[pianotech] Bouncing Bostons

[Tony Caught]

 Not sure if it has been mentioned but the backcheck angle can cause this
problem. Make sure that the hammer tail and the backcheck are gripping then
freeing on a staccato  touch. It is possible for the hammer tail to return
to the top of the backcheck, bounce off and strike the string. A slightly
greater angle on the backcheck should solve that problem

 

 

Tony Caught

acaught at internode.on.net

 

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Don Mannino
Sent: Saturday, 31 July 2010 12:44 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] Bouncing Bostons

 

William,

 

A few thoughts if I may, since the basic specs in the Boston action are the
same as the Kawai:

 

-          Dip of .400 is pretty much the same as normal 10.2mm spec, so
that’s fine.

-          Blow of 46mm is normal

-          Key balance hole is probably too loose, allowing the key (and
it’s lead weights) to bounce up off the balance rail. This bounce can
coincide nicely with the return of the hammer, sending it back up with more
energy than the hammer alone.  To test this, place a finger firmly on the
key button just behind the balance pin and do the Staccato blow.  If this
reduces the hammer bounce, you have a solution.  Make the balance hole
tighter, so that is will SLOWLY drop back to rest position instead of freely
falling.

-          Balance rail bedding keyframe should be rechecked as well

-          Hammer rest felt should be about ½ the hammer shank thickness, so
you may have it correct already.

-          Hard back rail cloth could contribute.

-          Very loose hammer centers might contribute as well, but I
wouldn’t consider that the prime cause.

 

As Ron said, if one tries to make an action do this, one can usually make it
happen.  But it really shouldn’t show up when playing music.  Check the
balance rail holes – that’s my best guess as to the primary problem, and set
the hammer line a little lower along with resetting the hammer rest
(rebound) rail to match.

 

Don Mannino

 

 

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of William Monroe
Sent: Thursday, July 29, 2010 6:20 PM
To: pianotech at ptg.org
Subject: [pianotech] Bouncing Bostons

 

Hi List,

 

Anyone know of anything chronic in Boston Grands (GP178) that has the hammer
double striking on a quick/firm staccato blow?  I've got one that does.
Anyone have any ideas/solutions?  The piano is finely regulated otherwise
(just today, in fact).  1 3/4" blow, about .400" Key Travel, Checking about
1/2", Rep springs are definitely NOT jumpy.  In all other ways, the action
plays nicely, controllably.  And that is no mean feat.  I took some DW/UW
measures today out of curiousity, and they were haywire.  DW range from 62g
- 46g, UW from 18g to 35g or so.

 

My thoughts are turning to action pinning (haven't checked yet).  Key
Bushings and pins are clean and lubed (teflon), but that's as far as we got.
Wondering if tight pinning (of any parts) might contribute to this
rebounding back into the strings - and it is a full rebound.  You can watch
the hammer appear to bounce off the rest rail, though I'm not convinced that
is exactly what is happening.  Kind of musing aloud here.............. 


William R. Monroe

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