Building a chair with a curved back splat is challenging work, in part because the splat itself is tricky to fit. The tenons at the splat’s top and bottom aren’t parallel or in the same plane with one another. For my Chippendale chair, I simplified the measuring, layout, and fitting of the splat using this jig.

Something similar will work for almost any chair with a back splat, and other curved furniture parts, too.

The jig is two pieces of stock, joined end to end with a hinge joint. The opposite ends are cut with tenons that fit the mortises in the crest rail and the shoe (the piece above the back seat rail). To make the jig, cut the tenons first, then the fingers in the hinge joint. Remember that the jig must be long enough to match the space of the chair back. Slide the fingers together and drill a centered hole through both pieces for the hinge bolt. Take the jig apart and use a jigsaw, scrollsaw, or drill press to elongate the hinge-bolt holes in both pieces to allow for adjustment. To complete the jig, cut two throughmortises as shown.

To use the jig, dry-fit the crest rail to the tops of the posts. Loosen the wingnut and slide the jig’s tenons into the mortises in the shoe and crest rail, pivoting the hinge joint and elongating the jig as needed. Clamp the jig in place both top and bottom. When the alignment is perfect, lock the jig with the wingnut and remove the crest rail to free up the jig.

When transferring measurements to the splat workpiece, place the jig flat side down on the edge of the blank. The shoulder angles determine the angles that will be cut on the ends of the splat. After establishing the angle of the shoulders (and the angles of the blank ends), and scribing the front and back of each tenon with a marking knife, remove the jig. Add the splat design’s outline to the front face and the sides, and you’re ready to start cutting.

Jim Richey

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