structural members

[Delwin D Fandrich]

----- Original Message -----
From: <ANRPiano@AOL.COM>
To: <pianotech@ptg.org>
Sent: September 06, 2001 7:54 PM
Subject: structural members


My questions are:
>
> 1) What kind of strut organization is most desirable?  Is a fan better
> generally or worse than a post and beam?  How would I determine which is
more
> appropriate?

The ideal belly bracing system should do two things:
    1)    It should stiffen the rim (particularly the straight, bass side)
and the belly rail (especially the upper tenor and treble region).
    2)    It should provide a termination for the nosebolts which
mass-couple the plate down to the beams providing stability and damping to
the plate.

The fan arrangement does an excellent job of stiffening the belly rail at
the bass/tenor break region (usually), which is of very little value unless
some of the stress from the string load is coupled down to this point by
some kind of extension of the plate. If possible, consistent with the
locations of the existing nosebolts, I would develop an 'H' arrangement with
at least one crossbeam extending over to the straight (bass) side. The
longitudinal braces would be roughly perpendicular to the bellyrail and
would butt up against the bellyrail at approximately the bass/tenor break
and approximately the tenor/treble break. I would also have one more brace
running from the treble inside curve forward to the bellyrail about 1-1/2 to
2 octaves down from the treble or at approximately the 1st treble/2nd treble
break. Beyond this, just make sure there is something where the each of the
nosebolts expect there to be something. Remembering that often the nosebolts
went into a block bolted/screwed/glued to the side of a bellybrace.



> 2) What is the best means of attaching the struts?  Tongue and grove,
dowel,
> or . .?

We do quite a lot of this and generally just butt them up against the rim
and/or bellyrail. Once the brace is nicely fit to the chosen spot we
saturate the endgrain with epoxy and allow it to soak for a few minutes,
recoating it as the epoxy works its way in. When no more will saturate the
endgrain of the new brace we coat it with an epoxy/woodflour matrix and butt
it in, blocking and lightly clamping until the epoxy is hard. We then drill
two 1/2" holes in at a 45º angle from the top and two from the bottom and
drive in fluted dowels. The dowels are simply glued.

If there is anything special (like the bottom plates typical of S&S
bellybraces) we duplicate it just for looks.



> 3) Should the termination points of the struts correspond with the plate
> struts?

Only if there are nosebolts there. Remember, these are simply to stiffen the
rim and bellyrail. They are not string load carrying devices.



> 4) What kind of issues are most critical in determining the cross section
of
> the new beams?

We tend to duplicate the original unless there is some compelling reason to
deviate.



> I would like to attach all the nose bolts to a beam, since I am sure in
> original design of the piano they were there.  I will gladly remove and
> change the one original beam if it doesn't fit the new configuration.

You probably won't have to. I suspect that at one time there actually were
braces under there but, as the manufacturer sought ways of reducing his
costs they were removed.

What this sounds like is a running production change in which the changes
were made to the rim just before they ran out of the old-style plates. The
various workers each did their jobs correctly, but without effective
coordination from management.

Typically this kind of thing would be a 'matched quantity' change. That is,
existing inventories would be matched so that they would run out of all of
the affected components--in this case, the old-style plates--just as the
last of the old--style rims (those with all the bracing) came down the line.
The new plates--without the nosebolt holes--would then arrive just in time
to match up with the new rims not having all the bracing.

In this case I suspect there was at least one old-style plate too many. This
kind of thing happens more often than you might expect. We've seen it is
several pianos ranging from Emersons to Mason & Hamlin A's. (We have one of
these in the shop right now which had a nosebolt running down through a
plate brace with a nut on the bottom of the brace. No hole at all through
the soundboard and no brace down there for it to go into if it did go
through.

Regards,

Del