Leverage and Dip

[David Love]

For any action ratio there is a given relationship between dip and blow.
The action ratio not only refers to the relationship between change in
weight at the hammer and the resultant change in weight at the key, it also
refers to the relationship between key travel and hammer travel.  A quick
way to calculate the action ratio is by measuring how far the hammer travels
for a given amount of key travel.  The complication arises when you put the
let off button in the way.  At a ratio of 6:1, for example, 10 mm of dip
will result in the hammer traveling a total of 60 mm.  (It also means that a
change in 1 gram at the key will result in a change of 6 grams in the
balance weight.)  Sixty mm seems like much more than you need, but remember
that the travel of the hammer is interrupted by let-off.  The key travels
through let off and aftertouch while the hammer travel is interrupted.  The
formula that would be useful to you is:

(Blow Distance - Letoff) / (Key Dip - Aftertouch) = action ratio

Working backwards you can figure out the basic parameters for a given key
dip from an established action ratio.

My general method these days is to target a specific action ratio (or strike
weight ratio if you prefer) which gives me the regulation that I want.  I
find the ideal to be 5.75.  From there you can calculate the strike weight,
front weight, balance weight curve using algebraic manipulation of
Stanwood's formulas.  On a concert grand that requires additional blow
distance, the ratio must be increased a bit to get additional travel if you
don't want the dip any deeper.  This is a bit ironic since the general trend
is to use a heavier hammer on a concert instrument.  This forces you to push
the key leading up a little bit if you want to go that route (or use assist
springs).  The other alternative would be to lower the action ratio and use
a deeper dip.  I'm not sold on the need for heavier hammers so I tend to
abide by the desired ratio and go from there.

David Love



----- Original Message -----
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: "PTG" <pianotech@ptg.org>
Sent: October 02, 2002 2:27 PM
Subject: Leverage and Dip


Hi folks

Ran into a question I couldnt answer precisely the other
day, and as it was actually an interesting question I
thought I would pose it to you all.

If you decide to bind yourself to exactly a 10 mm dip in a
grand action set up, what degree of freedom is left to you
concerning how much leverage you can select and still have
the action operating inside reasonable parameters ?

Obviously you can fudge a bit with strike distance, letoff
and drop to push your leverage in as much as you can get
away with... but just how much exactly CAN you get away with
?

In other words... given a 10 mm dip..... what are the
highest and lowest total action ratios you can end up with?

Cheers !

RicB

--
Richard Brekne
RPT, N.P.T.F.
UiB, Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html


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