Pianotech

Shafer & Sons studio upright "relatively new", high gloss finish.  Bobbling hammers in the tenor section and just into the treble section, but WHITE keys only (maybe a dozen or so).  No excessive lost motion.  Keys level.  Hammer blow and let off consistent throughout.  When observing the action alongside the black (non-bobbling) keys, it appeared that the hammers were checking too late (if at all), allowing the butt to bounce on the jack.  Backchecks were all still in the factory positions.  Since the adjacent black keys were all performing well, (as well as other white keys outside the affected section) and no other problem was apparent, my conclusion was that the butt leather and/or back check felt on these white keys has been worn down over the years (four children and one adult player daily over the past 15+ years).  I was able to temporarily eliminate the bobbling by adjusting the back checks on the affected keys, but who knows how long that may last.

Three questions: 

1)  Am I missing/forgetting anything?  (Usually I've solved this issue on uprights by eliminating excessive lost motion, but that's been on "lesser-used" pianos.)

2)   What (if any) remedies may be attempted short of replacing butt leather or back check felt?

3)   Any suggestions for "shortcuts" or techniques to shorten labor time in replacing these felts/leathers?  (About a dozen or so at this time.)

Thanks. 

--- Tim

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Timothy Edwards
Beckley WV
(740) 517-7636
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You can try brushing the catcher leathers (ecsaine) and catcher felt with a stiff brush.

Replacing a dozen of the leathers wouldn't take long if you use Ca glue. You could do it in the home. Precut strips help. 

Check the butt leathers for excessive wear while your at it.

Sounds like these folks like the white keys a lot more than the black ones, if the key height is even a little low in that area bringing it up will help. Compare to notes at the top and bottom of the keyboard.

Adjusting the back checks to compensate for wear is a legitimate repair. 

These are Pearl River pianos btw.

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Steven Rosenthal RPT
Honolulu HI
(808) 521-7129
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When I run into this, I reach for my key dip block.  13/32 inches is 10.3mm.  I expect to find the dip shallow, most likely because the balance rail cloth punching has compressed.  My solution is to shim up the balance rail with card stock.  I consider this expected maintenance in the first few  years of a piano's life.

I also concur with the comment above about brushing the catcher leathers.

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Floyd Gadd RPT
Regina SK
(306) 502-9103
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Original Message:
Sent: 04-14-2024 21:09
From: Steven Rosenthal
Subject: Bobbling hammers

You can try brushing the catcher leathers (ecsaine) and catcher felt with a stiff brush.

Replacing a dozen of the leathers wouldn't take long if you use Ca glue. You could do it in the home. Precut strips help. 

Check the butt leathers for excessive wear while your at it.

Sounds like these folks like the white keys a lot more than the black ones, if the key height is even a little low in that area bringing it up will help. Compare to notes at the top and bottom of the keyboard.

Adjusting the back checks to compensate for wear is a legitimate repair. 

These are Pearl River pianos btw.

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Steven Rosenthal RPT
Honolulu HI
(808) 521-7129
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Floyd, If the sharps are not a problem then raising the balance rail might create too much aftertouch in the sharps.  Lowering natural's dip might fix the problem, but if sharps are OK then he might need to search for another issue, though I don't see anything obvious from this meager information.

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Blaine Hebert RPT
Duarte CA
(626) 390-0512
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Original Message:
Sent: 04-14-2024 21:36
From: Floyd Gadd
Subject: Bobbling hammers

When I run into this, I reach for my key dip block.  13/32 inches is 10.3mm.  I expect to find the dip shallow, most likely because the balance rail cloth punching has compressed.  My solution is to shim up the balance rail with card stock.  I consider this expected maintenance in the first few  years of a piano's life.

I also concur with the comment above about brushing the catcher leathers.

------------------------------
Floyd Gadd RPT
Regina SK
(306) 502-9103
------------------------------


Original Message:
Sent: 04-14-2024 21:09
From: Steven Rosenthal
Subject: Bobbling hammers

You can try brushing the catcher leathers (ecsaine) and catcher felt with a stiff brush.

