[pianotech] S&S K(52) Restoration

[Gene Nelson]

Were there were any issues with gluing up the treble part of the board first
to radiused ribs (seems to me there would be a risk of splitting the board)
then to the liner?

Gene

 

  _____  

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Delwin D Fandrich
Sent: Saturday, May 19, 2012 7:52 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] S&S K(52) Restoration

 

Ah, well, the grain angle of the soundboard panel-taken by itself-is
important in only two parts of the scale: the high treble and the low bass.
As you know a spruce panel is considerably stiffer longitudinally-to-grain
than it is perpendicularly-to-grain. We want the upper end of the tenor
bridge to see a fairly stiff load so up there it would be good for the grain
to be perpendicular to the top soundboard liner. Following this down,
however, we encounter the bass bridge where considerably more mobility is
desired and having the soundboard grain angle perpendicular to the
soundboard liner down there would further restrict the mobility of the
bridge in an area where we really want the bridge to be able to move. To
generate sound energy at very low audio frequencies you have to move a lot
of air and that means the area around the low end of the bass bridge has to
move. Since I was "floating" the low end of the soundboard panel-adequate
freedom of motion was a given-my requirements for soundboard grain angle
could be concentrated on the needs of the treble section. I extended the
treble soundboard liner up some-giving the bridge plenty of room to move-but
controlled that motion by using a somewhat unusual soundboard grain angle.

 

ddf

 

Delwin D Fandrich

Piano Design & Fabrication

6939 Foothill Court SW, Olympia, Washington 98512 USA

Phone  360.515.0119 - Cell  360.388.6525

del at fandrichpiano.com  <mailto:del at fandrichpiano.com> - ddfandrich at gmail.com

 

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Gene Nelson
Sent: Saturday, May 19, 2012 7:22 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] S&S K(52) Restoration

 

I appreciate the explaination, thank you

 

How does the steep grain angle of Terry's board fit into the stiffness/mass
transition scenario? Seems to me the treble would be especially stiff

Gene

Sent from my iPhone


On May 18, 2012, at 10:45 PM, "Delwin D Fandrich" <del at fandrichpiano.com>
wrote:

Look at the drawing below. 

<image003.jpg>

 

Ribs #2 and #4 extend across the width of the working portion of the
soundboard. The low end of the bridge has an extension that goes over the
floating portion of the soundboard liner. These three ribs provide all of
the stiffness the area around the bass bridge needs.

 

The rest of the ribs are all sized to provide the necessary stiffness to the
area around the tenor/treble bridge. 

 

In the Fandrich piano the ribs that terminate in the Z-Bar-i.e., ribs #5
through #13-are set into notches in either the Z-Bar or the soundboard
cutoff bar. The lower ribs-#1 through #4-terminate about 10 mm in from edge
of the soundboard panel. 

 

The M rim set up against the soundboard assembly do highlight the Z-Bar but
this is not quite how the Z-Bar works. The Z-Bar presents a very rigid
termination to the soundboard panel in the area around the treble end of the
bridge. The further down the scale you go the Z-Bar its termination
impedance decreases-its stiffness decreases--allowing the edge of the
working portion of the soundboard to move with increasing freedom. 

 

The termination impedance of the soundboard panel varies with the frequency
of the energy waves traveling across the soundboard assembly; the
fundamentals and lower partials are affected more by the stiffness-which is
decreasing down the scale-of the Z-Bar while the higher partials are
affected more by its mass which also decreases further away from the point
where it is solidly fixed to the back assembly. The soundboard assembly
actually appears larger to the fundamentals and lower partials; smaller to
the higher partials. In practice this has the effect of increasing the
dynamic range of the instrument through the tenor section of the piano.

 

The Z-Bar also adds both stiffness and mass to the area around the tenor end
of the bass bridge. By coupling the ends of the Z-Bar and the bass bridge
together the bass bridge extends the effectiveness of the Z-Bar further down
the scale keeping the effective area of the soundboard relatively smaller
than it would otherwise be which improves the efficiency of the soundboard
around the low end of the tenor bridge. The bass bridge is able to take
advantage of the entire soundboard area in the lower half of the soundboard
assembly.

 

That's the short version and I think I got it all straight. It's late and
it's been a very long day-I've been moving shop equipment and tools and
other stuff-so I'm not guaranteeing anything. I'm sure if I got something
turned around someone will be happy to point it out to me..

 

ddf

 

Delwin D Fandrich

Piano Design & Fabrication

6939 Foothill Court SW, Olympia, Washington 98512 USA

Phone  360.515.0119 - Cell  360.388.6525

del at fandrichpiano.com  <mailto:del at fandrichpiano.com> - ddfandrich at gmail.com

 

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org]
<mailto:%5bmailto:pianotech-bounces at ptg.org%5d>  On Behalf Of Gene Nelson
Sent: Friday, May 18, 2012 5:26 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] S&S K(52) Restoration

 

Great pics Terry, thank you.

Getting your cauls up off the floor is a nice feature.

I am having trouble seeing just how the bass bridge is supported with ribs??

Did all of the ribs get notched into the rim/Z-bar assemblies?

The M frame highlights the Z-bar frame nicely - great way to visualize the
concept.


  _____  


 

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