocker (for better or for worse). I knew it needed to be strong. The individual components were certainly strong enough. I decided that all three of them needed to extend all the way down to the rocker (It doesn’t look that way on the outside, but you can see it on the inner faces of the legs. I’m still thinking about switching that around).

                    Inside view of the bending ply mock-up

                 Inside view of the bending ply mock-up

   Outside view of the mock-up. Still a bit of work to do to get everything centered.

Outside view of the mock-up. Still a bit of work to do to get everything centered.

And I wanted as much contact between parts as I could get. One last thought was that the outer parts would be stronger with an ‘L’ shaped cross section. What I came up with after much sketching and experimenting (and a number of unsuccessful jigs) was a complicated lap joint.

Because the faces of the bent laminations were not quite good enough to join, I started by re-shaping the front face of the back leg. I then reshaped the back face of the arm support to match it exactly. These two were then glued together, and then the front face of the arm support was faired. Next came a curved rabbet in the joined parts. To match this, I re-shaped the back face of the front leg, then cut the curved rabbet in the front leg. In the final assembly, I do shoot a couple of screws through the top of the joint for good measure. These get plugged, and a layer of matching veneer is laminated over the entire bottom of the ‘front leg’.

Altogether, it takes two sets of 6 jigs do both sides of the chair.

The hard part of all of this was getting all of the shapes and routed curves not only to match up, but to flow as well. It’s reasonably quick now that everything works, but it took forever to get it the way I wanted.

                                        A sketch of what's going on in the joint

                                     A sketch of what's going on in the joint

Joinery, ChairsJeff Miller