My keyboard is for a square piano and is more complicated than the one for Mr. Davies upright. The lengths are all different and the rails are at angles, the front and back ends of the keys are offset sideways, they aren't uniformly thick and besides there being fewer of them the keys as well as the action parts they set in motion are smaller. It works the same and has the same ordinary arrangement, though, with seven white and five black keys in each octave and no breaks in the back spacing so the steps are the same as for Davies' upright, and it even has the parts needed in part 5 of his instructions.
A keyboard closer to Davies' is described in "How to Make an Organ Keyboard" by "M. W." first published in Work Illustrated in 1884.
Step 1: Materials: keyplank
Keyplanks are glued up to the width required out of a few boards with the grain going the long direction of the keys. The wood they're made of has to be dry, straight grained and free of knots, as well as stable with changes in humidity and relatively strong and easy to work. They're usually a light weight, soft wood with little difference between early and late wood, like soft white pine or basswood. English piano engineer Samuel Wolfenden considered pine a little too soft, and like the famous German piano manufacturer Julius Blüthner considered basswood a little too unstable, depending on where it grew. Different woods can be combined to make better advantage of their good qualities.
The keys shouldn't bend so they should be relatively thick, depending on the amount of space there is, but usually they aren't much more than 2.5cm or less than 1.5cm. Shorter keys can be made thinner, and thinner keys can also be made stiffer by increasing the height just around the fulcrum, using stiffer wood or by reducing the stuff they have to move.