Frank Benner
piano techncian

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technical subjects

How do the action parts move?

The action of a piano or grand piano has a great number of moving parts. When we press a key, it puts into action: a whippen, a hammer and a damper! All these moving parts have their own hinge points.

One part of the hinge point, the so-called flange, is screwed on its rail.
The other part must be able to move.
The hinge point, the center pin, is locked into the wood of one part and is able to turn in the other part.
The little hole in that part is lined with cloth to make this possible. This is called the bushing.

This is a blown up picture of a part of the flange.
Very clearly one can see the bushing with red cloth and the center pin.
The hole in the wood is only 2.5 mm Ø, the center pin 1.3 mmØ

This technique has the advantage of a very small scale and a great durability.
The disadvantages are: wear and tear causing unwanted slacking of the parts. The bushing can become to loose causing the action part to tick.


In this picture you can see the action of a grand piano with its hinge points.

High humidity is a greater enemy: damp, but also the use of lubricants, causes the center pins to get stuck in the long run, with a slow reaction of the action as a result.
It will get more and more heavy to play the piano and in the end it will be impossible, when different parts get completely stuck.

A piano should always be in the right climate and the hinge points should never be lubricated. Lubrication causes the hinge points to get rigid.
When the action parts tick or get rigid they need to be repinned. The action must be disassembled and the old pins are one by one pushed out of the wood.
The bushing cloth needs to be reamed with a special reamer and after that a new, one size thicker pin, will be pushed into the flange.
Repinning is a very meticulous job because the new pin is only 0,025 mm thicker than the old one.
If the bushing has become greasy, through the use of lubricants, it has to be replaced: a very time-consuming, expensive job.

To give you an idea of the size of the of the hinge points: a match is put beside it!

One needs to take away exactly the right amount of bushing cloth with the reamer.
It takes a lot of time because a modern piano contains over 330 pins and a grand piano even 490 or more!