Action Analyses (was Capstan Relocation)

[Richard Brekne]

Bill Ballard wrote:

> It is ever so momentary. I've always assumed that the sliding
> friction between the top of the jack and the knuckle had a static
> phase, one which at the start locked the jack top to the knuckle, and
> which was not transformed into a sliding friction until the point
> where the potential energy store in the compression of the jack
> adjusting button felt finally exceeded the force of static friction
> at this spot. Remember that while the contact point on both arcs (the
> knuckle's and the jack top's) are both heading in the same direction,
> the horizontal component (sliding motion) is greater in the knuckle's
> arc, and it is also increasing. No wonder the jack is not inclined
> (no pun intended) to immediately break free of this static friction
> grip with the knuckle.

Yup... real easy to see actually when you look for it. And easier if you pull down
the repetition lever and move the key very slowly (I used an action model to do
this). As for the spreads affect on this, the same ease of observation is true. If
you have the jack top such that the top surface tilts ever so slighty downwards
(front end of jack surface) from the knuckle, then you have the back edge of the
jack in contact with the knuckle at key rest. Both arcs are moveing in the
direction of the back of the action (with the exception of the begining phase of
the jacks when the whippen lower then horizontal, a condition that also can
influence this jack kind of movement me thinks..) Anyways.. when spread is set up
such, as the jack rises its surface starts "tilting" backwards and the total
surface area meets the knuckle as the knuckle rises up and away. It cant "tilt"
backwards the other direction much if at all before the jack tender ends the
process.  You get sortof  a "  )(  " out of it all.

This also seems to correspond to top action spread setting that gives the least
amount of drop relative to letoff when the letoff button and jack tender hit there
respective levers at the exact same time.. curiously..

>
>
> I'm not sure that this is the explanation for the effect, or whether
> your observation regarding the spread contains the answer. It would
> seem quite likely that this effect could still occur even in an
> action in which axes and contact points had been properly dealt with,
> such as in Ron's action.
>
> How modest of Ron not to respond when I asked if he had anything to
> tell us about his action. Seriously! He'd given a full description of
> it in a thread I'd missed last month.

>
>
> Bill Ballard RPT
> NH Chapter PTG
>
> "No one builds the *perfect* piano, you can only remove the obstacles
> to that perfection during the building."
>      ...........LaRoy Edwards, Yamaha International Corp

--
Richard Brekne
RPT, N.P.T.F.
Bergen, Norway