First, the ribs (sides) need linings attached. Kerfed linings are common, as are multiple small block linings used in the Spanish method of construction. I use solid linings for 2 reasons: extra stiffness and less sonic loss. If you think of a make-shift music studio that uses egg cartons to create an anechoic chamber, this is similar to the effect that individual block linings and kerfed linings will create. Ultimately, loss of echo inside the guitar’s body will lead to loss of volume, however slight that may be.
After the linings are glued, they must be shaped to a triangular profile and grooves are cut to allow for the inset of the horizontal braces (back struts & harmonic bars) Then, the edges to be glued are planed and sanded to match the curvature of the back and the soundboard as required.
Neck set and angle are finalized once the soundboard and back are attached. Hence, this is an extremely critical step in creating a guitar that sounds and plays well.
After attaching the soundboard, excess glue is scraped away and the top is cut and filed to the exact shape of the ribs. The same is done for the back but it is more challenging since excess glue must be scraped with access only through the soundhole.