Josephine I thought the drop is what happens after hitting the strings. But maybe I'm wrong. I thought what happens before is called let off.

Correct. "Let off" is the jack being pushed out from underneath the knuckle (the round leather cylinder on the hammer shank) just prior to the hammer striking the strings as it moves upward (around 1.5-2 mm from the strings). At the very same time (in a well regulated grand piano) the repetition lever (the other bit sitting under the knuckle) contacts its stop adjustment. As the piano key continues to be pushed down past these 2 contact points the repetition lever 'drops' (typically about the same distance again as let-off). Now the hammer is sitting around 4 mm from the strings (let-off plus drop). Then as the key is pushed to the very end of its travel the hammer again starts to rise. But it doesn't rise sufficiently to 'bobble' against the strings (assuming let-off, drop, and after-touch are correctly adjusted).

Clear as mud.


Sydney Australia
Retired part-time piano technician

      AlvinC Hi John, noted. What you descrip is the way to check the spring tension. I did tried so but no video was filmed. I will make the video per your instruction within this week and let you know then.

      Hi Alvin,
      Just be aware I'm 'on the road' for an indefinite time so may be slow to respond to your video (hate using my mobile phone for this sort of stuff). What you are looking for is the speed the hammer rises from check when released by taking pressure of the key. It should rise as what is often said "at the speed a normal person rises from sitting in a chair".

      If the repetition spring is set too strong it fights the hammer rebounding back into check. If it leaps up, it is set to strong. Also check the hammer tail and see if it has become polished and smooth where it contacts the back check leather. Taking any shine off the timber tail with just an ever so light rub with a modest grit sandpaper can make a big difference. Just remove the shine, no more.

      Sydney Australia
      Retired part-time piano technician

          JohnCW

          Do you think it's a good idea to turn the drop screw a little bit to see if this fixes the problem of AlvinC's piano? (I'm asking because I want to learn from this, if the first video is made after playing the note the hammer looks too close to the strings).

              Josephine Do you think it's a good idea to turn the drop screw a little bit to see if this fixes the problem of AlvinC's piano?

              No. That's just adjusting things willy-nilly. To do the job right, everything needs to be adjusted correctly. But the staring point is having a somewhat correct repetition spring tension. And as an overly strong repetition spring is one of the main reasons for the hammer not checking on a soft blow, the best place is to start there.

              I'm assuming the back-check itself is set close to correct as in the video the two hammers checked in a near identical place on a firmer blow.

              Sydney Australia
              Retired part-time piano technician

                  JohnCW

                  Thanks for explaining!

                    JohnCW Hey John, no problem as I am not in urgent need to restore it correctly. I guess the hammer tail is fine as I switched the OK hammer to this problematic key for test and sadly the problem does not disappear.
                    Happy and safe trip!

                      Josephine Hi Josephine, correct me if I am wrong since I am not a technician and only a piano fan. But I am indeed interested in learning regulation as I can understand much better of the piano I play.

                          AlvinC

                          I'm not a technician either, I just like to learn about pianos πŸ™‚

                            JohnCW
                            Hi John, when you are available could you help to check the spring of below? the first hammer is the problematic one and it needs really heavy velocity to set on check
                            [

                              Repetition spring is to strong. It needs to be weakened to remove that bounce at the top of the hammers travel (which I assume you should be able to feel through the key).

                              I believe you said you had previously adjusted it so I assume you know how to do this and have the tool to hook the butterfly spring in and out.

                              Sydney Australia
                              Retired part-time piano technician

                                To pinpoint the location of the problem, would it be a good idea to just swap hammers or wippens with the neighbor key and see if the problem has shifted to the new key?

                                  Rubens Hi Rubens, I did swap the hammers earlier and the problem still exists in the problematic key.

                                      AlvinC Ah, so it's almost certainly something in the wippen.

                                          JohnCW Hi John, thank you for the prompt response. what about the spring of the other two keys shown in the video? it's not easy for me to tell which one is too strong by watching its speed

                                              AlvinC Just assess the rise speed of each hammers when released from check. As I mentioned in a previous post they should rise about the speed someone gets up from a chair, with no kick/bounce at the top of their travel, and no kick should be felt through the keys.

                                              Sydney Australia
                                              Retired part-time piano technician

                                                  Rubens Yes, now I just need to test whether adjust on the repetition spring can help. Thanks.

                                                    JohnCW Thanks, John. I will try to adjust and keep all of you posted later.

                                                        AlvinC If you're going to try adjusting the repetition spring do yourself a favour and buy the Hart Spring Tool. It is considered the best going for hooking out those pesky butterfly springs.

                                                        Now you might think it's overkill just to adjust one spring. But look at it this way, there are bound to be more among the other 87 that need adjusting.

                                                        Sydney Australia
                                                        Retired part-time piano technician

                                                            JohnCW Dear John, thank you so much for making the regulation look like more desperately. Just kidding. I do respect every technician, the regulation is really time-comsuming and tedious. I am new to this forum and regulation and so grateful to have all your generous and friendly replies.
                                                            BTW, I did try to lower the tension of the spring with tool in the weekend. It improved but still the problematic key takes harder blow to be checked by the backcheck (see below video). So I just want to know what is the standard velocity for the hammer to be checked? I always worry to set the spring strength too low or damage the spring.
                                                            [

                                                                AlvinC Repetition spring is still to strong. If you excessively weaken it by bending it simply won't push the hammer up out of check when you release pressure on the key.
                                                                It needs to rise without that clear bounce/kick at the end of its upward travel when released from check.

                                                                Sydney Australia
                                                                Retired part-time piano technician