Leverage, MOI, mass, distance from fulcrum for piano key mechanism

  • Thread starter jkess114
  • Start date
  • Tags
    Piano
  • #1
jkess114
5
2
TL;DR Summary
Leverage, MOI, mass, distance from fulcrum
I am trying to determine tradeoffs in how piano keys are weighted. Piano hammer weight and the behavior of the mechanical parts in a piano action yields a spread of roughly 5:1 in leverage - every gram of weight added to the hammer adds roughly five grams at the key. Piano keys (the wooden sticks they are made of) are drilled to receive the addition of lead weights to bring the force required to play a note roughly in the 45-50 gram zone.

I have assumed its better to have less mass further from the balancing point of the key stick so the force applied to the key being closer to the weight, has less theoretical chance of initiating flex in the wooden key stick. I doubt with the forces we are talking about here if a standard keystick exhibits appreciable flex, so i am left wondering if I am missing anything else here. It seems to me, less mass further from the fulcrum is essentially the same as more mass closer to the fulcrum in behavior.

Can anyone help help the long-underserved critical thinking section in my noodle?
 
Engineering news on Phys.org
  • #2
I know nothing about piano key mechanism, but since you mentioned MOI it feels relevant to mention that adding mass further from fulcrum will result in larger MOI and I assume for a trained pianist such a key would feel heavier and probably, depending on how that mechanism work in detail, also have a longer time to return to neutral .
 
  • Like
Likes jkess114
  • #3
Moving the mass towards the fulcrum means adding more mass to achieve the same force to move the key. Does this not balance out the increased MOI of 'less weight further from the fulcrum'?
 
  • #4
Perhaps you have a diagram or sketch of the piano mechanism you have in mind, if those are not all standard?
 
  • Like
Likes berkeman and jkess114
  • #5
They are all standard. I do a lot of piano rebuilding and wind up re-weighting of keys. Its a pretty standard model.... weight at one end, finger presses at the other, lead weights installed somewhere between where the finger presses and the fulcrum. In the bass section this always means multiple weights, the number depending on where and how heavy the selected weights are.

I'm trying to understand any trade-off by having heavier weight closer to the mid point (pivot point), or lighter weight further away from the pivot point. Each method can achieve the same force required to press the key. I'd like to know if there is anything I am missing.
 
  • Like
Likes Filip Larsen
  • #6
More overall mass means more friction. This may make them feel "stickier" for the pianist, thus harder to initiate motion. Or, because friction also acts as damping, less friction may make them "bouncier" since the motion is not decelerated as much, and gives greater oscillation.

I don't know if it would be noticeable, but I know musicians (which I'm not) notice a lot of small details I don't.
 
  • Like
Likes berkeman and jkess114
  • #7
Yes, friction is a very important and very fussed-over detail when regulating or rebuilding actions, and for the very reasons you state; there is indeed a sweet spot.

In this specific case, I don't think variations in weight added to the key would change friction much as the majority of the friction in the system comes from the various mechanical connections, rotational bushings, and rubbing friction happening in the parts above the keystick, and also in the fitment of the two guide pins and mortises in each key.
 
  • #8
jack action said:
More overall mass means more friction.
You beat me to it. :smile:

jkess114 said:
I'm trying to understand any trade-off by having heavier weight closer to the mid point (pivot point), or lighter weight further away from the pivot point. Each method can achieve the same force required to press the key. I'd like to know if there is anything I am missing.
The only other thing that comes to mind is the material cost of the weights that you are adding. If the lighter weight costs half as much per weight as the heavier ones, you should start with the lighter weights to save material costs. (Although the cost of the weights may be insignificant overall.)
 
  • Like
Likes jkess114
  • #9
Thank you all for your time and energy.
 
  • Like
Likes berkeman

FAQ: Leverage, MOI, mass, distance from fulcrum for piano key mechanism

What is leverage in the context of a piano key mechanism?

Leverage refers to the mechanical advantage gained by using a lever, which in the case of a piano key mechanism, allows the force applied to the key to be amplified. This enables the action of striking the piano strings with less effort from the pianist, as the design optimizes the distance from the fulcrum and the mass of the components involved.

How does the mass of the piano key affect its performance?

The mass of the piano key plays a crucial role in its performance. A heavier key may require more force to press down, but it can also provide a more stable and controlled action. Conversely, a lighter key may allow for quicker playing but can lead to less control. The balance of mass is essential for achieving the desired touch and responsiveness in the piano action.

What is the significance of distance from the fulcrum in a piano key mechanism?

The distance from the fulcrum is significant because it determines the leverage effect. A longer distance from the fulcrum increases the mechanical advantage, allowing less force to be applied to achieve the same movement at the other end of the lever (the hammer striking the strings). This design consideration is critical for ensuring that the piano keys are responsive and easy to play.

How does the mechanical advantage of the piano key mechanism affect playability?

The mechanical advantage provided by the piano key mechanism directly impacts playability. A well-designed mechanism allows for a lighter touch, meaning that pianists can play with less effort while still achieving a wide dynamic range. This is essential for expressive playing, as it enables quick repetition and nuanced control over volume and tone.

Can the principles of leverage and mass be applied to other musical instruments?

Yes, the principles of leverage and mass can be applied to other musical instruments. Many instruments use similar mechanical principles to amplify force or control sound production. For example, string instruments use leverage in the bridge and neck to transfer string vibrations, while wind instruments rely on the mass and positioning of keys and valves to control airflow and pitch.

Similar threads

Gravity, Force and Mass Assignment, Can someone please check it?
Replies
17
Views
9K
An odd question regarding Bernoulli's Principle
Replies
5
Views
2K

Hot Threads

Recent Insights

Back
Top