[pianotech] was GH-1s

[David Love]

By half that, I mean that the pre load bearing at 1.5 degrees measured .75
degrees when it was loaded, just to be clear.

David Love
www.davidlovepianos.com


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of David Love
Sent: Friday, December 21, 2012 10:26 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] was GH-1s

Let me add that the rib after cutting and pressing had a 15M radius which
yields 5.5 mm of crown for that length.  A slight amount of compression
might add something to that.  The deflection on the rib for that load is 4.3
mm leaving about 20% of the crown.  In actual practice with the panel
installed and glued down the initial bearing of 1.5 degrees measured about
half that once strung and pulled to pitch.  That was right on target.  I
liked the sound too, but who cares about that.  I listen to the engineering.



David Love
www.davidlovepianos.com


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of David Love
Sent: Friday, December 21, 2012 10:11 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] was GH-1s

The premise of my load distribution is irrelevant in this case but it is not
false.  I believe your individually calculating the load of each rib based
on how the unisons fall is incorrect, that the bridge does distribute the
load.  How much bearing you set at one end or the other of the piano can, of
course, influence the load on each rib.  But you push the bridge down on rib
number 6 and rib number 4 deflects.  It doesn't do that just to be
respectful to rib number 6.  The issue, however, is how we're designing them
and the criteria we are using.  If I anticipated the same load that you did,
25 lbs, that's how I'd build it.  The premise of a rib in a piano that has
900 lbs of downbearing carrying only 25 lbs is a false premise unless you
have a whole lot of ribs or not much downbearing.    

You want something more similar that's real world.  Here's a rib in a piano
I built, Steinway A, with a small cut-off bar.  The rib is close in length
to your sample at 810mm in length.  The dimensions were calculated with a
load of 65 lbs.  The dimensions were 810 mm in length, 21mm w x 21.4 mm h. 

So let's put our thinking cap on, your slightly shorter rib carrying 40% of
the load that mine is in design, is still 5 mm taller than mine (the 1 mm
width difference doesn't make that much difference in load bearing).  What
more do you need to know?  You build yours heavier.  That, of course, is
your prerogative, but for me, that's too heavy.  If you don't think that
answers the question then you don't want to know the answer.    


David Love
www.davidlovepianos.com

>
> Yours:  25 lb load, 770mm x 20W x 26H, and a 9M radius
> Mine:   25 lb load, 770mm x 15w x 16h, and a 9M radius
>
> (for approximately 50% deflection)

I read that too, and it's useless because your rib loads are calculated on a
false premise of equal distribution of load along the bridge, and you went
with the cutoff. Size rib #6 of 18, at 1090mm long, or 999mm, or whatever is
your personal preference at whatever load you calculate and specify, and
I'll have something informational for comparison.
Ron N