Touch can be loosely described as the feel and pressure of the key moving down through it’s full cycle and back to it’s rest position. The standard for the amount of pressure it takes to push a key down is called “touchweight”.  A 50 gram weight placed on the front of the key should cause the key to slowly fall.  Not all manufacturers use this standard for “weighing off” their keys.  Touch is most easily determined on a piano which has been well regulated and adjusted.  Poorly regulated piano actions can be deceptive as well as difficult to evaluate.  It is rare to find new pianos well regulated at most dealerships.  The cheaper the piano the less likely any kind of preparation has taken place.
Find a high quality well prepared piano and play notes slowly then quickly, learning to feel how good touch should manifests itself.  Play several pianos to get a feel for differences.

The piano as a machine?  The hammer has to hit the string but how and what does that mean?  It can’t hit the string any old way. It has to be 100% accurate every time and hit the string in exactly the same place. It must have absolute precision on every strike.  All the finesse, power, dynamics, and control come from the efficiency of the machine part of the piano.  Think of the piano as a medium for transfer of power.  What the mind creates, the fingers pass along to the keys which in turn transfers energy to the piano action. The action causes the hammers to strike the string and set in motion the vibration of the soundboard which we then hear as sound.  Mental energy becomes mechanical energy which becomes sound energy which comes back to our ears and back to the mental energy of the mind upon hearing the results of playing the piano. The more efficiently this process takes place the greater percentage of transfer of power.

Touch is about the transfer of mechanical energy.
Everything comes to or off of the action rail.  This is the foundation for the whole mechanical    portion of the piano.  If this rail is out of alignment, or bends during use, every other thing coming to or from it, is compromised. What does that mean? Touch and tone will both be compromised.  1mm differences can make a big change in sound.. The key to a good action is the ability for it to maintain its precision, stability, responsiveness, and integrity for many years without needing excessive maintenance.

The biggest problem encountered by piano manufacturers is humidity. In the piano action, measurements can be as critical as a thousandth of an inch in a finely regulated concert instrument setup for a world famous artist. These instruments will be kept in a meticulously controlled environment right up to the time the performance is to take place so no changes will take place between the rehearsal and the performance. At the ISO downtown the Steinways concert grand is reregulated every time a major performer comes to town.  A 2 or 3% humidity change causes much more than a thousandth of an inch change in critical action parts.  Especially for the hammer flange and the jack. Here in Indiana humidity changes of 15 to 20% every day is common. Pianos require a lot of attention to maintain this high degree of performance capability. This is in pianos with the very best of traditional materials.  Guess what happens in lesser pianos? The alternative in the typical home instrument is to increase the “fudge factor” enough to compensate for our humidity conditions.  The trade-off is you lose the two most critical things that you have worked so hard to incorporate into the piano.  Touch and Tone.  I have worked for many years with the head piano technicians at Butler, U of I and IU and they all struggle with this same problem on their concert instruments.