Here is another part from the 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 parts 1, 2 and 3, 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 some of the drawings as vector drawings. The front illustration is from "The Interior of a Pianoforte Factory" from "A Day at a Pianoforte Factory" in Days at the Factories: Or, the Manufacturing Industry of Great Britain by George Dodd from 1843.
The fourth part describes completing the case and then preparing the keyboard.
Step 1: The Fallboard
The fall and back-piece are 3/4in. thick, and project sufficiently beyond the cheek to allow of the edges being rounded; the front of the fall thus answering as a lift.
The flap, B, fig. 1, will be hinged far enough back to give it the appearance of a panel, especially if the bottom of the lock-board is moulded as seen in diagram. It will also greatly improve the appearance if the back-piece is mounted with a 2in. ogee moulding, which may be shaped in 1in. walnut, backed with pine.
Step 2: Completing the Case
The top and bottom doors, C and D, Fig. 1, are simple framework, dowelled or tenoned together, the bottom door being fitted between false styles, E, to facilitate its passage between the truss legs, and is panelled with 1/2in. walnut. The top door is carried to inside the ends, which will look better if thickened at the front to match the cheeks; it also can be finished with panel and sconces, as in diagram, or with a fret and silk, according to taste. It forms a very effective swell if the panels of both doors are divided longitudinally, and hinged so as to open and close with pedal action.
The top is a 1in. board projecting about 1/2in. all round to allow a thumb moulding.
The legs most suitable to the style of case are either plain, bracket, or pillar, and drop, as shown in Fig. 2, either resting on a 2in. square-fronted show.
The case work is now complete.
Step 3: Purchase "'small' Work"
The next task will be fitting the action, or as it is termed "finishing." For this purpose it will be necessary for the operator to provide himself with a set of 16in. keys to match the size of key-bottom; they may be bought at from 38s. to £3, according to quality, and also a set of action or "small" work. This will consist of a set each of hoppers, levers, stickers, dampers (Collard's), and hammers, together with a hammer rail, and a socket rail, for the damper wires to work in, costing altogether about £2 2s. A check action would cost very little more, but would require considerably greater care in putting together - but, as it is, if properly regulated, a very great improvement both to tone and touch. A simple and at the same time very effective check action will be described further on.
Step 4: Preparing the Keys
In finishing, the keys are first prepared; a line ruled across them from 5 1/2in. behind the centre pin of the two outside A's will show the position of the front of the hopper mortice. To make sure of keeping the mortice in the centre it will be advisable to gauge from each side, the morticing being done with a 1/2in. chisel.
Two other lines will also be necessary to guide the boring for the touch leads, the first about 1in. in front of the hopper mortice, the other as near the end of the key as practicable. They will be bored with a 3/4in. centre-bit (the hole being about 1-16in. larger), melted lead can then be poured in, which must be punched when cool, to make it fit the hole tightly, as otherwise it would rattle.
Step 5: Clothing the Keyframe and Fitting the Keys
The key-frame can then be clothed; a round centre cloth of firm texture, about 1/2in. diameter, is required for the centre pins. This may be shaped with a gun-punch for the front pins; from 3 to 5 slips of ordinary baize will be necessary for each row of key-pins; or, if prefeerred, a set of key baizes may be bought, ready for fixing, at the cost of a mere trifle, from the small work makers.
At the back rail, for the key to fall on, are put 2 slips of baize, the front edge being protected by a groove made to receive them.
The keys are now ready for easing. This will require a small flat and a rat-tail file for the square and round holes. These holes must be filed till the key will gently drop to its place without pressure.
W. H. Davies
(from The English Mechanic and World of Science vol. 27, August 9, 1878, p.540)