Key Ratio ?

[Richard Brekne]

John Hartman wrote:

> Richard Brekne wrote:
>
> > So... I ask you...  why we are supposed to measure down to the balance
> > rail, and up to the capstan and at the same time  not take into
> > consideration the horizontal deflection of their angles before figuring
> > their ratio ?
>
> There are a number of different ways to measure key ratio. Which one you
> pick depends on the what you are trying to find out. For static weight
> measurements measuring along the key perpendicular to the force of
> gravity is best.

That seems clear enough, and I find it curious that the quantity of Balance
Weight so well conforms to measureing all three levers very much  in this
fashion. In fact, when you think of it,  that the Stanwood measurements yeild
the correct quantify for BW so well is kind of odd given the fact that the
weight measuments taken have all the parts in an orientation they never all
three find themselves in at the same time in the action itself.


> If you are working on how the action moves angularly
> you need to measure the key differently.

Dont you also have to take into consideration the orientation of the parts at
the their starting point. In the example I gave, it seems clear that the
amount of purely vertical movement in the back of the <<key>> compared to the
front is going to vary dependent on where in their respective arcs each point
is at the start of motion. If the <<key was tilted forward enough... grin...
the back end would actually pass through the top of its arc,... or if it was
tilted back from horizontal it could rise more with downward motion at the
front. In that sense it almost seems meaningless to talk about a ratio which
mixes change in vertical movement with a lever that moves in an angular
fashion. Yet this is exactly what we do all the time.


> To get true measurements of the
> lever lengths of action parts you need to have the action assembled.
> There are only two measurements that can be gotten directly from the
> parts - the front length of the key and the back length of the shank.

What do you mean by the back length of the shank ?

>
> All the other lever arms  are out somewhere in space and change
> throughout the key stroke.

Hmmm.. something about this gives me that itch on my left temple.... :)

>
> The link below from my web site is a drawing of the pitch point of the
> upper half of the action. The action is at half stroke. If you draw
> these out for other positions of the stroke you will see that the ratios
> change.

What do you mean by the "pitch point" ?

[link redacted at request of site owner - Jul 25, 2015]
>
> John Hartman RPT

Thanks for the reply John.

--
Richard Brekne
RPT, N.P.T.F.
UiB, Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html
http://www.hf.uib.no/grieg/personer/cv_RB.html