Shanks parallel to strings

[Phillip Ford]

>>
>>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.

I must have missed this in my search of the archives (not an exact 
science).  I remember lots of discussions and I was aware that your 
action was set up to have the jack / knuckle contact point on the 
line at half stroke, but I didn't remember that you were advocating 
short boring the hammers.  I'll go back and try to find some of that 
stuff.


>  Many are aware of the benefits of placing the capstan/heel contact 
>on the line of centers at half blow........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....
>
>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.

I also think that we are talking about two separate issues here, 
although in an action of conventional design they are linked.

1.  Is the shank to hammer molding angle significant in and of 
itself?  The orthodox guideline is that the shank must be 90 degrees 
to the molding.  I see no reason for this and haven't heard any 
convincing arguments in its favor.

2.  Does it improve feel or performance of the action to have the 
jack/knuckle contact point above the magic line at letoff?  If so, on 
an action of conventional design, on which the geometry was laid out 
with the premise that the shank would be parallel to the string at 
letoff, then the only way to achieve this is to short bore the 
hammer.  The shank will end up being above parallel at hammer 
contact, but that's only a consequence of the setup to get the 
jack/knuckle contact to be where you want it to be.

If you were so inclined, it seems that you could design your action 
to have both jack/knuckle contact above the line and shanks parallel 
to strings at hammer contact.  As one example, you could design your 
shank so that the land where the knuckle attaches is taller and has a 
rebate for the knuckle and space where the jack ends up after letoff.

Regards,

Phil Ford