Killer Octave Question

[Farrell]

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Ron O. wrote:

"Look up your engineering handbook."

I don't own one. Never opened one. I was a geologist in a former life - =
never an engineer. Do you or anyone else have a recommendation for a =
good basic nut & bolts Dr. Suess-level engineering reference book. I =
guess if I'm going to build a rib I need to start understanding what =
effect various dimensions, etc. will have on its performance.
 =20
"The paring (you might have a different term for it) at the ends of the =
ribs...."

Oh, you mean the taper of the rib from the maximum height in the middle =
section to a lesser height near the ends. OK, gotcha.

"By the way Terry, congratulations...."

Thank you very much for the comment on APPARENT good progress. Perhaps =
best to save the congrats (if deserved) for after we play the =
instrument! I do have very high expectations though. I gotta admit that =
when I laid the ribs into their new notches and stood back for a moment, =
I just about jumped out of my shorts. WOW! Happy boy..... for now.

----- Original Message -----=20
From: "Ron Overs" <sec@overspianos.com.au>
To: "Pianotech" <pianotech@ptg.org>
Sent: Sunday, April 13, 2003 10:12 AM
Subject: Re: Killer Octave Question


>----- Original Message -----
>From: "Ron Overs" =
<<mailto:sec@overspianos.com.au>sec@overspianos.com.au>
>Subject: Re: Killer Octave Question
>
>SNIP
>
>  > Sure the long bridge will rotate backwards
>>  on its axis (from end to end) just slightly to accommodate the crown
>>  of the board, but it will be so minimal as to be insignificant.
>
>Please try and clarify the above statement. Are you defining an axis=20
>going from the extreme treble end to the low tenor end of the long=20
>bridge? Then are you speaking of the two ends rotating backwards to=20
>meet the crowned board? I guess then one could speak of the killer=20
>octave area (or thereabouts) rotating forward if the the two ends=20
>are considered as reference points?

If you imagine a line which passes through each end of the long=20
bridge, the bridge rotates around the axis of that line such that it=20
rises in the middle to accommodate the rising centre of the sound=20
board. When we started installing entire long bridges, we had it in=20
mind that we would crown the underside of the bridge to fit the crown=20
of the board, similar to John's suggestion. But when we built the=20
first basic bridge blank, we noticed that it fitted the board's=20
crowned profile almost perfectly as is. Consequently, we haven't=20
bothered crowning the underside of the bridge to this day.

>
>  > The
>>  rib profile,  'stress in extreme fibre' and paring profile is where
>>  its at!
>
>I'm trying to understand this statement. Rib profile - OK, the=20
>shape/curve of the rib.

Yup.

>Stress in extreme fibre - what is that?

Look up your engineering handbook. The chapter on beams as load=20
bearing structures has the info. The maximum stress in extreme fibre=20
is the loading within the beam which results from a given load (this=20
is always at a maximum at the top and bottom of the beam, and=20
virtually zero in the middle). After reading about the behaviour of=20
beams, take a look at any 1900 Bl=FCthner or Bechstein board with their=20
low 18 mm high sound board ribs. No surprises as to why they've sunk=20
out in the middle right under the long bridge. Its all about=20
excessive 'stress in extreme' fibre.

>Paring profile - totally lost on this one - what is that?

The paring (you might have a different term for it) at the ends of=20
the ribs have a marked influence over the tonal outcome. Have a look=20
under a few different pianos and think about what you see and how=20
they sound.

By the way Terry, congratulations on your new venture into belly=20
work. Looking good.

Ron O.
--=20
_______________________

OVERS PIANOS - SYDNEY
Grand Piano Manufacturers

Web: http://overspianos.com.au
mailto:info@overspianos.com.au
_______________________
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