Regulating Lost Motion


Regulation is the act of adjusting a piano’s action so that each key responds well, can play softly, and doesn’t hit twice or block on the strings. There’s a bit more to it than that, but that’s a good basic definition.

Regulating a piano can be a complicated affair. Adjustments you make to one part, can affect the measurements of another. I have developed a concept that simplifies action regulation so that anyone can understand these relationships and know what adjustments to make to improve the feel of a piano, and if there is room to improve it at all. It is called “The Regulation Triangle”. At the time of writing of this post, I had not posted any description of it.

Before these analyses can be done, some basic adjustments must be made in order to have the action work its best, and have the regulation adjustments you make, not change as you work.

One of these basic adjustments is Lost Motion.

Basically there are three parts to a piano key action. The key, the wippen, and the hammer.

The key is the long piece of wood you press on, and pivots. As it pivots, the back end pushes up on the wippen, which is a moving part that transmits motion from the key, to the hammer.

The hammer rests on the hammer rest rail, unless the wippen is too high, then the hammer rests on a piece in the wippen, called the jack.

The jack is where the motion from the key is passed on to hammer; the jack presses up on the bottom of the hammer.

The jack slips out of the way when the key is pressed almost all the way down. This produces a “throwing” type of action the allows the hammer to be “thrown” at the string. It is a very natural feel.

In order to replay the note, the jack must “reset” under the hammer when the key is returned to its resting postion. (On grands, the jack resets must sooner. Grands do not have lost motion.)

Proper working of the key/wippen/hammer involves the key moving, the wippen rising slightly until the jack touches the hammer, and then the whole system moving together (until let off, but that’s another story).

There is a capstan at the back of the key that rises up to meet the wippen. It can be adjusted up or down, which moves the wippen, and hence the jack up or down.

If the capstan is too low, the key will move too much before the jack engages with the hammer. This is called “Lost Motion”; the beginning motion of the key does nothing.

Now, if the capstan is too high (the jack is too high), the hammer will be resting on the jack, instead of the hammer rest rail. After one playing, the hammer may fall down to the rest rail once the jack is out of the way (after let off) and leave no room for the jack to reset. When this happens, the key stops working. You can press it down, but the hammer doesn’t move, because the jack isn’t under it. This is sometimes called “Negative Lost Motion”.

Here is a simple way to adjust Lost Motion.

Gently pull back on the hammer rest rail. All the hammers should move with the rail, because they should all be resting on the rail, not the jack. If they are resting on the jack, they will not move with the rail; you will not see them follow the rail. For any that do not follow the rail, give the capstans a quarter turn down and retest with the gentle pull.

Once they are all moving with the rail during the gentle pull, pull a little harder. Now, they should all stop moving. This means there is a tiny clearance between the tops of the jacks, and the hammer. If the clearance is too much, the hammers will keep following the rail as you pull it back. If Lost Motion is excessive, the hammers will never stop following the rail.

Turn the capstans up a quarter turn for each hammer that won’t stop moving and keep following the rest rail on hard pulls.

With this simple procedure, you will be able to improve lost motion so that no keys stop working, and there isn’t any excessive lost motion between the key and the hammer that will affect the feel and the tone.

On some pianos, there may be a dimple up under the hammer, caused by the jack wearing away the leather under the hammer. This will result in clearance when the key is at rest, but not enough clearance to allow the jack to reset.

The only way to be sure that the jack has enough room to reset, is to trip it by using a screwdriver or something to push down gently on the jack toe. This will trip the jack. When you let go, it should return easily under the hammer.

Adjusting lost motion can be an easy way to improve a piano’s action and feel/response, and it is one of the easiest regulation procedures to perform; anyone can do it.

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