To minimize trips up and down ladders to measure, cut, test-fit, re-cut, shim, and fasten all 230-plus mitered joints (19 bays total, each with at least 12 individual joints) of the underside trim for the coffered ceiling, we decided to cut and assemble as much trim as possible on work tables below. Our plan was two-fold: First, we’d assemble the horizontal underside trim into a few large sections (as shown here) and lift them into place; then, in each bay, we’d assemble the fascia trim as four-sided boxes, lifting them into place as well.
The Usonian miter. One of the challenges in building the ceiling was joining the four-way miters at the intersections of the highly visible undersides of the beams. Cregg borrowed this striking detail from a complete restoration of a Frank Lloyd Wright Usonian house he’d worked on in California. In our case, to make that joint strong enough for lifting the trim into place as a unit, we planned to use a combination of Festool Domino tenons, pocket screws, and yellow glue.
Upfront, we did a lot of careful measuring, layout, and trial-and-error to make sure the joint would hold together. On a rock-solid, older-model 10-inch Hitachi sliding compound saw, we fine-tuned the cut angle (micro-adjusting the saw’s cut angle was necessary to achieve absolute accuracy for all eight miter cuts on the underside trim).
Rather than reset our hard-won angle for the opposing cut, we registered the opposite end of each 1x5 board against a flip-stop clamped on the saw’s extension table and flipped the board to cut the opposing angle. This also ensured exact uniformity between corresponding pieces.
The Domino provides three mortise widths—one snug, one elongated, and one even wider—to allow for some lateral adjustment when pieces are aligned. We cut a snug mortise on one face of each miter, and an elongated slot on the opposing face, paying close attention to which piece went where in the assembly.
We then plunged-cut mortise slots into the solid cherry with the Domino joiner.
We pieced together the intersecting joints with the finish face down, just as it would be when lifted into position. Here, Tim Towle of Artisan Builders assembles the underside trim on a worktable below the ceiling.
To help properly assemble the joint, we marked the mortise and pocket-screw layout on each joint.
The tenons were glued in first with yellow glue.
The pocket screws and Domino tenons were installed in a fairly tight space and were placed in a radial pattern to help avoid one another. The resulting four-way mitered joint was robust, and we couldn’t break it apart.
V-notch miter. In the dining area, the alignment of the bays shifts from linear to offset. The junctions called for a “downscale” version of the four-way joint, in which only one double-mitered end intersects the running edge of the perpendicular member in a reciprocal V-notch, like an arrow penetrating a target. We employed the combination of Dominoes, pocket screws, and glue to make the connections.