Create Negative Space
The processes for creating the back and seat are similar. First I draw the piece full size so I can start to make the templates and forms. Both the two seat panels and two back panels are pressed over different shaped forms, yielding the two halves of each part. The panels are made up of either resawn laminations or commercially cut thick veneers. For this chair I chose to resaw 3/32″ laminations on the bandsaw. All of the panels were pressed using three layers of wood with Titebond 3 as the adhesive. Prior to the gluing process, all of the laminations should be cut to rough size.
When pressing large panels out of solid wood or veneer, it is sometimes necessary to edge-join material to obtain a larger piece. This can be done by placing the pieces to be joined side-by-side and stretching a few pieces of masking tape across the joint. Add one last strip all the way down the joint. Flip the pieces over, fold them along the joint (so the joint opens) and run a small bead of glue on the edges. Lay the piece back flat (closing the joint), stretch a few strips of tape across the joint on the face that hasn’t been taped yet and let it dry flat.
Form and Clamps
A vacuum press is great for panels with a single curve in them, but they have a more difficult time with a double curve. Hansuld chose to press the double-curved seat with a form and clamps.
Do Some Math
The curved part is clamped to a sled which runs on the table saw. Some math is required to determine the correct angle to tilt the blade to. Hansuld makes sure the workpiece is clamped securely to the sled before making the cut.
Spread the Adhesive
Hansuld uses epoxy (black in the photo) to attach the two halves together. The small ribs are only visible when you look directly into the void between the parts, and provide strength and a point of attachment for the seat. Notice the four small wood blocks that help locate the ribs during glue-up.
The mating, curved parts of the seat are glued together, with two curved cauls between the two parts.
Make the laminations
The back-rest curves are not very severe bends for our lamination thickness and can be pressed in the vacuum bag over a form. The seat panels both have a re curve in them, making vacuum pressing much more challenging. The vacuum press works wonders at holding pieces in place, but has insufficient strength for pulling laminations over severe or re-curved forms. Sometimes you can make this work by applying weight to your panel as the bag evacuates the air, but there is a higher chance of gaps in your laminations. For this reason, the best solution for pressing the seat panels is to use a variety of cauls and clamps. With my laminations stapled near the outer edges of the waxed form for location, I use two layers of waxed 1/8″ Masonite the same size as the panels for cauls as well as 2×2″ beams running across the seat clamped to the form on both sides. This method allows for the panel to be clamped tight to the form for both the convex and concave sections.
Cut angles, then clamp together
Once the laminations are dry, the reference marks on your original full-size drawing are transferred from the form to the panel. The panels are then cut close to final size. The angles where the two panels join (front and back) are cut using a tall auxiliary rip fence on the table saw with the panel clamped to it. The angles are taken from the full-size drawing by first marking a line across the two contact points the panel will have with the auxiliary fence, and then marking another perpendicular line. These lines represent the auxiliary rip fence and the bed of the table saw. A protractor or bevel gauge can then be used to determine the angle of each panel’s joint measuring off the perpendicular (table bed) line. Set the blade of the table saw to the necessary angle and run the part. Each joint will require a different set-up. Once cut, the joint will need to be tuned with a couple passes using your number 4 or 5 bench plane. After an initial cleaning, clamp the panels together along the joint to check the fits and adjust as necessary.
With the panel joints mating nicely the back-rest of the chair can be glued up, leaving the negative space between the center of the two panels. The seat of the chair, however, requires two ribs be glued into place. They will only be visible as you look directly into the void in the seat. The purpose of the ribs is twofold: they add structural integrity, and they provide some ‘meat’ to attach the seat to the chair frame.
The shape of the ribs are achieved by ripping 1/4″ off the width of each panel, placing these narrow offcuts together over the block you intend to be your rib and tracing the void. Carefully bandsaw it out and clean it up as you feel fit. If you require many parts the same general process can be used, but instead trace onto a piece of thin MDF or Masonite to make a template. You can create a jig for either the router or shaper, increasing the consistency as well as reducing the time it takes to create each part.
The rib locations are marked on the panel in relation to the stretchers of the chair frame. I hot-glue little squares of plywood on the inside edge of where the rib runs, which act as locaters for the rib to butt up against. They stay there forever, and will not be visible once the seat is glued up. With a dry run complete, the panels are glued up. I usually use epoxy for this glue-up, for the advantage of a longer open time, as well as its gap filling properties, in case my ribs or joints do not come together perfectly. Clamping beams are used along the joints as well as across the middle section of the seat to apply pressure along the ribs.
The completed seat and splat shapes are drawn onto the seat and back using hardboard templates and are bandsawn out. They are cleaned up by hand, profiled with a rasp and spokeshave, attached to the chair then finished.