Strike motion ratio

[Dennis Johnson]

        I doubt that I will be in Albuquerque this summer, and I have a
question now.  I am just starting a S&S L for which I plan to do my first
complete Renner back action replacement kit. But first, this action
produces some numbers which seem to suggest contradiction with earlier
implications (regarding key ratio) or at least raise a curious problem. The
numbers are as follows:

Key Ratio =    .460

Shank Ratio = 6.753

Wip Ratio =   1.3923

Strike Motion Ratio = 4.3250

        Not impressive to say the least! Yet the Down Weight in the tenor
averages 45g, the Up Weight, 26g. Granted these old hammers are worn (the
average tenor hammer weighs 6.7g) but how does it make sense that we get
such great touch weight measurements with capstans so far off?  If I move
the capstans one full cm as required to achieve a .50 Key Ratio, they will
be completely off the cushions. What now?  My new hammers have not even
arrived yet, but I should be able to solve ratio problems by studying the
old parts. Anyway, I am using the Renner N.Y. dimension parts which
duplicate the old (with smaller knuckle).

        David, have you (or anyone else) been able yet to incorporate the
geometry of the back action into your motion ratios?  The impact of bad
geometry here must be magnified by the less leveraged shank, or is it?
Other than in these churches recently discussed with missing bass strings,
how often is the piano played with the dampers off?

        If I jumped the gun on this summer's forum, I'm sure there'll still
be plenty of fresh, virgin ground to plow.  Thanks.


Dennis Johnson
St. Olaf College