geometry/friction

[stanwood]

>>Another factor to consider is effeciency of the coinciding arcs:

>>2. The knuckle/jack contact point is purposefully out of align to create
>>ineffeciency which expresses itself as friction which is built in for a
>>feeling of control.  If the spread distance and orientation is normal the
>>above figures will work best as QUIDELINES.

>If this bit of geometric detail regarding the knuckle/jack contact point is
>so brilliant, than why are we compelled to be so liberal with the dry
>teflon powder?

>I suggest it is because the heavier parts on modern pianos have created a
>problem where previously none existed.

>Dennis Johnson

Dennis,

There have been problems for a long time.  If you read Paderewski's (sp?)
memoirs he relates how he had a problem with heavy Steinway actions and he
seriously injured himself on a Steinway.

Last weekend I completed a 1902 Mason & Hamlin CC (9' 4 1/2")action with new
Renner parts.

Here was the situation:

1.Strike weights all in the high zone.
2.Rotational hammer flange friction set precisely 4.0 grams by the guage.
3.Wip centers friction averaged around 4.0 grams as well.
4.I dry lubed the key pins and made sure that key bushing friction was minimal
  (no more than 2.0 grams throughout).
5.The capstan/heel contact was very close to the WipCenter-BalanceRail line
at   half stroke for both the sharps and the naturals.
6.Shanks were just off the cushions at 1 3/4" blow
7.Action Spread 4 13/32"

The Friction Weight (Down-Up)/2 turned out to be roughly 20.0 in the bass
running down to 15.0 in the treble.  I determined the average ratio to be 6.0

I moved the capstan line in towards the balance rail by 0.150" and modified
the heel so as to stay close to the straight line rule.

I remeasured the friction and found it had changed from an average of 14.0
grams in the bass to 10.0 grams in the treble.  The strike ratio averaged
out to 5.1 which is what I was aiming for.  The keys were leaded to the 5.1
ratio.

I did not need to dry lube the knuckles.  I prefer not to because it wears
off with time.  The system can always be made to work without dry lubing the
knuckles.

This demonstrates very clearly that if your strike weights are in the high
zone ratio very easily becomes a negative factor if it's too high.  I could
also have corrected the problem by reducing the strike weight but I did not
consider that an option as this was a piano going into a concert hall.

Oh I almost forgot!!  I did play the piano before and after.  It felt a
little stiff before moving the capstans.  Afterwards it felt just right.

By the way when I first started moving capstan/heel lines it was alot of
work and time.  But after having done it many times I've gotten into a
routine which makes it a very efficient operation to carry out.  In great to
have the option to change ratio when the situation demands it.  In this
situation everything seemed right except the strike ratio and changing that
remedied the friction problem.

David C. Stanwood


Here is a copy of a similar experience that I posted last June:
--------------------------------------------------------------------------------
Date: Thu, 29 Jun 1995 17:18:06 -0400
From: stanwood@tiac.net (stanwood)
To: pianotech@byu.edu
Subject: Friction/StrikeRatio

I've been thinking about the recent discussion on reducing friction with
small knuckles.  I've noticed that changing the ratio by moving the
capstan-heel position also changes friction.

The data below shows FrictionWt as (DownWt-UpWt)/2
Before and after moving the capstans and heels
approximately .375" to change strike ratio from an average
level of 7.5 to 5.5

The data is from a model D #51428 at Harvard University

Note     7.5      5.5        Friction difference

  1     18.5     11.5            7.0
  2     23.5     16.0            7.5
 16     26.0     12.0           14.0
 17     21.0     11.5            9.5
 28     18.5     10.5            8.0
 29     14.5      9.0            5.5
 40     18.5     10.0            8.5
 41     15.5     10.0            5.5
 52     13.0      8.5            4.5
 53     18.5     12.0            6.5
 64     18.5     12.5            6.0
 65     16.5     11.5            5.0
 76     13.5      9.5            4.0
 77     14.5     10.5            4.0
 85     13.0      7.0            6.0
 86     14.0     11.0            3.0



In the above example, nothing was done other that moving the capstan line.
NO other friction work was done.  Moving the capstans killed two birds.
The friction and the ratio both were corrected.

David C. Stanwood
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