[CAUT] Keydip--how deep

[Overs Pianos]

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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.

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.

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.

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.

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.

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.

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