Touchweight Metrology Question

[Farrell]

Richard wrote:

"Basically what I do is to pick a SW curve based on the target ratio I want,  install FW to fit the FW max table ...."

How do you relate/figure SW to SWR? I thought target SW should be based on piano tone, and then geometry and FW and whatever adjusted to accomodate the desired SW?

Unfortunately, this piano appears to have new Yamaha hammers on it. But they are not tapered, or arced. Friction in the hammer-shank flanges is all over the place. Is it reasonable to try the water/alchohol thing to shrink-size the bushings before repinning the whole shebang? I wish the hammers and knuckles were more worn, then it would be easy to recommend a new top half of the action.

By installing FW to "fit" the FW max table, are you suggesting that FW should be at or near that maximum value? If so, why? Doesn't "maximum" in this case mean that "at that value or below is fine"? Or not? Thanks.

Terry Farrell
  
----- Original Message ----- 
From: "Richard Brekne" <richard.brekne@grieg.uib.no>
To: <pianotech@ptg.org>
Sent: Wednesday, May 15, 2002 3:11 AM
Subject: Re: Touchweight Metrology Question


> Farrell wrote:
> 
> > I am taking my second stab at touchweight metrology analyses of an action (my first was half-hearted and incomplete). Yamaha G5, 1963, action in very good condition. Complaint: action heavy. It is indeed with DWs all over the 60 to 80 gram range (mostly around 65 grams). Some notes do have a lot of friction, but many measured notes only have 10, 11, 12 grams friction, so clearly there is a problem with either too much weight hanging out somewhere, or bad geometry. KR is 0.49, BWs are mostly around 50 to 55 grams or so. I have not measured strike weights and wippen radius weights yet.
> 
> KR of 0.49 is down there quite a bit... which means the capstan is in a good ways and you should be able to lift all kinds of weight, but need lots of key dip to get things to work.  So if you are in addition experiencing medium heavy to heavy DW then you probably have a fun job on your hands.
> 
> But this is real sketchy just with KR and vague DW, BW and Friction hints.
> 
> I like to take a few (10-12) samples of all parameters to get an idea of where the action is, then plan what I want to end up with a "least work possible" perspective. I aggree with David that ending up around 5.75 SWR is a good generic solution that seems to work well with most actions.
> 
> Basically what I do is to pick a SW curve based on the target ratio I want,  install FW to fit the FW max table David includes with his kit, and adjust leverage as neccessary to make a decent enough fit.
> 
> Make sure the action spread and friction issues are taken care of ahead of time.
> 
> > Maybe too early yet to even be asking questions. Just wondering if anyone that is familiar with this process has any recommendations. Thanks.
> 
> This proceedure makes for a decent generic solution, and gets you started along the Stannwood path. It gets you looking at and using his formula in a few different ways, and you start routines in his practical methods. It doesnt allow for much "design" work tho as you are pretty much stuck with a very narrow set of SW and FW parameters. But its a good and easy place to start.
> 
> In your case, if your KR is indeed only 0.49,  I would guess you might end up moving the capstan line back a bit
> 
> > Terry Farrell
> >
> 
> Grin.. Ed will correct me if I am thinking backwards again. It gets worse when I think upside down :)
> 
> 
> --
> Richard Brekne
> RPT, N.P.T.F.
> Bergen, Norway
> mailto:rbrekne@broadpark.no
> http://home.broadpark.no/~rbrekne/ricmain.html
> 
>