laminated ribs

[Greg Newell]

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Dale,
         Interesting observations! I have one of my own if you will indulge=
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me. If as you pointed out that the RC&S assembly should very easily survive=
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are we loading them enough? My thoughts go along the lines of a superior=20
assembly still acting as an opposing (stronger) spring with the same load=20
as before. I don't have a full grasp of all this stuff yet but it seems to=
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me that if you change one system you have to change them both, no? The=20
opposing string bearing load should be correspondingly more I'd think.

Greg Newell



At 11:04 PM 2/18/2006, you wrote:
>   Ok, now this is an interesting discussion.  Admittedly not being a math=
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> guy I'm still interested in putting some numbers on some scales of things=
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> I've seen as a bench marks for comparison.
>    Let's just take one case I have  first hand knowledge of.  I rebuilt &=
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> 1960 Stwy L 3 years ago that lived in a Fresno area church from the=20
> beginning of it's creation to the present so it has survived wonderfully=
 well.
>   I was keenly impressed  by the balance of sound, both in power=20
> &  sustain.  I measured the bearing with a lowell gauge & though I don't=
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> have numbers any more to give you my recall is that the top capo had over=
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> 2 degrees of deflection & the 2nd capo  about 2 or more &  the middle=20
> was  1 1/2 degrees tapering down to 1/2  in the bottom & the bass had=20
> positive but minimum bearing as it should be with a cantalever.  The=20
> crown string stretched across the boards underside revealed lots of=20
> residual crown in the strung condition & more than any other C.C. board=20
> I've ever seen up to that time.  All that to say it was in my opinion a=20
> text book Steinway/belly  set up both in terms of crown &=20
> bearing.   These are IMO the kinds of observations that  are important to=
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> make when we find something that is working really well.
>   The Stwy L scale as I recall has an average treble tension at 160 lbs=20
> per string. It is obvious to see that the majority of the bearing=20
> pressure on the long bridge is increasing  gradually the higher up the=20
> scale we go.
>   So knowing all of the above, what is the equation that will calculate=20
> an approximate string bearing load under the conditions I describe?
>   If it's the one- 40th rule for simplicity then  40 divided into  160=20
> strings  equals 4 pounds per string. Let's remove most of the bass=20
> strings from this equation for now, since theoretically there isn't much=
=20
> bearing there & we have approx. 160 strings times 4 pounds equals 720=20
> lbs. add in say 80 lbs for the bass & it's about 800 total pounds give or=
 take
>      There is a much more accurate & glamorous formula for this but I=20
> dont' have it at my finger tips.  If the scale tension averages 180 lbs=20
> per string then we're talking 4 1/2 pounds per string which bumps total=20
> bearing load up another 100 ish pounds.
>   My point in all this is that if we are using stronger engineering=20
> materials & principles which building better stronger rib structure,=20
> which we are, then surely our rib crowned & supported boards will survive=
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> as well & IMO longer than this example of a C.C Steinway L  I cited above
>    Don't you think?
>   Dale Erwin
>
>Consider a basic scale of moderately high tension. Say 40,000 lbs.=20
>overall. With this string tension 1,000 lbs of string down force equals=20
>2.5% of scale tension. That is quite a lot considering that most companies=
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>are claiming string down force more on the order of 0.5% to 1.5% of string=
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>tension (which would be 200 to 600 lbs). I thought I was setting my=20
>initial string down force pretty high at around 1.0 to 1.5%. I don't like=
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>thinking about what I'd be doing to a board loading it up to 2.5%. I can't=
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>imagine it being happy enough at that level to want to stay there.
>
>Del
>
>

Greg Newell
Greg's piano Fort=E9
mailto:gnewell@ameritech.net=20
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