[pianotech] GH-1s

[Ron Nossaman]

On 12/20/2012 4:34 PM, David Love wrote:
> Yes, I understand that the cutoff makes for a smaller rib cross section but
> it's not without other consequences.  Why not reduce the rib to 550 mm.  You
> could reduce the cross section even further.  The tonal implications can't
> be ignored.  We can talk about physical structure and ignore subjective
> evaluation of tonal consequences but we are building a musical instrument,
> not a bridge to drive toy cars over.

We're talking load and rib sizing, or we're not talking.


> Your question for comparison is a bit in isolation and so it's hard to be
> very precise because I don't approach it this way but I will try just for
> comparison sake.  Just so we are on the same page I'll assume you did these
> beam calculations with MOE for sitka spruce.

Isolation means nothing. It's a simple straightforward no bullshit, no 
diversion rib loading calculation. Yes, Sitka at 1570000 psi.


> I actually use 1.5 degrees, not 1 degree, but since you calculated the rib
> dimensions based on a load of 25 lbs I'll use that.  Twenty-five pounds load
> on a rib is very low to me.  If I extrapolate that out and use the total
> load on a board as I would load it then that would mean that the board would
> have some 36 ribs!  Approximately 900 lbs divided by 25 lbs gives 36 ribs.
> Even at 1 degree it would be about 600 lbs and use 24 ribs (I'm using 35000
> lbs total tension, I don't remember what a Steinway B actually is off the
> top of my head).  First of all, I wouldn't build something like that.  Nor
> do I target a specific certain percentage for deflection which is a somewhat
> arbitrary number depending on the amount of crown you have as you pointed
> out. My approach is a bit different.

That 25lbs is from bearing calculations of unisons actually being 
carried by the rib (one of 18), not an arbitrary equal dispersion. Ribs 
in actual pianos aren't equally loaded, for your apparent information.


> But if I had a rib as you describe and wanted a 50% deflection then my 770
> mm rib with 9M radius that needed to support 25 lb of calculated load would
> measure more like 15 mm wide by 16 mm high, roughly.  That's 24 ribs at 1
> degree or 36 ribs at 1.5 degrees for the whole piano.  Of course, I'm using
> fixed end formulas, not simple ends formulas.

That's a start, but you said you don't use tight radii, nor cutoff bars. 
That's what I would do. I asked for your claimed real approach, full 
length with a more conventional bigger radius. What would your sectional 
dimensions be for a 1090mm rib at a 16M radius, for instance?
Ron N