back action replacement questions

[Overs Pianos]

Gene  and all,

>Gene----consider changing the pivot point of the back action to comply with
>the "pivot points" of the keyframe and stack.  The protocols are fairly
>simple; call Dale Erwin or Stephen Bellieu; they've both done it for me a
>number of times.
>
>David A.

This point of David's is most important. Avoid replicating the 
mistakes of the manufacturer. For a great number of pianos, including 
many made by a certain maker who lays claim to the high ground, the 
location of the pivot point for the back action is way off optimum. 
We've all seen damper lift pads with large depressions worn into the 
felt from not-so-many years of contact with the damper lever.

The pivot point for the damper lever tray should be set such that, 
when the damper lever is at half lift height, the contact between the 
damper lever and the key is on the line of centers between the pivot 
point and the key balance pin hole center.

You can check visually to see if the pivot is set at the correct 
height. At the base end of the piano, shine a light into the action 
back so that you can see the damper lever and key. Depress the key 
and watch the relationship between the damper lever and key as the 
key is depressed. If there is visible horizontal movement between the 
key and damper at their contact point, then the pivot height is 
wrong. Typically, the pivot is set too high.

An incorrect pivot height results in unnecessary friction between the 
key and damper lever. An understanding of this concept is not new. 
We've been adjusting the pivot height in rebuilt instruments for many 
years. When I was at Reno in 2001 I saw that Rick Baldassin covered 
this issue in his class.

Its also worth noting that an alteration of the pivot height will 
make very little difference to the length of the damper wire 
required. The height of the damper lever end will remain the same, 
since the back of the key height remains unchanged. Therefore, unless 
the damper wires were cut so short that the grub screw is clamping 
right at the end of the wire, it will be possible to change the pivot 
height without changing the damper wires. Sometimes you'll need to 
make a new damper up-stop rail, since the slot adjustment may not be 
adequate if you have to lower the pivot point.

I hope this makes sense.

Ron O.

-- 
OVERS PIANOS - SYDNEY
    Grand Piano Manufacturers
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Web http://overspianos.com.au
mailto:ron at overspianos.com.au
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