Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum Relationship between key dip and damper lever rise

Something that I've been wondering about for some time, and has resurfaced due to regulating my Kawai grand. How do you maintain consistent damper rise at the back end of the key with the naturals and the sharps, while having the same key dip?

Here's what I think I know...

1. The height of the damper lever cushion or back end of the key in the rest position is dictated by the back rail felt and nothing else. So regardless of how the action is regulated, the back end of the keys will always be level assuming the felt is in good condition.

2. Key height does not affect the rise of the damper cushion on key press. The rise of the damper cushion is purely dependent on key dip.

3. On my Kawai, the distance between the balance rail pin and the front end of the key is 2x the distance between the balance rail pin and the center of the capstan. This is true for the sharps as well, because although the key length is shorter, the balance rail pin is offset from the naturals such that this 2:1 is maintained with the capstans.

So my question then becomes...

Assuming a standard key dip of 10 mm for the naturals, the capstans on the naturals will rise 5 mm because of the 2:1 lever. The damper cushion will rise a proportional amount, based on the distance from the balance rail pin to the damper lever cushion.

Now for the sharps, a key dip of 10 mm is also required so that the action is consistent. Because the ratio is also 2:1 as described above, so the capstans for the sharps will also push the wippens up by 5 mm.

BUT...the ratio between the damper cushion to the balance rail pin, and the balance rail pin to the front end of the key is not the same between the naturals and the sharps. Therefore with a consistent 10 km key dip, would the damper cushions of the sharps not rise more than the naturals?

I hope I'm not missing something blatantly obvious, but the trigonometry seems to suggest that you can't achieve consistent key dip and damper cushion rise simultaneously; something has to be sacrificed.

Would appreciate it if anyone can shed some light on this for me.

You are correct. The rise of the key end felts of the sharps is slightly greater than for the naturals. This is why the damper up-stop rail is set to allow for more free play on the naturals than the sharps. Also, the damper pedal stop should be coincident with the damper levers up-stop rail setting.

Hi Phillip,

The question is a matter of tolerance. The damper timing is not that sensitive, IMHO. It should be between 1/3 and 1/2 the blow distance. I have not heard any technicians claim an improvement in responsiveness with a consistent damper timing within a smaller window.

However, some grands I've seen do have tiny spoons that are bendable or tiny buttons that look like let-off buttons. These allow for individual damper lift timing but they are not popular.

(I don't have as extensive an experience with grands as some others on this forum. Comments?)