Touchweight Metrology Question

[David Love]

Terry:

Well they didn't exactly get the balance rail right did they?  The sharps
have a different KR than the naturals and thus the SWR varies considerably.
You will have to decide where to compromise or to have a varied capstan line
to get even SWR.  A move of the capstan of 2-3 mm toward the balance rail on
the sharps will drop the SWR by about the right amount if you want to go
that route ( you should check this by experimentation).

It appears that you generally have quite a bit of room to add lead.  For
example:  Remember that 1 g added to the FW reduces the BW by 1 g.  So on
note 28, with a BW of 48.5 adding 10 g to the FW would still leave you under
the FWC.   On note 52 adding 18 g to the FW would still leave you below your
FWT.

If the hammers are untapered, then you could easily remove 1 g +  from the
SW by simple tapering and tailing.  I don't think that would have a negative
effect on tone.

The biggest problem is what to do with the different SWR between sharps and
naturals.  Given the limited budget, I would probably use the naturals as a
guide and let the sharps fall where they fall.  For example, on note 53, if
you reduce the SW by .5 g, you will reduce the BW to approx 54g.  To achieve
a 38 g BW you would need to ad 16 g to the FW which would put you at 24,
just below your FWC.  Assuming that is a representative sample, that
naturals around there would be well under the FWC.  Moving the capstan line
on the sharps is not that big a deal.  Thirty-two capstans wouldn't take
that long assuming there is room under the heal to accommodate the move
without refelting.

If you are not going to move the capstans, I would follow this procedure.
Calculate the SW curve based on a BW of 38 - 40 g (your choice), an R of 6.0
and use the FWC in the equation.  That will give you the maximum SW for the
sharps to keep the FW at maximum.  Then take some samples SWs and see if
that is achievable in terms of tapering and tailing without having to remove
too much weight from the hammers.  If that requires too much reduction in
the SW, then either allow the FW to go over max for the sharps, or push up
the BW until you get the compromise you want.  Take off each hammer and
shape to get the SW curve, check the pinning and replace.  Then use the BW
method of setting the leads in the keys.  I think that will give you a good
result.

If your average SWR is 5.5 on the naturals, you should not have a problem
with regulation.

David Love

----- Original Message -----
From: "Farrell" <mfarrel2@tampabay.rr.com>
To: <pianotech@ptg.org>
Sent: May 16, 2002 5:43 PM
Subject: Touchweight Metrology Question


> Well, I'm trying to plug along here with my Yamaha G5 heavy action. Below
is a table of my data for ten sample notes (I hope it comes through
un-screwed up). I think all is fairly self explanatory perhaps except for
the last four columns. FWC is Front Weight Ceilings (from Stanwood data
tables). FWT is Front Weight Targets, which is the FWC, less 10% (safety
factor). BWC is Balance Weight achievable with using the ceiling FWs. BWT is
Balance Weight achievable with using the target FWs.
>
> #    DW  UW   F      BW     FW     KR    WW    KC     SW    R    FWT  FWC
BWT BWC
> 16   61   37  12.0   49.0   29.0   0.49   18.4   16.5   11.9   5.8   33.8
37.5   44   41
> 17   67   39  14.0   53.0   30.3   0.49   19.4   16.5   11.9   6.2   33.5
37.2   50   46
> 28   59   38  10.5   48.5   23.1   0.48   18.9   16.5   11.3   5.5   30.6
34.0   41   38
> 29   73   48  12.5   60.5   17.7   0.50   19.1   16.5   11.2   6.1   30.3
33.7   48   45
> 40   67   40  13.5   53.5   14.1   0.48   19.7   16.5   10.5   5.5   27.0
30.0   41   38
> 41   72   46  13.0   59.0   13.5   0.50   18.5   16.5   10.4   6.1   26.6
29.6   46   43
> 52   66   47    9.5   56.5     3.6    0.48   18.6   16.5     9.6   5.3
22.6   25.1   38   35
> 53   68   46  11.0   57.0     8.0    0.50   18.4   16.5     9.5   5.9
22.2   24.7   43   40
> 64   62   41  10.5   51.5     2.6    0.48   19.3   16.5     8.3   5.4
17.2   19.1   37   35
> 65   63   41  11.0   52.0     6.7    0.50   19.0   16.5     8.3   5.9
16.7   18.6   42   40
> 76   59   41    9.0   50.0    -1.7    0.48   18.3   16.5     7.3   5.4
10.4   11.6   38   37
> 77   62   42  10.0   52.0    -0.3    0.50   18.8   16.5     7.1   6.0
9.9   11.0   42   41
>
> Action spread is right on the money at 112.5 mm.
>
> My SWs are right along the divide between medium and heavy hammers on the
smart chart. I should think this is a reasonable weight set of hammers. I
see someone forgot to put lead in the keys along the line somewhere! But I
also see that even if I go right up to the FW ceiling, I will be a bit over
ideal DWs.
>
> Not having seen all this data before, it seems rather erratic to me. How
in the world can the BWs range from 49.0 to 60.5? And that is with a very
smooth SW. I assume this is mostly erratic leading? Leading is two in bass,
one in tenor, small one near center rail in treble, and one in rear of key
in high treble. I just played around a little with weighting key #16, and I
would have to add two big leads and one small one to get near the FW Target
or Ceiling. But perhaps that is OK - basically three big leads in the bass
keys.
>
> Recommendations?
>
> I should point out here that this piano is in a small church, and it seems
that the piano is not a high priority for spending money - so I'm probably
not going to get to do everything I might want.
>
> I could trim all hammers, but I hate to have hammers too light for tonal
reasons. Geez, I look at this mess and start to think that I simply need to
take a saw and cut off everything above the keyframe and start all over.
Help!
>
> I know I can trim hammers a bit, and add lead until I get about to where I
want to go, but that seems so........ pre-cambrian. Waddaya think?
>
> I think I also need to regulate out a few notes to be sure that the
current geometry is not requiring excessive dip.
>