Practical action geometry question?

[David Love]

I believe the Renner parts are designed to work with a spread somewhat less
than 4 1/2".  The old American Steinway spec was 4 3/8" (if I recall
correctly) with the German spread at 4 7/16".  I gather that this is not a
Steinway, but the Renner parts may be designed with a similar spread in
mind.  Thus, it is quite possible that the spread is too wide putting the
back of the jack window too far out and interfering with escapement.  I have
encountered similar problems.  If the wippen rail can be adjusted, I would
try it in a position where the jack is 90 degrees to the knuckle core and
see if you have clearance and proper regulation.  Check convergence lines
and capstan position under the cushion as well.

David Love


----- Original Message -----
From: "Brian Trout" <grandrestorations@yahoo.com>
To: <pianotech@ptg.org>
Sent: June 12, 2002 9:27 AM
Subject: Practical action geometry question?


Hi list,

I've been doing some reading, at least what I
could find at my fingertips, on action geometry,
and although I can find a lot of general stuff,
and a lot of theory, specifics aren't quite as
easy.

I've changed out the wippens and
shanks/flanges/knuckles on a well known action.
The new parts are Renner and are the closest I
could get to original dimensions.  However, they
are NOT identical.

The wippens are shorter in length by about 3mm,
the variation appearing to be mostly out at the
jack end of the wippen. When I leave the action
spread at 4 1/2", as was the original, the jack
doesn't have room to clear the knuckle before it
burys itself in the felt stop at the end of the
wippen.

I can't seem to get a picture in my head of the
negative effects of shortening the action spread,
or if I'm doing anything wrong at all.  It's been
drilled into us tech types that the action spread
is sacred and NEVER to be messed with.  Well, I
had to do something, 'cause the way it was, it
wouldn't work, period.

What has seemed to work in this instance is
moving the hammer rail forward about 3mm.
(Another possibility would have been redrilling
the hammer rail to put the flanges a few mm
farther back <towards the back of the keys>). I
just wanted to run it past someone else who might
have seen this stuff before just in case I'm
overlooking a disaster looming on the horizon.

Any insight?

Thanks,

Brian T.


=====
Brian Trout
Grand Restorations
3090 Gause Blvd., #202
Slidell, LA  70461
985-649-2700
GrandRestorations@yahoo.com

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