Case separation or delamination question

[David Skolnik]

Thanks Del & Zen for your replies. First, a bit of an apology. I cross 
posted to the CAUT list because I suspected that there are some people who 
are on there exclusively, remembering afterwards that I, myself have 
sometimes found it confusing when the same thread subject is being carried 
on simultaneously on both lists, sometimes with cross posting, and at other 
times on only one or the other.  I considered forwarding the CAUT responses 
to this list & visa versa, but suspect that will just make things worse, 
so, for now, if you're interested, there are some other responses on the 
other list as well.

The piano in question is an old Steinway C (?) 85 note from about 
1883.  (There was either a recent posting or it was on someone's web site 
that I saw an excellent listing of old models and dates.  I can't find it 
at the moment).  The delamination between inner and outer rims goes 
completely around the perimeter.  The visible gapping is generally from 1 
to 2mm.  I only had a flat steel handled upright mute (.5mm or .020") to 
use as a feeler gauge & it tended to insert between 1 to 2 inches throughout.

The piano was recently rebuilt (within the last year and a half).  There 
have been significant tonal deficiencies, especially in the 5th and 6th 
8ve.  From the 7th rib up there is no apparent crown.  I didn't notice the 
delamination when the piano first came back, but, in spite of a few months 
out of the year of rather low humidity (20%), I doubt that such a degree of 
separation would have happened in such a short time.

The main question for me is, what design parameters are impacted, and to 
what degree, when there exists a significant amount of inner rim -outer rim 
separation of a unified rim design.

At 09:35 AM 03/29/2002 -0800, Del wrote: (Edited)

>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.

>There is far less stress
>on piano rims than is commonly thought.

What are the sources of stress in a single rim construction? The initial 
bending creates the classic tension/compression stress.  Spreading the arms 
to fit the pinblock relaxes some of that stress, but stresses the cured 
glue joints. Some stress is transferred from the strung plate. and perhaps 
some outward stress from the compression of the soundboard.  Some of the 
stress is internal, some imposed.  Would the acoustical properties of the 
rim change over time, as the internal stress dissipates?

>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.

>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.

So, what purpose does the outer rim serve, in a Steinway?  Would you 
suspect any discernable difference between a Steinway built in the 
traditional manner and one constructed with a 2 part rim?  For that matter, 
when did Steinway begin unified rim construction?

>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.

In an older instrument such as the one I have described, I would assume 
that most, if not all of the original internal tension has relaxed.  Unless 
the outer rim contributes to rigidity of the soundboard mounting, affecting 
crown and energy reflection,  the only reasons I can see addressing rim 
separation would be either cosmetic, to prevent potential transient 
vibrations, or to keep it from getting worse.  Have I misunderstood or 
misstated your position, or does this correctly reflect your thoughts?

Thanks -

David Skolnik