The old slotted screws are of very good quality, worth cleaning and polishing. The hardware stores sell mainly Philips crews and those with all different types of heads, but slotted. The resurfacing method here is taught by Mr. Jude Reveley, shop owner of Absolute Piano Restoration.

When the hammer top hits all strings of one note at the same time, the maximum power is transferred. To make the adjustment, the action must have been finely regulated and the piano freshly tuned. The cheekblocks are better in place to make sure the action is at the correct position. This hammer to string mating process is learned from Mr. Eric Schandall. 

This is a figured-out-by-self note after all sorts of failures and damages. I do wish to learn how factories and other workshops offset the wires by the plate strut. What damages have been made? All that one can think of.
(German practice on the first paragraph: Diese Methode habe ich selbst herausgefunden. Ich möchte gerne erfahren was die Manufakturen und die andere Werkstätten machen. Ich habe so viele Teile zerstört, die man sich vorstellen kann.)

When pressing the sustain pedal, the dampers shall rise at the same time as a union. This timing adjustment method is from David Betts. Usually the process takes 1-2 hours when the dampers, wires, and regulation are in decent shape.

It all starts from nightmares that the damper system was put in wrong, or the parts were broken in pieces, and there were dust in the package where worms crawled everywhere eating and chewing happy.

​We try our best to replicate the backaction exactly as the original unless where were flaws in the old system. Every screw hole has to be marked and drilled precisely and spaced evenly. Usually music, podcast, or any distractions are banned for the day. The assembly process takes about 8 hours. This is a Renner Backaction. The assembly training material can be found on the Renner USA website :
ttps://rennerusa.com/training-manuals/

Jude, the shop owner, uses several species of softwood for ribs. One piano usually has two kinds depends on the area, load, and more. After his calculation of ribs on each piano, we start the milling process. Each time of milling is a new practice. And each time is nerve racking to make it right, or almost right.