Let's review aftertouch

Indeed. You probably need to increase the let-off. Before doing it individually, consider the general let-off which for the C3 of 10mm (the blacks [should be] somewhat less and must have the same aftertouch as the whites). First check the key level; some might be lower and those specifically would have less let-off.

So: check, by placing a straightedge on the keyboard, the general level of the keys

general let-off check

individual key check

P.S. you must create a cardboard washer as thick as the aftertouch value you have established. This will be your control jig. Placing it under the key and pressing the hammer, it must not "escape" or, at most, it should escape with difficulty if you apply a certain pressure. You will add or remove pieces of cardboard depending on the measurement result... but only after having established the general let-off. You must therefore have a 10mm jig for the white keys and a gauge, even a homemade cardboard one, that can allow you to detect the level of the blacks and their let-off.

For the general let-off, you can use (even if it is not a very orthodox system) the screws of the frame supports... but only by one or two tenths. Naturally, by tightening, the let-off increases and vice versa. The side blocks must be fixed.

With the correct let-off, the piano becomes more expressive and the pianist can use different types of touch without compromising the escapement and the fall of the hammer. This is especially fundamental in pianissimo. It is also important in the "jeu perlee" that the French often indicate and/or recommend in their music.

Thank you Pianoexpert,

the let-off is 10mm and the level is perfect, so the piano is only a few years old and the rollers are in excellent condition.
the problem is that to have a minimum of aftertouch it was necessary to bring the hammers to 45mm from the string and now if I want more aftertouch so as not to lift the hammers again I must increase the let-off..

how far can I take it without compromising the performance of the piano?

10.3 max. The hammer rises if the after is too much. Also check the drop and the spring tension. It is possible that the center pins are not very fluid and therefore the springs are too heavily loaded. Also check the friction. 45 mm is fine.

So if I can lower the backstroke, I will proceed in this direction; I'll see how much is needed without touching the 45mm hammer-to-string distance.

The drop is 1.5-2mm and the spring is adjusted to rise decisively but without a snap.

I will post the result as soon as it's done

Thank you,

How wonderful! I think we are almost there..

I kept the 45mm hammer-to-string distance and increased the let-off as recommended.

Actually, with the action on the bench and the ruler on the keys, a difference of a few tenths of a mm is noticeable, but I didn't want to disassemble the action assembly and right now I don't even have key center bushings. I will do it during the next regulation.

The single let-off was also less than 10mm and I brought it to about 10.2mm using a 1.5 shim for the aftertouch, so that the repetition lever snap occurs with effort and slight pressure.

Now I see the small hammer rise after the escapement.

Escapements at 3, 2 and 1.5mm

Drop 1.5-2mm

Let-off (parata) approx 12-13mm

The sensation, I must say, is strange; it's incredible how a few tenths of a mm can change so much. I have to get used to it. Everything is more controllable though, and the repetition has also improved, but what I don't understand is how the tone in general can improve. It feels as if it has been tuned again.

But why do the Japanese make such an insufficient background, I don't understand..

Sometimes there is a small swelling of the front hammers....or sometimes it is intentional to make the keyboard seem easier!

A question, does 45 mm apply to the entire hammer rail or are there sections that need to be adjusted differently? Many thanks.

45 is not mandatory for all instruments. Regarding uniformity, even Steinway says that, from 47mm, they can go down to 45 in cantabile. The hammer-string distance may be non-uniform while the aftertouch remains fixed