Piano actions have not changed in over one hundred years. So why would there be a need for action analysis? It’s because the tolerances of an action are so tight that small variances can make a big difference on the performance of an action. In our modern age of technology how do these discrepancies occur? It’s because pianos are mostly made of wood and wood by its nature is an inconsistent material. Manufacturers have developed techniques to work around these inconsistencies by providing points during manufacturing to correct tolorances. In ultra modern factories these tolorences can remain quite small. Smaller manufacturers and manufacturers from the past use much more hand work and the variances can add up to big changes from piano to piano. What this means to the rebuilder is that the same model piano can be quite different from one to the next. Assuming a manufacturer’s current parts will fit a vintage early American piano is what got many rebuilders from the 70’s and 80’s into trouble. They would do their best to put all the parts together, only to find the piano would not play as well as before they started. No amount of regulation could correct the problem. Fortunately, the understanding of these principles has increased tremendously in the last twenty years.
My method of action analysis is to use a multi–system approach. This involves both computer analysis and empirical investigation. I begin by taking very accurate measurements of the original action. This includes the layout of the action parts, the key height, both front and back, string heights throughout the scale, center pin heights, action to damper underlever relationship, various weight measurements, and any other measurements that might be necessary. The picture shows the action geometry program that I use. Its useful for giving me a point of reference for the old action as well as how the new parts should perform.
My other method is to physically try new parts on the existing action frame using all currently available parts. This is the most reliable way to select new parts. What you see is what you get. Sometimes however, problems exist that cannot be corrected with part selection alone. For this I use a custom built action model to test various aspects of the action geometry. This action model allows me to change every parameter in an action including key ratio.
There are other methods available to analyze action geometry, but I always start with these systems first.