How We Build a Rocking Chair — Crest Rails
We select the crest rails so that the growth rings are symmetrical to a vertical centerline. The crests are the hardest parts to find in the stock. It is remarkable how little wood will meet the specifications for this part. We look for them first and rarely find more crest rails in a quantity of wood than the number of chairs such a quantity will make.
We laminate the crest to obtain the necessary curvature (#1). Most crest rails of the chairs you find and see are too flat for comfort.
Like most chair parts, the crest is rough cut at the bandsaw (#2).
Like for most chair parts, I built several jigs and fixtures to facilitate the work on the crests. Aided by the jigs and fixtures, we use the router to "true" the curves (#3) and cut the mortises in the crest rail. These curved surfaces and mortises are precisely produced so that the mortises lie along the curve equidistant from the edge (within a tolerance of .010").
I built a machine to sand the concave curves of the crest rail (#4) and other parts. Presumptuously, I thought I had invented it, but later found out that such machines are common in areas where furniture has traditionally been manufactured. It's called, appropriately, a chair back sander.