Have you checked the back check angle and height? On a staccato blow, I have had the back of the hammer felt catch on the top of the back check then release.
Al -
High Point, NC
From: William Monroe
Sent: Thursday, July 29, 2010 11:32 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] Bouncing Bostons
Yeah,
It's not double striking like Let-off/drop bobbling. On a firm Stacatto, I can watch the hammer "bounce back" from what appears to be rest position - checking really is not coming into play and neither would I see a reason to suspect the tail shape. Leading pattern in the keys is pretty normal 3 and a half in the bass, tapering up evenly. Yes, about 1/16" let-off, about 1/16" drop. After touch was huge prior to me regulating it (key travel was around .430" - yes, really), and the problem didn't change when the regulation specs were changed. There is some aftertouch, but not excessive - some rise, but certainly not back to the strings.
Ed, why do you think 1 3/4" and .400" is markedly out of the normal range? Just curious. I find that this amount of key travel is on the wider side, but still workable with 1 3/4" blow in a lot of actions. Didn't get to measure the action ratio or strike weights.
William R. Monroe
On Thu, Jul 29, 2010 at 9:20 PM, Ed Foote <a440a at aol.com> wrote:
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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