Touchweight Metrology Question

[David Love]

Take all measurements for several sample keys throughout the keyboard in
order to compute the average SWR in the system.

by Stanwood's formula:  (R = SWR)

R = ((BW + FW) - (KR x WW))/SW

Rewrite the equation with SW as the variable:

SW = ((BW + FW) - (KR x WW))/R

Select a note that you sampled with a measured SW, say note 40.  Into the
equation above, input the maximum FW according to Stanwood charts for that
note, the desired BW, and solve for the maximum SW (KR, WW and R are
givens).  If your measured SW is above the maximum at that BW, then push up
the BW until you get to your measured SW.  If that BW is higher than you
want, you will have to change the geometry or reduce the SW (or add an
assist spring).  If the measured SW is lower than the calculated maximum,
then you should be able to add lead to reduce the BW without exceeding the
maximum FW.   Do this for several samples.

If you want to know directly the BW that can be achieved without exceeding
FW maximums, rewrite the equation as:

BW = (KR x WW) + (R x SW) - FW

And use as inputs the measured KR, WW, R, SW  plus the maximum FW according
to Stanwood charts.  That will give you the lowest BW that can be achieved
on that note without exceeding FW maximums.

Make sure you address friction before taking measurements.  They will be
much more accurate.  SWR should be below 6.00.  I find the ideal to be
around 5.75 in terms of regulation.   SWR's will vary because of
manufacturing errors, i.e., knuckle placement, capstan alignment, etc.. So
when redoing the whole system it is best to use an average and err below the
FW max by reducing it by some percentage.

You see, there was some reason for those algebra classes in high school.

David Love


----- Original Message -----
From: "Farrell" <mfarrel2@tampabay.rr.com>
To: <pianotech@ptg.org>
Sent: May 14, 2002 7:39 PM
Subject: Touchweight Metrology Question


> 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.
>
> I have yet to go through and complete the Stanwood data sheet (I'm about
half way through). My question at this time is general in nature: Is there
any specific area I should be targeting for analyses? I guess I just feel
like I'm collecting this data and don't have a clue as to what I'm going to
do with it. I'll re-read David's Journal articles also.
>
> Maybe too early yet to even be asking questions. Just wondering if anyone
that is familiar with this process has any recommendations. Thanks.
>
> Terry Farrell
>
>