[CAUT] Keydip--how deep

[Horace Greeley]

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Hi, Ron,

At 01:46 PM 10/12/2005, you wrote:
>Hi Mike and all,
>
>There have been some good posts on this thread.
>
>>. . .  I don't think any hard-fast rule is going to suffice.
>>-Mike Jorgensen
>
>With the exception of the final jack position relative to the roller, I agree.

Yes - exactly.

>The jack position (relative to the roller) at full key dip (with the 
>hammer in check) is probably the only hard-fast rule when it comes 
>to key dip/hammer blow considerations. Since the hammer/key ratio 
>varies so widely, as others have also mentioned, even within the one 
>brand/model of instrument, there will need to be an adjustment from 
>the standard spec of dip and/or blow in many situations. Increasing 
>the blow distance on a high-ratio action will tend to place the 
>already ordinary-relationship of the jack roller contact even 
>further away from its line of centers. Reducing the blow distance in 
>the case of a low ratio action will tend to improve it.

...which problem is exacerbated in what might be called "mixed" 
actions containing parts with mis-matching geometries.

>If the dip is insufficient for a given action ratio, the lack of 
>jack/roller clearance at check may cause the action to blubber at 
>let-off, particular when played softly. If the dip is set so deep as 
>to cause considerable clearance between the jack and roller at check 
>it will slow repetition.

...especially if the performer also wants the check height set lower 
than spec (in hopes of achieving more power on repetition).

>The much mentioned problem of the hammer/key ratio varying so much 
>with the US S&S pianos got me thinking about the problem again 
>recently when retro-fitting one of my actions to another factory 
>piano (the instrument in question seemed to have a plate position 
>problem which was accommodated in the original action by fitting the 
>hammers 3 mm short of 130 mm. When I fitted my action I followed 
>suit and hung the hammers short also, since I wanted to keep my 
>action stack at the correct position with respect to the keyboard 
>(to preserve the action ratio I wanted - 5.7:1). The shorter hammer 
>position will reduce the hammer/key ratio, but only by a small amount.

Yes.

>In the factory situation, if the plate is not positioned according 
>to the standard specification, I believe it is inappropriate to 
>shift the action stack relative to the keyboard, in an attempt to 
>shift the strike position (line). If a piano is built with the plate 
>out of position, it should be a simple matter to tolerate a small 
>adjustment in the hammer position along the hammer shank. A 3 mm + 
>or - adjustment of a hammer from say a standard 130 mm standard 
>distance from the hammer center pin will allow for an 
>out-of-position plate to be accommodated without turning the action 
>geometry into a disaster.

What you have described here was the S&S factory method used until 
(at least) the late 80's, changing only slowly after the introduction 
of the Kluge keysets.  What was known as "forefinishing" was done 
largely in compensation of/for whatever errors had preceded in 
manufacture.  It does not matter if this is right or wrong.  What 
matters is that this is how things were done and explains why it is 
so important to take exceptionally careful measurements of just about 
everything in sight before beginning major action work.  Over the 
years, it was much more likely to find plates installed too high than 
too low; but this happened, as well.

>If an action stack is moved only 2 mm relative to the keyboard it 
>will have a major influence on the hammer/key ratio, which will 
>cause major headaches at regulation time (if the regulator is aiming 
>to obtain a workable regulation with standard specifications). The 
>truth is we often need to bend the specs somewhere, to get 
>real-world actions working at their optimum level.

Absolutely.

Best.

Horace



>Ron O.
>
>--
>OVERS PIANOS - SYDNEY
>    Grand Piano Manufacturers
>_______________________
>
>Web http://overspianos.com.au
>mailto:ron@overspianos.com.au
>_______________________

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