The raw ribs are made longer than needed for adjustments. Place each rib at place, mark how much to saw off. The marked line is parallel with eighter rim or belly line. Trim conservatively, a little at a time, better leaving too long than too short.
Trim at pencil mark on band saw. Now the rib is closer to ideal length. Return rib to piano, mark closer to the end of rib slot, sand to length a little bit at a time on a belt sander.
The rib height and width are designed to support certain load on soundboard. If too wide to fit in original rib slot, open up slot rather than thin the rib.
For ribs whose two ends can sit on top of outer rim, place a square on each end, bottom of square against edge of rib slot on inner rim, place rib against top of square. The purpose is to locate the rib accurately. Mark on bottom of each end along the inside of outer rim, trim on bend saw then belt sander as shown above. The outer rim shape may be narrower on top than bottom. Leave room or saw out side of line on bandsaw for the first cut. Check again that all ribs are fitted just right in the rib slots.
On bottom of each rib, mark rib number, with a circle on belly side, no circle on the other side. Mark where the rib meets the inner rim. We are getting ready to roughly cut off the rib feathers.
Record the depth of rib slots, usually 3/16" on the first two ribs at treble on belly side only, 1/4" for the rest slots. Set up bandsaw fence to match the depth. Cut some scrap wood to make sure the sawing result is accurate.
Take out the original soundboard, trace feathered area on each rib according to the original. On bandsaw with preset fence, trim the rib ends to either 3/16" or 1/4" thickness, stop at the mark where rib meets inner rim. Remove fence, finish sawing the feather outside of pencil line to make the feathered area thicker, leaving room to be finely trimmed in the future.
Save the cut off pieces with numbers on. These will be used as spacers or cauls when ribs are glued to soundboard. Return all ribs into piano. Tape around and get ready to make soundboard pattern out of Masonite Board.