I often read questions on piano technician forums from technicians asking how to regulate a specific piano. For example, recently someone posted this.
“I’m regulating a piano and the book says to regulate blow distance at 1.5 inches”
or
“I can’t find any regulation specs for this specific piano in any books”
The writing of these books implies that each piano requires a specific set of regulation adjustments and if one were to set these adjustments exactly as the book states, then the piano would be performing at its highest level possible.
Wear of the parts means that these specs might not work as intended.
Also, indicating a specific specification for key dip ignores the fact that some pianists prefer less key dip. The skilled technician knows how to adjust all the regulation specs so that the pianist can get what they want.
Key dip, blow distance, and let off all work together to give the best after touch. Descriptions and the starting point for these settings are given below. The sensitivity refers to the tolerance of the settings, i.e. how important it is that these settings are close to the dimensions given.
Key Dip. How much the key travels from the top rest position to the bottom of the key bed. Standard setting is 3/8″ – 7/16″ (9.5mm – 11mm). Moderate sensitivity.
Blow Distance. This is how far the hammer travels from rest position to the strings. Standard setting for this is 1 7/8″ (48mm). Low sensitivity.
Let Off. This is the distance that the hammer is from the string at the moment of let off. Let off is when the jack toe engages with the jack button and the jack top begins to move out from under the hammer butt. Standard setting for let off is 1/8″ (3mm) for uprights and 1/16″ (1.5mm) for grands. High sensitivity.
After Touch. This is the most critical setting for pianists. They can feel when it’s off, even if they don’t know what it is or they can’t explain what’s wrong with the feel. It is described as the distance that the key travels from the moment the jack starts moving out from under the hammer butt (let off) and the bottom of the key bed. Typical distances are 0.040″ – 0.060″ (1mm – 1.5mm).
Here’s the thing. After touch can remain the same if you change two other settings. Another way to describe this is to say, “We can change one setting and then change another setting so that the aftertouch remains the same.”
A common reason to want to do this is to produce less key dip as per a request from a customer. Specifically, you could reduce the key dip but follow with reducing the blow distance and the result would be no change in aftertouch, no change in feel except that the note plays with less key dip. You could also increase let off.
The choice of which settings to adjust depends on the sensitivity of the setting and what it is at. For example, in the example above, if the let off was so small that the hammers were blocking or double striking, you would choose to increase the let off before adjusting the blow distance.
If you would like to learn more about how to know what settings to change in order to change after touch or keep it the same, look up The Regulation Triangle. It describes a simple way to know how to regulate a piano without having to look up settings in a book. This technique works for all pianos.