Hammer position issue after hitting the string
Make another video, action in the piano, filming the hammer through the strings. Hit the key hard enough to put the problematic hammer into check, and hold it there briefly with the key fully depressed. Then just every so slightly release the key allowing the hammer to bob back up .... Do it a couple times.
Clearly I'm interested to see the repetition spring tension.
Sydney Australia
Retired part-time piano technician
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
- Edited
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
- Edited
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
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?
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