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

[Keith Roberts]

Excuse me, you are not accepting the fact that the resistance lever arm is
to the jack center pin. This by definition of a lever. Show me the solid
beam that translates the force from the capstan directly to the top of the
jack. You have an imaginary RA. The force is transmitted through the lever
arms to the jack center pin. The center pin then lifts the jack. If I change
the EA of the wippen, the force at the jack center pin will change. Am I not
correct on this? The premise you base everything on is that the RA changes
with the rail move. It does not so a 2mm move is a lot and the input at
center pin to the jack, even though it changes slightly with the rotation of
the jack, is counter acted by the change in the alignment at the top of the
jack. Therefore all of the resultant changes MUST be due to the change in
the EA of the wippen.

Picture this. A five story building. You have a motor that  lifts a whole
bunch of weight 3" and lets it back down. You need work done on all the
floors. You put the motor in the basement and stand a post up through the 5
stories. On the 5th story you have machine that is the most important and
needs to accelerate a part from the floor to the ceiling and you need more
lift of the post to make it work. So you put in a 2nd class lever in the
basement between the motor and the post. Now this post does this same work
on every floor. Do I measure the RA of the lever in the basement to 5th
floor, the 4th floor, the 1st floor? If I disconnect the equipment on the
5th floor and move it to the 2nd, do I have to recalculate the RA and adjust
the setup so the same work is then accomplished?

Keith Roberts

On 11/1/07, Richard Brekne <ricb at pianostemmer.no> wrote:

> Hi Keith
>
> Ok... lets look away from where the lever is measured for the moment and
> just agree however we take it, it remains a third class lever.  And lets
> take a simple example lever and ratios for key and hammershank and do a
> quick calc on what happens with a 2 mm move that lengthens both arms of
> the whippen.
>
> Say the input arm is 100 mm and the output is 150. Say also that the
> hammershank has a 7.0 ratio and the key ratio is 0.5 figured at 100 mm /
> 200 mm
>
> The sum ratio before the 2 mm move is then 7.*0.5*150/100 = 5.25
> The sum ratio after the move is then 7*0.5*152/102=5.215
>
> Altso... a net change of 0.035 in total ratio.  Not much there to go on.
>
> Remembering  that taking down and up weight measurements is at best an
> iffy thing.... hardly in the ballpark of an exact science,  I am forced
> to wonder about all this.  True enough the changes in the arms dont
> exactly cancel each other out entirely, but you have to move the whippen
> rail quite a bit to force a significant change. So much so that the jack
> angle will be way out of kilter with its geometric requirements. I cant
> see any way you can really change the ratio much with a 2 mm move unless
> you either figure in (and explain) some other component, such as jack
> angle / force vectors (in which case our third class lever suddenly
> becomes a good deal more complex).
>
> Thoughts ?
>
> Cheers
> RicB
>
>
>    Any gain in touchweight is a product of a reduction of friction or a
>    gain in
>    leverage, Both of which can happen when aligning to the lines of
>    convergence. (Did I miss any other things?) Friction is measurable
>    and has
>    been eliminated so that leaves one thing.
>
>    I repeat, the load arm of the wippen is to the jack center pin. The
>    jack is
>    only a transitory post and is not a lever. Please define what the word
>    "jack" means in this case if it is not what I say.
>
>    Keith Roberts
>
>
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