Back rail and key leads

[V T]

Hello Paul,

Regarding the back rail cloth:

I recall that the piano is 9' long with tapered length
keys.  Is the key height measured at the front of the
keys uniform from 1 to 88?  Is the existing action
cloth more or less centered under the back checks and
therefore at an angle to the front edge of the keys?

I am puzzled that the capstan on key 1 never reaches
the ideal line between the key fulcrum point and the
wippen center.  Since the hammers seem to be worn, if
anything, I would expect the capstans to be raised to
compensate for the hammer wear, and yet the symptom
you describe indicates either that the capstan is too
low, or that there aren't enough punchings on the
balance rail.

If you can, you could also do some detective work and
figure out what all was done to the piano since it
left the factory.  Often, the problems are caused when
"repairs" are done.  For example, was lead added to
the action after it left the factory, or do all the
leads look like original equipment?  Did someone
replace the hammers with ones of wrong hammer bore
distance?

Regarding the weight problem, normally, a piano will
have around 14 grams of friction weight in the bass,
and less than 10 g in the treble.  The friction is
calculated from (DW-UW)/2.  This is the force required
to overcome the action friction when pressing down on
the key.

The other number that is way off on this action is the
balance weight, which should be around 35-38g. 
BW=(DW+UW)/2.

In theory, you can install light hammers and remove
lead, but you do need significant weight in the
hammers for a piano that size.  I would therefore
measure the strike weights of the hammers and see
where they fit on  David Stanwood's curves.  If you
aren't familiar with this subject, he has some papers
on his web site and some older PTG Journals have them
too.  In a nutshell, you adjust the hammer weight to
match the piano size, the action ratio, and the
desired balance weight and inertia of the action.  The
subject can get more complex if you aren't happy with
the action geometry, but I will assume that piano was
in acceptable working order at one time, and that you
don't need to redesign the action.

Anyway, I would check the key height from 1 to 88
first and solve that problem before dealing with the
weight.

Best regards,

Vladan

=================================================

Thanks for the reply Vladan.  It is nice to share my
thoughts with someone
else.

Regarding the backrail cloth....
There should be a straight line from the bottom of the
key at the balance
rail pin to the center pin of the wippon where, when
the key is depressed
half way, the top of the capstan should be.  I get
that on 88, but not on 1.
On 1 the key would have to be more than fully
depressed for the capstan to
make this line.  And it tapers up to 88.  If nothing
else, shouldn't there
be some consistancy?  Or, doesn't this matter?  Are
the capstans in the
wrong place?

Because of this, I'm wondering if there was some
compensation somewhere else
(like excessive leading) to make up for this.

Regarding the weight....
I assume that the 7 grams you are referring to is an
estimate of the amount
to move the new parts, correct?  And.... Doesn't it
make sense to maintain
the existing hammer weight and reduce the weight in
the key to increase the
down weight and corresponding up weight reducing the
overall inertia of the
action?

Paul.


		
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