Replacing a dozen of the leathers wouldn't take long if you use Ca glue. You could do it in the home. Precut strips help. 

Check the butt leathers for excessive wear while your at it.

Sounds like these folks like the white keys a lot more than the black ones, if the key height is even a little low in that area bringing it up will help. Compare to notes at the top and bottom of the keyboard.

Adjusting the back checks to compensate for wear is a legitimate repair. 

These are Pearl River pianos btw.

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Steven Rosenthal RPT
Honolulu HI
(808) 521-7129

Bobbling hammers can be caused by several things. In my experience, the top two culprits are not enough aftertouch and too much lost motion. If your lost motion is correct, try increasing aftertouch and see if that fixes your problem. 

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Benjamin Sanchez, RPT
Piano Technician / Artisan
(256) 947-9999
www.professional-piano-services.com
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In some of the Chinese pianos, the damper springs were/are very firm.  On a soft blow, this may also cause the hammers to bobble.  This is because the velocity of the keys is slowed when the spoon hits the damper lever.  Playing firmly usually stops the bobbling.  If the damper springs are too strong, you can weaken them somewhat and see if that helps.  I usually use the Hart spring tool, and simply pull back on the spring to weaken it.  If the other suggestions don't seem to work, you might look at the damper spring tension.

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Paul McCloud, RPT
Accutone Piano Service
www.AccutonePianoService.com
pavadasa@gmail.com
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Point well taken Blaine.  I would add that before I would shim the balance rail, I would evaluate the checking of both naturals and sharps.  If I am confident that the back checks are in their factory position, and there are situations where that is the case, and the sharps are checking too far back from the strings, even if there is no bobbling, I do consider the sharps to be a problem, along with the naturals.

Comparing wippen position at full dip will also give me insight as to whether there is something out of whack between the dip of the sharps and the dip of the naturals.

Again, glazing of the catcher leathers needs to be dealt with if it is present, and as Paul pointed out just above, the strength of the damper springs matters.  I purchased a tool some years ago from Keith Bowman that facilitates both the evaluation and the adjustment of the spring tension.  I see Renner USA now carries it under the name Upright Damper Spring Tension Tool.  I find this to be a valuable tool.

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Floyd Gadd RPT
Regina SK
(306) 502-9103
------------------------------

Original Message:
Sent: 04-15-2024 00:05
From: Paul McCloud
Subject: Bobbling hammers

In some of the Chinese pianos, the damper springs were/are very firm.  On a soft blow, this may also cause the hammers to bobble.  This is because the velocity of the keys is slowed when the spoon hits the damper lever.  Playing firmly usually stops the bobbling.  If the damper springs are too strong, you can weaken them somewhat and see if that helps.  I usually use the Hart spring tool, and simply pull back on the spring to weaken it.  If the other suggestions don't seem to work, you might look at the damper spring tension.

------------------------------
Paul McCloud, RPT
Accutone Piano Service
www.AccutonePianoService.com
pavadasa@gmail.com
------------------------------

Original Message:
Sent: 4/15/2024 8:27:00 AM
From: Floyd Gadd
Subject: RE: Bobbling hammers

Point well taken Blaine.  I would add that before I would shim the balance rail, I would evaluate the checking of both naturals and sharps.  If I am confident that the back checks are in their factory position, and there are situations where that is the case, and the sharps are checking too far back from the strings, even if there is no bobbling, I do consider the sharps to be a problem, along with the naturals.

Comparing wippen position at full dip will also give me insight as to whether there is something out of whack between the dip of the sharps and the dip of the naturals.

Again, glazing of the catcher leathers needs to be dealt with if it is present, and as Paul pointed out just above, the strength of the damper springs matters.  I purchased a tool some years ago from Keith Bowman that facilitates both the evaluation and the adjustment of the spring tension.  I see Renner USA now carries it under the name Upright Damper Spring Tension Tool.  I find this to be a valuable tool.

------------------------------
Floyd Gadd RPT
Regina SK
(306) 502-9103
------------------------------