[pianotech] double-striking hammers on Chinese uprights

[Paul McCloud]

With the Schwander type of hammer spring, the letoff distance can be
increased because of the weaker spring rate.  There's plenty of momentum to
allow the hammer to get to the string, and making the adjustment will help
the backcheck do its job.  I had a shipment of pianos which had a very
pronounced bobbling problem.  Making the letoff at about 1/4" made most of
the problems go away.  YMMV.
	Paul McCloud
	San Diego


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Jim Busby
Sent: Wednesday, August 19, 2009 4:53 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] double-striking hammers on Chinese uprights

All,

Can I throw something else into the mix? Last year I posted a similar
problem on CAUT and got a lot of the same advice. Lot's of good advice,
great advice, for the "normal" or typical resolution of double striking.
However, nothing solved it completely. 

It was the same make as Britney's piano, and I tried everything. The real
problem seemed to be in the design, or at least the implementation of it,
whether right or wrong. (i.e. The design may have been good but the
gorrillas in the factory missed it.) If the hammer assembly doesn't tend to
"lean" (for lack of a better word) back so that the center of gravity favors
a return, it sometimes ends up double bouncing more. The Chinese pianos use
the Schwander type return spring, which is considerably less strong than the
American spring. The weaker spring can't overcome too much of this gravity
thing. If the hammer isn't raked enough, and/or if the hammer
assembly/action (balance) set up is not favoring a return this problem seems
to be exacerbated. On my piano strengthening the return spring helped, but
there was something else.

With my piano I experimented by physically leaning the piano forward (toward
the player, slightly) and the problem went away. So... what I ended up doing
is "Turbocharging" the piano a la Jack Wyatt. I won't post this exact
procedure here since Jack might not like that, but maybe it's been posted
before. It consists of tilting the action forward (out, spacer washers) then
reregulating blow, etc. 

FWIW, that's what did it in my case..

Jim Busby=
No virus found in this incoming message.
Checked by AVG - www.avg.com 
Version: 8.5.392 / Virus Database: 270.13.52/2298 - Release Date: 08/19/09
06:03:00