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In a message dated 1/20/2002 6:41:51 AM Pacific Standard Time,
mfarrel2@tampabay.rr.com writes:
> Terry
>>>Welcome to the insomnia club. Considering all the variables in the
always in flux soundboard system I've always thought that setting bearing to
the degree you are speaking ofis a bit like making a jello foundation for a
house. Just when you thought you had the right consistency poof it wiggled
and the house fell over.
Well it's not quite as bad as all that
>
> I have always been curious about the soundboard pre-stressing method of
> targeting downbearing, but when I ask how much to push the soundboard down,
> I get answers like: "enough", "not too much" and the like. The idea of
> getting a feel for how much the soundboard will deflect under load I should
> think would help target proper downbearing Now I see here we are using some
> numbers. This is a good thing. You say David Hughes deflects the board 3 mm
> at the center strut. You state that you drive wedges under each strut. How
> much do you deflect the board at each strut?
>>>>The short answer is after driving the maple wedges in, readings of
deflection will be appox.3 to 3.5 at the central strut about 2 ish on the
next treble strut and 1 to.05 on the top. The lowest tenor strut can be
forced lower than is needed and should not be over driven. It's value will be
in the 2 mm range. But hey if you don't want to take my word for it e- mail
Dave hughes at davehugh@msn.com and ask him.
Terry, save some time and read John Hartman 'effects of downbearing
on tone' aug,sept oct nov. 1996. Very good reference material. The last
article will give you some numbers that I can see a person like you is ready
to digest. I have posted a description of this in the last year on this list.
>
> Now the other question I have is that I assume the reason one would
> pre-stress the soundboard is to incorporate into your work how much the
> soundboard will deflect under load.
>
>>>>>>.. Yes an approximation
But if you deflect the soundboard 3mm or whatever, wherever, for any given
> soundboard, what does that do for you (i.e., you are pushing a stiff board
> 3mm down, and you would be pushing a highly flexible board 3mm down - under
> strung conditions, obviously the flexible board would deflect more under
> final strung downbearing)?
.>>>>>> Ist question. Your making it stiffer and changing the impedance
.>>>>>Yes but for the sake of discussion lets stick to newly crowned boards.
The same principles can be modified for other situations. Rib crowned boards
with either sugar pine or spruce ribs and duplicated to original rib
heightswill result i a stiffer board than the old compression crowned boards
and the amount they compress is fairly predictable.
>>>>>>>> Remember jello? It moves. So does a new unstrung soundboard. Up
And down with moisture content. So at what point in the moisture content
cycle are you going to set your bridge heights/downbearing. More insomnia
material.
You could simply calculate the needed angles without pre-stressing the
board.
> Now if you could pre-stress the board with downward pressure approximately
> equal to that of the final string downbearing in the various regions of the
> scale, then we would be truly simulating the soundboard's reaction to the
> strung-up load and accurately calculate our desired string downbearing
> angles, etc. Of course to do this we would need some sort of pressure
> gauge/device.
>
> >> Terry I know Steinway doesn't carry much weight with you but they've
> done it this way for a hundred fifty years but so has mason and others
>>>See Bob Hofs article on this last year he uses go bars off the Ceiling.
The down side to that is I can't feel what go bars are doing in the same way
as I can with my fist.
>> With the maple wedges I insert them between the struts with the left
hand as I pound with my right fist on the bridge top. As the board sinks to
appox. 3 mm it gets so stiff it feels like your pounding on a gym floor. Or
you pound till it feels real stiff It's an aquired feel that's not difficult
to get the hang of. Repeat at each strut.
> What about a rig similar to a pneumatic rib clamp. Just use the half with
> the fire hose. Clamp it to the rim above the bridge, inflate, and there you
> go with measurable pressure applied all along the long bridge in much the
> same manner as downbearing would be once the piano is strung. You could
> also use four segments of fire hose to apply appropriate variable pressure
> to each of the four sections (and one on the bass if you want to do that).
> The result would be a board stressed in very much the same manner as it
> would be after stringing. Then you could set your downbearing exactly where
> you want it, armed with the knowledge of exactly (or there abouts) how much
> the soundboard will deflect!
>>>>Dave Love was right, no access to the bridge.
>
> So now, readers..........you are thinking one of two things: Either Terry
> Farrell needs to get his head screw on properly, i.e. it's a dumb idea, or
> it sounds like a great idea, now go try it Terry and write us back. So what
> do you think?
>>>Your doing some good thinking. no worrys you're on your way
> Maybe it is the case that with a given soundboard construction, the boards
> are consistent enough to yield predictable result when pre-stressed 3mm or
> whatever. Is this the case, and thus would yield a more accurate
> pre-stressing a waste of time?
>>>>This what I'm gettin at
> I guess I'm just thinking and probing for information. Any input would be
> appreciated. I realize the thing to do is put in a couple dozen boards, try
> some different methods, and see what happens.
>>> This helps a lot. Of course don't forget the fun factor. I hope this is
helpful verses annoying.
But boy oh boy, that will be years, and I would fear, some tears. I'm just
trying to
> arm myself with as much info a possible before I screw up too darn many
> pianos.
>
> Terry Farrell
>
>
> >> ----- Original Message -----
>> From: <A HREF="mailto:Erwinspiano@AOL.COM">Erwinspiano@AOL.COM</A>
>> To: <A HREF="mailto:pianotech@ptg.org">pianotech@ptg.org</A>
>> Sent: Sunday, January 20, 2002 1:07 AM
>> Subject: Re: Baldwin accu-hitch pins
>>
>>
>> In a message dated 1/19/2002 9:15:16 PM Pacific Standard Time, <A HREF="mailto:davidlovepianos@earthlink.net">
>> davidlovepianos@earthlink.net</A> writes:
>>
>>
>> >>> Subj:Re: Baldwin accu-hitch pins
>>> Date:1/19/2002 9:15:16 PM Pacific Standard Time
>>> From:<A HREF="mailto:davidlovepianos@earthlink.net">davidlovepianos@earthlink.net</A>
>>> Reply-to:<A HREF="mailto:pianotech@ptg.org">pianotech@ptg.org</A>
>>> To:<A HREF="mailto:pianotech@ptg.org">pianotech@ptg.org</A>
>>> Sent from the Internet
>>>
>>> David
>>
>> David Hughes and I both drive wedges in under each strut to compress
>> the board along its entire span. We start at the central strut then first
>> and last capo then bottom strut. Then the dime quarter nickel business. I
>> use 2.5 mm top treble 2.25mm first treble an bout 2mmin tenor tapering to
>> 1.5 or so down low on tenor. Bass is set with about 1/2 degree at the top
>> tapering down to 0 at the bottom.
>> Pretty much the same.
>> Dale
>>
>> >>>
>>> Dale:
>>>
>>> My conversations and classes that I attended with David Hughes (if I
>>> remember correctly) led me to believe that he prestressed the board under
>>> the central plate strut by 3 mm and then set the bearing dime, nickel,
>>> quarter, in low tenor, mid-range, treble, respectively. That seemed to
>>> pretty much be his method without additional measurement. I'm sure he
>>> arrived at this method by much experience, but he didn't seem to sweat it
>>> beyond that.
>>>
>>> David Love
>>>
>>> >>>> Dale:
>>>>
>>>>
>>>
>>
>
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