Pianotech

Jason

The first "phase", or resistance you feel is the damper lever engaging, (at about half way down), which is supposed to be that way. What you're hearing at this time is the damper felt moving away from the string. A kind of woosh sound, I suspect. The second "phase", is the jack escaping from the hammer butt, or, as we call it, let off. If you hit the key lightly, the hammer might not eve hit the string, or at most, just barely. 

I don't really see any "bobbling", but if the hammer is not checking on a normal blow, you might need to increase the keydip slightly to allow the jack to fully escaping from under the hammer butt. Or, you try increasing the let off distance by .5 mm.  

-------------------------------------------
Willem "Wim" Blees, RPT
Mililani, HI 96789
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Original Message:
Sent: 01-15-2014 22:49
From: Jason Gao
Subject: The weirdest bobbling I've ever encounter. Please advice.

Hi everyone!
I've encountered this bobbling situation. It's been more than 2 weeks and I've yet to find a way to eliminate this.

My let-off is adjusted according to Kawai's regulation manual (2.0mm in treble, 2.5mm in mid & 3.0mm in bass) and lost motion is adjusted so that only a very very very tiny bit of it is retained.

Jason

The first "phase", or resistance you feel is the damper lever engaging, (at about half way down), which is supposed to be that way. What you're hearing at this time is the damper felt moving away from the string. A kind of woosh sound, I suspect. The second "phase", is the jack escaping from the hammer butt, or, as we call it, let off. If you hit the key lightly, the hammer might not eve hit the string, or at most, just barely. 

I don't really see any "bobbling", but if the hammer is not checking on a normal blow, you might need to increase the keydip slightly to allow the jack to fully escaping from under the hammer butt. Or, you try increasing the let off distance by .5 mm.  

-------------------------------------------
Willem "Wim" Blees, RPT
Mililani, HI 96789
-------------------------------------------






Original Message:
Sent: 01-15-2014 22:49
From: Jason Gao
Subject: The weirdest bobbling I've ever encounter. Please advice.

Hi everyone!
I've encountered this bobbling situation. It's been more than 2 weeks and I've yet to find a way to eliminate this.

My let-off is adjusted according to Kawai's regulation manual (2.0mm in treble, 2.5mm in mid & 3.0mm in bass) and lost motion is adjusted so that only a very very very tiny bit of it is retained.

Jason,

(This is a re-posting of my message so that I can attach a photo)

The hammer buts are worn; and the bottom area where the jack contacts the butt skin has become too flat, and the jacks are in too far because the jack rest felt (hammer butt felt) has become compressed.  I have attached a screen shot picture from your video; the red circle shows the corner of the butt skin which shows that the butt skin has become flat, and the green circle shows a gap between the back part of the jack top and the butt skin, indicating that the jack is too far back.  Also, I don't know if the white stuff is powder or grease - if it is some kind of grease, that should be eliminated, it is a very bad idea.  Teflon powder here is OK, but will not solve the problem of course.

Also, two other things:

1. The letoff seems too close.  You say it is 2.5mm in the center, but it seems to be much closer, although we cannot see the tip of the hammer to be sure.

2. The damper lift is too late, which is making the problem worse.   I can see in the video that when your finger is being stopped the damper lever just barely winks.  This indicates that the damper spoon is helping to stop your finger.  Since it is timed very close to point where the jack toe touches the letoff button, you have made it want to bobble much worse.

To verify if the dampers are causing the key to stop, simply hold the damper pedal down.  If the bobbling stops or is better, then this shows that the dampers are contributing to the problem.

Solutions:

- Fix the worn hammer butts

- Set the regulation back to specifications

As a temporary test, try this test:

- remove one hammer butt

- Pull some thin flange bushing cloth under the butt skin from the side to make it round again. Trim with a sharp knife.

- Insert a long single needle through the butt felt square from the side enough times to make it thick again.

- Install the hammer butt, and regulate the capstan and letoff.  The bobbling should be gone.

If this solves the problem, then you have a couple of choices.  You can pull thin flange bushing cloth through all of the hammer butts like the same, and replace the butt felt on all hammer butts.   You should apply some glue to one side of the bushing cloth - preferable to the back side, so that it becomes glued to the underfelt, not glued to the butt skin. For the butt felt, use PVC-E or PVC-A glue to

If the butt skin is not too worn, then this might work as a repair.  If the skin is also worn, then the full repair is to remove all of the hammers at the flanges, peel off the butt skins, remove the butt felt and under felt, and replace them with the correct dimensions of new materials.  Once again, PVC-E or PVC-A glue works well.

