[pianotech] Bouncing Bostons

[Ed Foote]

William Monroe wrote:
> 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.............. 

Double striking?  That usually is a let-off problem, however, on a staccato blow?   I am not sure. Do we assume a1/16" let-off with a
normal drop?  What about after-touch.?
 On a simply firm blow, this could be  a checking problem, so examine the tail radius and finish as well as the back-check angle. However, 
a staccato blow, checking doesn't enter into the equation. 
    Your measurements seem to indicate that there is a pinning problem, but I don't readily see a connection.  I can imagine if the rep 
pinning was extraordinarily tight, the springs would be way too strong, thus making the hammer's behaviour odd. 
    . If the keys are overly  heavy, that can contribute, but in a cookie cutter piano like the Bostons, I wouldn't 
start with the keys.  The combination of blow with dip is strange, I would assume that there is a really low action ratio, or really heavy 
hammers.  
I think we could use some more info. 
Regards,

 

Ed Foote RPT
http://www.uk-piano.org/edfoote/index.html
 
 
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