Posts tagged rotational inertia

Piano Touch Weight

When you ask a child to draw a picture of a car, invariably it looks like this – wheels (with spokes hahaa), windows (again with panes lol) and exhaust.  Much is the same when we think of pianos – black and white keys as well as strings and hammers.  Everything in between magically gets glossed over.  But it’s in the attention to such details that make a piano go from just ho-hum to exceptional.  There are times that you sit at a piano and it REALLY responds.  That piano makes you not only sound good but it also makes you want to play MORE! That’s because someone somewhere in the world has connected the dots from keyboard to string.  More accurately, that’s the evolution of many hands spanning 200 years or more with the inception of keyboard instruments.  It’s naive to say that one person designed the car as we know it today… so too many people have been involved over the years with the development of the piano.

But there are four basic elements from which we derive “good” touch at the piano.  They all must be in check for a piano to function.  And they are:

Down weight

Up weight


Action ratio

The down weight refers to the pressure required to press down a key on a piano. The up weight is the weight needed to bring the piano key back to resting position. Friction is the perceived weight on all the joint and moving parts while the action ratio is the lever system (called whippen assembly) that multiplies the speed, weight and force of the hammer from the key.
So… in my curious nature, i start asking questions. Why do we need friction? It’s not that we NEED friction but too little of it, and parts are usually too loose and will start producing noise. Too much of it (as on the Chickering grand i just worked on) and the touch feels too heavy. Concert instruments should range between 50 and 55 grams of touch with friction representing 10-15 grams of that touch weight. With too much friction, the piano i just worked on clocked in at just over 80 grams of touch – completely unreasonable for normal playing. Question 2 – well… why not just counterbalance the touch using weights in the keys? If you’ll notice on the sides of your piano keys there are small circular weights made out of lead. Well the lead weights will have some effect for the initial movement of the hammer but in dynamic playing those lead weights will not compensate for rotational inertia at all. Nor will they do any good for either friction or up weight. So why not then just have really light parts and light friction? Good idea but… the speed of the key is also determined by the return… the return requires weight.
The balance then is this – 2 elements of the four are relatively easy to control while 2 are not. The action ratio – the intrinsic design of the piano – not so easy. That’s like saying “Can we just change the pistons on this engine?” Not easily. The second part is the up weight. The up weight carries direct correlation to the hammer weight alone. The other two factors – friction and down weight can be readily altered. Friction is by far the biggest culprit that i’ve seen. And down weight can be counterbalanced with the aforementioned weights. Once the balance is achieved however, the piano becomes a wonderful and inspiring instrument. Below are two pics of lead weighting this last week – some tools of the trade and different lead weights across the keyboard ready to be installed.

Hammer Shaping

Recently i’ve had the opportunity to work on a church piano – an older Chickering. But i must say, this piano was an interesting one to tame. I use the word tame because it was out of control. The touch was not only uneven but INCREDIBLY difficult to play. Most fine pianos have a touch weight of about 50-55ish grams of weight at the key. This one was a whopping 80+ !!! First things first… chase down the friction. That blog will be for another day though. After friction was in the ballpark, i was still faced with a piano that had a touch of 65ish grams. Time to consider putting this piano on a diet. Yep. You heard me. This piano was overweight and i was about to transform the touch.
So where does weight come from? Many months ago i wrote a blog on piano weights. It can simply (and yet so difficult at the same time) be measured in 2 forms – static weight where we are doing a dead lift – the hammer has yet to move. The other is created by rotational inertia. The hammer has started to move… how much effort is required to continue to move the mass of the hammer. The former mainly deals with soft playing… we’re not concerned about velocity but simply getting the hammer in motion. The latter however deals with everything above soft playing and truly is the more important factor. Static weight can be counterbalanced in the key like a see-saw. Rotational inertia however can really only be changed through the mass of the hammer itself. Because static weight again really only affects soft playing, when i sat and just played the piano (after friction was removed), it still felt heavy and burdensome. So it was time to trim the fat – reduce what i could on the hammer without compromising either structural integrity or tone. How does one leave the strike point of a hammer the same and yet reduce dead weight? Take a look at the pics. The one on the left is the original. Square and bulky. The one on the right – the more parabolic shaped one is one i adjusted. The tapered ‘shoulders’ of the hammer offer insignificant contribution to tone… if any. And so i spent the next 3 hours shaping hammers. Take a look at the two ‘tails’ – the end parts of the hammer. On the left – one that is tapered while the right, original. The net result? Reduction in about 1.3-1.5 grams of fat. One point three??? Perspective here… a nickel weighs 5 grams. You ask “How does anyone get excited about 1.3 grams of weight?” Ahhh therein lies the magic. Every piano has an ‘action ratio’ meaning one gram at the hammer accounts for usually around 5 grams at the keyboard. OK so do the math… this piano has a 5.5 action ration. 1.3 gram reduction x 5.5 action = 7.1 gram reduction of touch weight – the exact amount i needed to make this piano feel dynamic and alive. I’m so happy! 😀

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