Case separation or delamination question

[Farrell]

David wrote:
"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." 

This is a long post about rim delamination. If I understand you correctly, you are concerned that the rim delamination is causing the tonal deficiencies.

I'm no rim professional, but I suspect all you need to do with this rim is to flip the piano over and fill the little rascal gap with West System epoxy. I would suggest using it with no fillers at first so that the viscosity is low and it will flow deep into the gap. After it seems to be filling at the bottom of the gap, I would start squishing in West System thickened with a good high-strength adhesive filler.

Ok, so now you have the rim taken care of. Time to consider the cause of the tonal deficiencies.

You have a flat board with a dead treble. You mention the piano was rebuilt. New soundboard? Who made the soundboard? 

Original 119 year old Steinway soundboard? Yikes! If that is the case, I would consider focusing on the need for a new soundboard. (This kinda sounds like the situation to me!) Fully evaluate crown and downbearing over the entire soundboard to better understand your soundboard's condition.

Also, if you are replacing the soundboard, and if the rim separation extends completely through the whole (top-to-bottom) thickness of the inner rim, this will give you optimal opportunity to really get the gap completely filled with hi-quality epoxy.

Terry Farrell
  
----- Original Message ----- 
From: "David Skolnik" <skolnik@attglobal.net>
To: <pianotech@ptg.org>
Sent: Saturday, March 30, 2002 1:09 AM
Subject: Re: Case separation or delamination question


> 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
> 
> 
>