My chair plans called for turned, tapered, and steam-bent back rails, so I needed a way to find the centerlines to position the holes for the back spindles. This easy jig did the trick.
020803 100528039

Drill a pencil-size hole through a 34 x 112 x 112 " block, cut a V-shape notch into it, centering the notch in the block. Glue a small bubble level on one edge, and insert the pencil, as shown. Working on a flat, level surface, with the pencil pressed to the rail, run the V-block along the rail while keeping the bubble centered. The resulting centerline follows the tapers, bends, and curves of the rail.
—Ted Sheroke, Medina, Ohio