[CAUT] moving capstans question

[Richard Brekne]

Hi Keith... just a couple of comments to a post I found most agreeable.


    Rick, it doesn't matter how you measure the action ratio, it's how
    you use the results.

I agree with this as far as it goes... Indeed, I've been doing something 
along similar lines for a long time and compensating for any error in my 
target BW later on in the process.  My point was that if you are first 
going to do things Stanwoods way, and expect to end up at your target 
BW.. then you have to rely on his Strike Weight Ratio.  If you use some 
other ratio.. and then follow Stanwoods methods... you will have to 
compensate somewhere along the line to get your BW right.  Most of the 
time anyways.

    You must remember that I set the balance weight.  The actionratio is
    the measurement of the input to the output. To me if the key
    goesdown 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 Iknow 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. .

It works that way sure enough.  But the 6:1 EAR probably will not be a 
6:1 SWR.  In my experience (and I have about 40 different action samples 
where I have checked this) the SWR ends up slightly lower.  Last I heard 
David was working out some way of transposing from one to the other... 
but I dont know if he has gotten there yet.  Point being is that input 
of  6 mm key movement yielding 36 mm hammer movement will almost never 
corresponding relationship of weight.  Not that this is all that big a 
deal,  as long as one keeps ones P's and Q's in their correct 
perspectives all is well.


    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.

Fair enough... and pretty much what I do as well.... except I take the 
ratio differently... but as you say...


    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.

It DOES matter however if your ratio error ends up being more like 5.52 
or 5.82... which can happen.  Then you have to compensate later on in 
your process by either adding an appropriate amount of lead to the 
keys.. or taking away from the hammers.


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

I'm sure it does... you know what you are doing and will get an 
excellent result each and every time I'd bet. Actually your point is the 
same as the main thrust of the article I wrote dissecting the Standwood 
formula a couple years back... there are several ways to skin a cat 
really... as long as you know what skinning is all about :)


    Keith Roberts

Cheers
RicB



    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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