This continues a series of articles by W. H. Davies of Liverpool published in London in The English Mechanic and World of Science in July and August, 1878. You may also want to read instructables made from part 1 and part 2, and you can download a scanned version from Google Books. The piano he describes was old fashioned at the time and hasn't been manufactured for a long time, and Mr. Davies services and patterns, as well as the parts he recommends, are no longer available so some options might be considered if you follow his directions. I edited and broke it up a little, and reproduced the illustrations as vector drawings. The picture is a detail from "Ateliers des tableurs" in Julien Turgan's "Fabrique de Pianos de MM. Pleyel, Wolff et Cie" from 1865.
The third part describes completing the soundboard and bridges, stringing, and then starting the case work.
Step 1: Fixing the Soundboard
The soundboard is now ready for fixing to its place; with a wooden back it is screwed from the front into the wedges and bracings around the bent side, and nailed to the lining slips with clout-headed tacks (afterwards to be covered with varnished slips). It is better to have the holes bored and counter sunk so that the soundboard may be quickly fastened before the glue (which should be rather thin, and liberally applied) has time to chill.
Step 2: Downbearing, and a Description of the Top and Bottom Scales
In an iron back, the linings only are to be glued, the remainder being fastened with screws from behind, or with small bolts, the heads of the screws being insulated with a felt button before "marking off;" the bridges must be planed to proper height, so that the down bearing of the strings may not be too great; at the treble the plank bridge and lower bridge are level, and the straight edge laid across them should be 1/2in.* above the bent side or pinning edge, the remainder of the lower bridge being so regulated that straight edges laid on the bridge and touching the pinned edge should be of the same angle everywhere as the one at the treble; the plank bridge can then be planed to the same thickness throughout, which should be about 5/8in.;* the top and bottom scales are now placed in their respective positions.
It may be necessary to explain that these are 1/4in. slips of wood, with holes bored at regular distances, those of the top scale corresponding with the hammers, those in the other rather closer together, or, as it is termed, "contracted." For convenience of reference they are also lettered to the gamut in use, a pin is placed in each hole consecutively, and with the straight edge leaning against them; a line is ruled across the bent side, lower and top bridges, this line representing the right-hand string of each note.
Step 3: Drilling, Pinning and Notching the Bridges
The first or treble hole of each should be 2 1/2in. from outside the lining, the holes of the top scale exactly covering the strike line, the lower laid on the bottom lining. As in an iron back the pins are already in, the lower scale may be dispensed with, the straight edge being laid at the right side of each pin instead, and ruled across the bridges as before; when they are ruled they must be punched with two or three holes as determined, taking care not to punch too near the edge; they are then bored for the bridge pins. I find for this purpose a 1-16in. spoon bit, set in an Archimedean drill stock, to be the steadiest.
The holes have a slight lean - the top bridge and top row of lower bridge towards the bass end, and the lower row of holes the reverse way.
The bridges have then to be glass-papered and blackleaded, the wood then cut away from the front of the holes, so that nothing touches the vibrating portion of the wires but the bridge pins.
Step 4: Drilling the Wrestplank and Stringing
The plank is now to be marked and punched for the wrest pins. As it is necessary to have a "side bearing," these lines must be ruled with a bevel, the angle bearing a proportion of 1 in 3, and represents the centre of wrest pin. To keep as much as possible out of the grain line, it is better to bore the holes in four rows (or six for a trichord); see diagram Fig. 1, the lines pencilled and afterwards scraped out.
The sizes of wire for stringing (music gauge) are 12 notes of No. 14, 12 of 15, 11 of 16, 16 of 17, 4 of 18, and 2 each of 19 and 20; for a trichord 1 size less so far as it extends; but before putting the strings on, a slip of baize must be laid all along the edges of the bent size and plate, to prevent the wire from jarring against them.
Step 5: The Case
The back is now ready for the case.
In accordance with suggestions I think a case made after the French pattern (see diagram Fig. 2), and of solid walnut, will be most suitable for amateurs, as it will require neither special tools nor cauls for its construction.
The ends are 1in. thick, 48 1/2in. long, and 12in. wide. In glueing on, a margin must be left all round the lining; see dotted line (Fig. 2), the cheeks (C, Fig. 2), 1 1/2in.* thick by 12 by 7in. then being dowelled (not glued) to their position - viz., 22 1/2in. from bottom of end, and flush at the outside.
The key-bottom, being a framework of 2in. pine, with a back rail 1in. by 4in. wide (see Fig. 3), is then fitted between them and dowelled, by template, 1 1/4 in from their front edge, to allow for the lock-board, care being taken that the back of the key-bottom is not touching any portion of the bridge. To make sure of this it is advisable to try all together before glueing.
Any measurement required may be taken from Figs. 2 and 3, they being drawn to a scale of 1 in 12.
The front plinth can now be got out. This is let in between the ends with the exception of a shoulder projecting beyhond them 1/4in. and forming with the side plinths a border all round of that thickness.
An inside bottom (C, Fig. 2) is to be fitted to fill up the space between the ends and plinth. This can be dowelled or nailed through from outside the end, as the side plinth will cover the holes.
W. H. Davies
(from The English Mechanic and World of Science vol. 27, August 2, 1878, p.514-515)