Case separation or delamination question

[Delwin D Fandrich]

----- Original Message -----
From: "David Skolnik" <skolnik@attglobal.net>
To: <pianotech@ptg.org>
Cc: <caut@ptg.org>
Sent: March 29, 2002 4:15 AM
Subject: Case separation or delamination question


> Dear list -
>
> What is your approach to dealing with separation of the inner and outer
> rims of pianos such as Steinways?  How evident does such a condition have
> to be to be of concern (any) to you when rebuilding?  I suppose my
question
> is directed primarily towards rebuilders, but don't let that stop you if
> you have a strong opinion. I attempted to look this up in the archives but
> found nothing of relevance under 'delamination' or 'case
> separation'.   Also, I wonder how often you see this condition in new
> pianos (only a few years old)?    Thanks -
>
> David Skolnik
> ----------------------------------

Rim delaminations are usually not a matter of great concern--at least not
structurally--unless the delamination is evident for some considerable
distance or the affected area is expanding.

That's the broad, generalized, answer. More specifically it's going to
depend on the piano--particularly on how the rim was constructed--and on the
location and type (or cause) of the delamination.

With the so-called one-piece rims (Steinway, Baldwin, etc.) the usual
problem is traced to the difficulty of maintaining a proper glueline
thickness between the inner rim veneers and, sometimes, the lower half of
the outer rim. This includes the glueline between the last inner rim veneer
and the first outer rim veneer. If the inner rim veneers are just slightly
on the thick side there will be excessive glue squeeze-out and the danger of
a starved glue joint exists. If the veneers are just slightly on the thin
side the glue joints will be too thick. Since the adhesives used are very
poor gap-fillers the resulting adhesive bonds will start out weak and will
further deteriorate over time. But, there is a lot of glue surface involved.
Any visible problem from either situation, unless it is severe, will not
show up soon. Veneer separations a few years or decades down the road are
more likely, assuming any problem develops at all. There is far less stress
on piano rims than is commonly thought.

With the now much more common style of rim construction in which the piano
is basically built on a separate inner rim with the outer rim being added
down the line somewhere, the most common problem involves getting the joint
between two rims just right. If the two rims do not match perfectly, or if
the joining operation is not done properly, there can be a gap between the
two rims. If a manufacturer knows the fit between the two is really bad,
numerous screws will sometimes be used to help ensure a good mechanical
joining of the two. Any remaining gap is either be filled or tolerated.

With both types of rim construction, if the presses are RF heated and
something goes wrong with the RF generators, there can be general adhesive
drying and/or curing problems . In these cases the adhesive can dry but not
cure and subsequent wide-spread delaminating can occur. This would be a rare
kind of failure to find in the field on a finished piano.

Structurally and acoustically there is no advantage to either style of rim
construction as long as each process is done reasonably well. A glue joint
is a glue joint and it matters not whether the entire rim is formed in one
pressing or in two pressings that are later glued together. Having worked
with both I now have a preference for the so-called two-piece rim
construction. The resulting rim is at least as strong and the piano is much
easier to build accurately.

I'm assuming your question applies primarily to pianos that have been around
for a while. In all of the pianos I've encountered with varying amounts of
rim separation I've only encountered one that I know affected tone
performance in any way. In that piano the separation was on the straight
bass side and went nearly the full length of the side. The outer rim was
completely separated from the inner rim for most of its length. The tenor
section sustain was a bit short, though not dramatically so. Once the two
components were glued back together (with epoxy and a few screws for
insurance) sustain did pick up a bit.

In most cases I wouldn't be overly concerned about the small areas of veneer
delaminating often found in otherwise serviceable pianos. Keep an eye on the
area involved but, unless the delaminating is spreading, it's probably not
going to cause any real problems.

As part of the rebuilding/remanufacturing process the rim should be examined
for potential structural problems. If, during this examination, any rim
delaminating is found the gaps are filled with epoxy. For this we use WEST
System type 105 epoxy resin with type 209 extra slow hardener--I want as
much working time as possible. The liquid epoxy is simply flowed over the
affected area and worked down into the voids as much as possible. If the
voids are quite wide a bit of wood flour is added to toughen it up a bit.
The area is checked from time to time and more epoxy is added and worked
into the voids until they stop accepting the stuff. Unless the gaps are
fairly wide--1 mm or so? I've not measured--we do not clamp them back
together. Sometimes clamps and straight cauls are used if the outer rim
bulges out as a result of the delaminating and we're trying to make the
straight side straight again. If we do clamp, it is done lightly, epoxy
likes a nice, thick glueline. When the epoxy has cured we scrape and/or sand
back down to the wood and paint per our normal practice.

Delaminating rims in new pianos is another issue. I rarely work on new or
nearly new pianos unless one comes to us for a new, modified board. My
advice would be to inform the selling dealer and/or manufacturer.

Regards,

Del