[CAUT] Digest, Vol 1103, Issue 85 Moving Wippen Rail

[Richard Brekne]

Hi Keith

I'm not about to argue the point of the change in leverage. Thats been 
hashed through already and you've made some very good points for 
ponderment.  But I deem you have it wrong about the friction.  Friction 
between the jack and knuckle has to do with the interface between jack 
and knuckle top.  It makes no difference to this interface that the jack 
is being supported by the jack center... the interface still sees its 
own condition. My own measurements confirm that friction increases when 
the jack is significantly out of line. Geometry theory suggests the 
same.  Virtually every action designer will make a very large point of 
this, and every manufacturer specifies this.  And... as I said last time 
we have several articles written in the PTG on the matter.

Jon Page set me on a course several years ago in a discussion about 
capstan placement and whether this should be done from just a strictly 
weight / leverage perspective or whether it should be done from an 
action geometric perspective.  Ever since then I set up actions so that 
their geometry is as optimal as I can get it... and then I deal with 
leverage / weight issues by simply balancing appropriately whatever 
Strike Weights I choose...which in turn are limited by the maximum key 
leading I allow for.

If I DID want to change action leverages. (And I do some time) Then I 
treat that task as a holistic one. And I go about it from an action 
geometry perspective. Like regulation... this is all very 
inter-reactive.  Changing one parameter has consequences for at least 
more then a couple others.  My goal is to get as fine a geometric 
condition as I can get for whatever leverage I am after, and THEN 
balance the hammers and keys.  Seems to yield the best results and a 
growing understanding of the complexities of the action... which seem to 
be really a never ending adventure when it comes down to it :)

Thats my story... and I'll stick with it until one of you guys .... 
grin.. moves me on the issue.  And believe me,  whether it sounds like 
it or not,  I AM always open to change.

Cheers
RicB


        On 10/30/07, Richard Brekne <ricb at pianostemmer.no> wrote:
         >
         >
         > In anycase, moving the whippen rail is a matter of creating this
         > alignment and not a matter of changing touch weight.



    Sorry Rick but that doesn't agree with the data. The action I was just
    working on Dale weighed off yesterday and he had been trying to
    squeak an
    extra lead out of the keys. It was weighing off with 4 leads in the bass
    when regulated. After the rail move it weighed off with 3 leads. This is
    because the resistance arm when measured to the top of the jack is not a
    direct ratio to the effort arm. The force has to be translated
    through the
    jack first. Remember weigh-off is only to let off so miss alignment
    of the
    core to the knuckle core will make no difference as long as the jack is
    pointed at the center of the knuckle.

    So to figure the force directed out the jack, you make the line from
    wippen
    center pin to the jack center pin the x axis and then the tangent
    line is
    the y axis. By the number of degrees you calculate the amount
    directed back
    down the x axis and then you figure the resultant force vector directed
    down the jack. Then resolve the force at the end of the jack to the
    tangent
    line of the arc from the top of the jack to the wippen center pin. There
    will be a slight movement of the magic line but when 2 mm is
    translated in
    degrees back to knuckle it is nothing.

    In any event like David Love said and what my mentor thinks agrees
    with the
    data: there is a change in the amount of weight needed to balance an
    action
    and there is no measureable change in friction. Personally I don't
    see how
    you can change the effort arm of the wippen and not effect a change in
    leverage.

    That's my story and I'm sticking to it.

    Keith Roberts