Shanks parallel to strings

[Overs Pianos]

>At 11:17 AM -0700 18/6/04, Phillip Ford wrote:
>
>
>One thing that nobody raised in this discussion was anything about the
>jack / knuckle contact point and its relation to the 'magic line'. 
>Most action
>manufacturers seem to set up their actions so that the contact point is on the
>line between wippen center and hammer center at letoff.  We may say 
>that letoff occurs
>at a certain point.  However, the process of letoff is really 
>happening over some
>portion of the key stroke, from the time the jack tender first 
>contacts the letoff
>button until the jack escapes.  During this time the jack is 
>rotating about its own
>center and the contact point is moving slightly.  I wonder if, with 
>a conventional
>action arrangement, having the shank go slightly beyond parallel is 
>doing something
>beneficial to help the jack escape more easily or transfer a little 
>more power to
>the hammer.  Any thoughts about that?
>
>Phil Ford

I've been reading the posts Phil but haven't felt any contribution 
compulsion until now.

I've written about this more than once on the list. On the several 
occasions that we've discussed action geometry (there was a 
particularly active flurry of discussion immediately following the 
Reno convention in 2001). I've suggested that the improvement in the 
jack/roller contact relationship is one of the main benefits in 
setting the bore distance so the hammer shanks are over-horizontal 
when the hammer strikes the string. Many are aware of the benefits of 
placing the capstan/heel contact on the line of centers at half blow, 
while ignoring the fact that for most conventional modern actions, 
the jack/roller contact is around 7-8 mm below the line of centres at 
rest, reducing only to 1-2 mm below the line of centres at let-off. 
If someone were to set up a capstan/heel to contact this poorly, 
they'd be howled down by the myriad of techs who know better. But 
when it comes to the contact between jack and roller, that particular 
aspect of the action seems to be immune for the normal laws of good 
design.

Indeed, some on this list and elsewhere have defended the poor 
relationship between the jack/roller contact, claiming that it is 
important for the 'feel' of the modern action. After building five 
grand pianos with our new action, I am now convinced that such claims 
are 'bollocks'. For those on the list who are not familiar with the 
design of our action, one of its many design improvements was to 
position the jack/roller relationship so that it is on the line of 
centres at half blow, ie. 3.5 mm below the line of centers at rest, 
and 3.5 above at let-off. A line drawing of the action can be found 
at;

http://overspianos.com.au/actn.html

So getting back to your post Phil, yes I do believe that setting a 
conventional action to over-center will and does help the efficiency 
of the action. When standard actions are set up so that the hammer 
shank is basically horizontal at strike point, they tend to have a 
pretty ordinary 'touch'.

One high end concert piano I look after in Sydney has a generic 
boring of the hammers (ie. they are not bored for the individual 
piano), and a keybed to string distance in the bass which is a little 
shorter than usual. This action, which has no obvious friction issues 
or other vices, does not play very well. The shanks in the bass are 
under centre at the strike point. We've changed similar actions from 
on or under centre to over-centre in the past and noticed a 
significant improvement in the touch. However, such modifications 
need to be approached with caution. Some pianos have such deep pin 
blocks that there is a risk that over-centering the action can result 
in contact between the shanks and the pin block.

Ron O.
-- 
OVERS PIANOS - SYDNEY
    Grand Piano Manufacturers
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