Action Ratio Measurement Accuracy

[Farrell]

I am evaluating an action from a 1947 Baldwin M, prior to rebuilding. I analyzed the action ratio three different ways for each of ten notes. Needless to say, all results were not identical. The first method was a direct measurement I refer to as the Manual Action Ratio (MAR) where the key is depressed a measured distance and hammer rise is measured. A second method was Linear Action Ratio (LAR) where the lengths of lever arms are measured and the action ratio is calculated following the method outlined on Ron Over's website. The final method was based on weights and lever arms as described by Stanwood, which I will call the Component Touchweight Action Ratio (CAR). Results are below (the # before a note number means it is a black key).

Note#  MAR    LAR    CTAR
#74        5.9                   5.7
#62        5.9       5.6       5.9
#53        6.1       5.7       6.0
#31        5.8                   5.9
#14        6.0       5.4       5.9
  76        6.1                    6.1
  64        6.1       6.0       6.0
  51        6.1       5.7       6.0
  33        6.1       5.5       5.7
  16        6.0                    5.9

On average LAR values were about 6% less than MAR values, and CTAR was about 2% less than MAR. I'm disappointed they are not all closer, although it is easy for me to imagine why the LAR might be inaccurate - it is very hard to identify the exact point of contact between the capstan and wippen heel and to a lesser extent, the knuckle/rep lever contact - indeed these contacts move (I measured at about 1/2 blow position). To a small extent, the CTAR value will depend on friction as it relates to one's ability to get a real good up and down weight - as well as identifying exactly where the contact point is on the wippen heel when measuring Wippen Radius Weight. As long as one has real firm and steady measuring platforms for precise measurements, and has taken all the slop out of the action (firm rep lever, etc.) I should think the mechanical or manual method of direct action ratio would be the most accurate.

Any thoughts/opinions on this?

Terry Farrell