[CAUT] moving capstans question

[Keith Roberts]

Rick, it doesn't matter how you measure the action ratio, it's how you use
the results. You must remember that I set the balance weight.  The action
ratio is the measurement of the input to the output. To me if the key goes
down 6mm and the hammer rises 36mm that is a 1 to 6 action ratio. We'll call
it the Erwins Action Ratio (EAR) so we don't get into the semantic
arguements you carry on. I measured the input and I measured the output. You
can't change the EAR without changing the geometry of the action. This way I
know that my move of the action part is is not altered by the friction of
the action AND I can move it back to the original spot and it returns to the
same number. If you use weights you have to repeat and repaet to make sure
you are placing the weights in exactly the same spot and the friction is
over come the same way. So essentially with weights you take a sample of
readings and compute an average. .

So I know from using the EAR that 1 to 5.5 is a good target. Then you check.
When the capstan was placed, it was on the proper spot on the wippen heel.
The placement to the magic lines or lines of convergence was near perfect.
The reduction of blow distance to keep the same key dip gave the proper
distance above the rest rail. Aftertouch had a better feel and it was able
to carry the heavy hammers Grotrian puts on their pianos with only three
leads max in the bass. So I weighed a key and moved the leads till I had the
BW at 36 in the bass. My friction was 12. I liked it I went wih that balance
weight. There is a lot of mass in the keys on this piano so it still feels
heavy to play but it sure plays nice.

Do I care if the the action ratio was 5.52 or 5.59? No. I'm sure I could
make an arguement that shows that the BW is not exactly halfway between the
UW and the DW. Do I care? The instantaneous action ratio can change through
the movement of the action. It can have one action ratio at the start and
another at the finish as the parts move. Do we use the max ratio or the
average or a section of movement that we consider to be representative? The
reason there is a difference in these ratios is the criteria set upon the
way it is measured and not because the action puts out three different
amounts of work. The issue gets confused by suggesting that because you have
a different number for the ratio, there is something different about the
action.

What I do works in practice but I'm sure it will never work in theory.

Keith Roberts



On 9/22/07, Richard Brekne <ricb at pianostemmer.no> wrote:
>
> Hi Keith
>
> This is easy enough to contrive yourself.  It should be mentioned tho
> that the ratio measured is not the same ratio as the Stanwood ratio...
> nearly every instrument will end up yeilding two reasonbly significant
> different  results when both ratio measurements are the same.  And tho I
> have yet to check it... I dont think either of them are the same ratio
> as the Overs method.. which is more akin to what designers operate with.
>
> Important destinctions if one is thinking about using the distance ratio
> that Dales kit addresses for setting up a Stanwood like action balance.
> The resultant BW will almost always be a couple grams off.
>
> Cheers
> RicB
>
>
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