Finally, regulation:

- Set capstans for no lost motion at all _once the hammer butts are repaired_. The jack springs are strong, and the hammer springs are weak, so during normal play the jacks will return as long as the butt skin is shaped correctly.

- Set letoff to a real 3mm in the center area.  Verify with something that is 3mm thick

- Set key dip to about 10mm, or slightly more if needed to get the jacks to clear the hammer butts. It looks in the video like the key dip is a little too deep based on the jack clearance when the key is down.

- Set damper lift to begin with the hammer 1/2 way to the strings, or a little sooner.  This forces the pianist to push their finger through the damper springs, and once they have overcome the damper spring resistance the jack springs will not be such a problem to play through.  This is the most common cause of bobbling in Kawai and Yamaha actions - late damper lift and strong damper springs.

- The low tenor damper springs are often set too strong in the factory.  From the tenor break up to about G#4 is a strong spring, and from A4 up they are more weak.  So in this section you can use a grand repetition spring tool to pull the springs back and weaken them a little - but only a little!  After weakening the springs you will most likely need to do some damper adjusting to get them to work.  Don't make them too weak!  Just slightly lighter than original.

Good luck!

Jason,

(This is a re-posting of my message so that I can attach a photo)

The hammer buts are worn; and the bottom area where the jack contacts the butt skin has become too flat, and the jacks are in too far because the jack rest felt (hammer butt felt) has become compressed.  I have attached a screen shot picture from your video; the red circle shows the corner of the butt skin which shows that the butt skin has become flat, and the green circle shows a gap between the back part of the jack top and the butt skin, indicating that the jack is too far back.  Also, I don't know if the white stuff is powder or grease - if it is some kind of grease, that should be eliminated, it is a very bad idea.  Teflon powder here is OK, but will not solve the problem of course.

Also, two other things:

1. The letoff seems too close.  You say it is 2.5mm in the center, but it seems to be much closer, although we cannot see the tip of the hammer to be sure.

2. The damper lift is too late, which is making the problem worse.   I can see in the video that when your finger is being stopped the damper lever just barely winks.  This indicates that the damper spoon is helping to stop your finger.  Since it is timed very close to point where the jack toe touches the letoff button, you have made it want to bobble much worse.

To verify if the dampers are causing the key to stop, simply hold the damper pedal down.  If the bobbling stops or is better, then this shows that the dampers are contributing to the problem.

Solutions:

- Fix the worn hammer butts

- Set the regulation back to specifications

As a temporary test, try this test:

- remove one hammer butt

- Pull some thin flange bushing cloth under the butt skin from the side to make it round again. Trim with a sharp knife.

- Insert a long single needle through the butt felt square from the side enough times to make it thick again.

- Install the hammer butt, and regulate the capstan and letoff.  The bobbling should be gone.

If this solves the problem, then you have a couple of choices.  You can pull thin flange bushing cloth through all of the hammer butts like the same, and replace the butt felt on all hammer butts.   You should apply some glue to one side of the bushing cloth - preferable to the back side, so that it becomes glued to the underfelt, not glued to the butt skin. For the butt felt, use PVC-E or PVC-A glue to

If the butt skin is not too worn, then this might work as a repair.  If the skin is also worn, then the full repair is to remove all of the hammers at the flanges, peel off the butt skins, remove the butt felt and under felt, and replace them with the correct dimensions of new materials.  Once again, PVC-E or PVC-A glue works well.

Finally, regulation:

- Set capstans for no lost motion at all _once the hammer butts are repaired_. The jack springs are strong, and the hammer springs are weak, so during normal play the jacks will return as long as the butt skin is shaped correctly.

- Set letoff to a real 3mm in the center area.  Verify with something that is 3mm thick

- Set key dip to about 10mm, or slightly more if needed to get the jacks to clear the hammer butts. It looks in the video like the key dip is a little too deep based on the jack clearance when the key is down.

- Set damper lift to begin with the hammer 1/2 way to the strings, or a little sooner.  This forces the pianist to push their finger through the damper springs, and once they have overcome the damper spring resistance the jack springs will not be such a problem to play through.  This is the most common cause of bobbling in Kawai and Yamaha actions - late damper lift and strong damper springs.

- The low tenor damper springs are often set too strong in the factory.  From the tenor break up to about G#4 is a strong spring, and from A4 up they are more weak.  So in this section you can use a grand repetition spring tool to pull the springs back and weaken them a little - but only a little!  After weakening the springs you will most likely need to do some damper adjusting to get them to work.  Don't make them too weak!  Just slightly lighter than original.

Good luck!