Key Ratio

[stanwood]

Dennis Johnson Wrote:

>Thanks David. I just did some tests with different parts but using
>the same hammer and original key ratio. I am surprised how close the
>numbers are and here is what I got for Strike ratio:

>Old Parts               5.6
>Renner early N.Y.       5.9
>Renner Hamburg          5.4

Very intersting.  How many samples did you take in each case?
(For statistically meaningful a minimum of two samples per test is required)

>I get the message that you would not automatically change an
>underleveraged key ratio.


I think you mean overleveraged.  In my work and the work of all my
associates we set the strikeWt Ratio to 5.5.  Only in special cases do we go
for a 5.0 spec.  If the action is underleveraged (high strike ratio) we
almost always
lower to a 5.5.  Sometimes we accept a 6.0 average level but we make sure to
make the hammers appropriately lighter to match.

>sort of sounds like you are consciously compensating for bad geometry with
>more leverage. Have I got it wrong?

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.

David C. Stanwood