Spurlock shimming method.

[Overs Pianos]

Del Fandrich wrote:

>. . Given a crown radius of 18 m the
>difference between the length of the arc and the length of the chord of a
>soundboard rib 1200 mm long is only 0.21 mm. In other words, assuming that
>the rib is made of some perfectly rigid material -- obviously not wood of
>any kind -- it will only have to deflect the rim by 0.21 mm to go from a
>fully crowned condition to a fully flat condition. This also, of course,
>assumes that the rib/soundboard panel is not going to distort or twist in
>any way whatsoever. In other words, a completely impossible situation.

Agreed.

>. . . The rims you are using in your piano are made by Samick. You can distort
>this rim by leaning against it.

And similarly that of any other piano you care to lean against. I 
first noticed this phenomenon when setting the down bearing in a 
concert piano (a Hamburg Steinway D as it happened - we've done quite 
a few over the years), and yes I understand that the D has one of the 
most rigid rims in the business.

>How can anybody really believe there is
>enough rigidity in that rim to resist that 0.21 mm expansion?

Your criticism of the Koreans for using 'select hardwood' is well 
known, and I can only concur with your opinion. However, that rim to 
which you refer has an inner rim thickness of 45 mm, with an outer of 
26, and while the standard Samick grand piano rims are manufactured 
with substandard less dense timbers, the WFG series grands (according 
to the Samick website) use maple. It is probably reasonable to assume 
that maple continues to exhibit the same density as found when used 
by other manufacturers, when Samick use it for rim construction also.
We ordered the 225 Samick cases we have used to date with maple inner 
rims and belly rails. We got a maple belly rail for piano three 
(which will be displayed at Reno) but the inner rim is still made 
from ordinary stuff. I must admit I was pretty annoyed about not 
getting a maple rim for 003, especially when the WSG pianos have it. 
I can assure those of you who may be doubting Thomas' that our future 
grand pianos from no. 004 inclusive will have maple rims or better. I 
can make this assurance because if we can't get the cases made with 
maple rims, I am quite prepared to lose a years production while I 
get my own 225 design case and plate into production (which is drawn 
up but without tooling - bending bucks etc.), in which case we would 
not use maple for the rims (which has a density of around 0.7 gr/cc), 
we would use an Australian southern Beech (Antarctic Beech) with a 
density of 0.74 gr/cc.

>And remember,
>this is the most extreme deflection required to lose all crown assuming a
>1200 mm rib -- a rather long rib in most pianos. And assuming a perfectly
>inelastic rib and a perfectly inelastic soundboard panel. And assuming no
>distortion within the panel. With most ribs and most soundboards in most
>pianos the crown radius -- as installed in actual pianos and not in
>somebody's dreams -- is going to be considerably less.

I also have done the maths, and I understand where you are coming 
from. I can assure you I'm not dreaming. I just chose to use a 
production case and plate to get into manufacturing after fifteen 
years of grand piano rebuilding. Using someone else's case and plate 
seemed like a good way to achieve it without going broke, since it 
has not been my style to rush around obtaining grants from various 
institutions, or working from within the relatively comfortable 
surroundings of an established piano factory, as some successfully 
have done. I am the first to admit that I am relatively inexperienced 
when it comes to the finer points of sound board technology. But I 
don't plan to remain so for very long.

>Hence the difference
>between the chord length and the arc length will also be considerably less.
>Remember also that a fair number of these ribs terminate on the bellyrail,
>all of which are notorious for their flexibility.

But need not be if they were fixed at say two points along their 
length (as in Welmar pianos) to the plate and were made of suitably 
dense timber. Furthermore, many manufacturers seem obsessed about 
attaching the plate and belly rigidly at the bass treble cross, when 
I can't help thinking that the next string break up might well 
benefit by a similar attachment system. After all, so many on this 
list rightly bemoan the lack of rigidity in the 'killer octave', 
attaching the plate to the belly at around C52 would I suspect go a 
long way towards un-killing the killer octave.

>The best argument given so far discounting the whole notion of the rim
>supporting crown is given above where you point out that when you lean
>against the rim of the piano the crown of the board changes. And this is the
>same rim that is supposed to be supporting crown by virtue of its absolute
>rigidity?

Sure, but the words 'absolute rigidity' are yours not mine. I too can 
understand that a rim may give way, especially since most pianos are 
ineffectively cross braced. But an understanding of simple 
engineering principles must lead me to suspect that an arched sound 
board which has not gone flat and remains attached to a substantial 
rim must be getting, OK just a tiny bit of support. While I don't 
doubt your experience with sound board technology, you must concede 
that however weak the spruce and low the arch of the panel, it still 
has to be pushed and wont just fall straight - at least not in the 
short term.

>Have you ever heard the expression, "missing the forest for the trees?"

Have heard the expression once or twice. Even found myself uttering 
it from time to time.

>Well, this is one of those situations. We seem to want so badly to believe
>something other than the plain truth of the thing that we get bogged down in
>all this minutia which is of absolutely no consequence in any kind of real
>world piano.

Finding myself wanting to believe in something other the plain truth 
doesn't hold a great deal of appeal to me. But you must concede that 
for any discipline to progress it is sometimes through the 
investigation of 'minutia' that minor advances are made, and 
unfortunately many 'advances' are 'minor' in nature.

>In the meantime, of course, time marches on and the piano
>continues to languish as a has-been instrument. Argh!

Not in my workshop if I can help it.

Regards,

Ron O