Key Ratio

[Dennis Johnson]

        Good Morning All. First off, Bill Spurlock kindly pointed out to me
that in my original post the decimal places were all one place to the left.
I should have said 6mm, not .6mm for example. Someday I'll figure this out.


        To be absolutely sure I remeasured and recalculated all the ratios
I posted yesterday. For Strike ratio I used just two notes in the
mid-range, #27 and 49, taken with original key ratios and original leads.
For simplicity I isolated just this one section, where the key ratio is 8mm
underleveraged, and I also used the same hammer because for my purpose I
was interested in seperating the relationship of hammer weight to strike
ratio from leverage to strike ratio. Later I used a heavy hammer on full
leverage parts to compare that difference.
        I must also clarify that I understood "place temporary weights on
the back of the key so that the balance weight of key and wippen is zero"
to mean that key should balance at rest in a half-way position. This is
what I got:


Note            27              49              Average
____________________________________________________________

Old Parts       5.64            5.86            5.75  (w/old hammer 6.9g)

Renner N.Y.     6.0             6.06            6.03  (w/light hammer 6.0g)

Renner Hamburg  5.2             5.26            5.23  (w/light hammer 6.0g)

Renner Hamburg  5.2             5.2             5.20  (w/heavy hammer 8.4g)





        Imagine my surprise at the same numbers on Hamburg parts with a
2.4g heavier hammer! I am not ready draw any conclusions from this yet, but
I must stand by these numbers. Is Strike ratio more relevant to leverage
than to hammer weight?

___________

At 12:52 PM 6/21/95 -0600, stanwood wrote:

>What do you mean by "bad geometry?
>
>If you mean leverage, we compensate for that by moving capstans, etc.
>
>If you mean the relationship between coinciding arcs of the parts, first we
>make sure that spread distance is workable and the capstan contact point of
>the wippen heel is close to a straight line between the wip center and the
>key balance point.  Then we fix the strike ratio.
>



        Generally, by bad geometry I mean any deviation in the relationship
between parts from our ideal model, like you.  Here specifically, I was
referring to underleveraged key ratio, or less than .5. It is easy to
believe that one may leave slightly overleveraged keys alone, and perhaps I
did not articulate clearly yesterday.

David Stanwood wrote:

"In most cases, I set the strike weight ratio to be at an average level of
5.5.  If I can get that by choosing the right parts it makes life easier.
Otherwise I move capstans/heels in or out as needed.  This is done in about
80% of cases."


        Please correct any misunderstanding but this statement lead me to
believe that you would not automatically change underleveraged key ratios
if the strike ratio came out acceptable anyway, presumably by using Hamburg
dimension parts. Obviously, I am interested in this particular problem
because it parallels my current issue. I am not comfortable with using
Hamburg parts just to compliment or "cover up" an underleveraged
sistuation, but perhaps this is not what you meant either. These (Hamburg)
parts are not original on N.Y. Steinways, so I believe that in order to use
them you must be committed to the notion that the originals are wrong. This
is really where my concern lies.


        Thanks for bearing with me.



Dennis Johnson
St. Olaf College