Do you dry the ribs, along with the board, prior to gluing ?

[Richard Brekne]

Grin... Come on Thumpy... if you are going to be a list heretic you  
have to do better then this.  You seem to be lacking knowledge as to how 
to figure downbearing  and how to calculate how rib strengths    This 
kinda puts you at a disadvantage in your task.  You HAVE been following 
these discussions on soundboard construction yes ?  A couple comments 
interspersed below to perhaps help get you started.


        > jobs you can easily experiment with then I'd say
        > renew the glue joint
        > between ribs and soundboard, f


   What do you mean by that ?  Dribble thin CA along
   them, and watch it soak in ???

No... I mean re-glue the ribs to the soundboard where they have 
separated.... before doing anything else since you already have the 
panel dried and jacked up.


            Figure how much new
        > support you think you
        > need from rib extenders and make them to appropriate
        > dimensions,


   And how do I figure that ? I was just thinking more in
   terms of increased crown/ dowbearing, created by
   laminating maybe a  3/16 strip to the back of the
   current ribs. How can I be more scientifical about
   determining its actual dimensions ?
Grin... is this a serious question ?  How can you be more scientific 
then slapping on a 3/16 strip to the back of the current ribs ? I think 
the question is rather how can you be less scientific here... come on... 
you're pulling the proverbial leg here yes ?

        jack up
        > the soundboard a bit and glue them on.



   Well, that's one of the fun parts about this system. A
   hardwood board is screwed along the back of the piano,
   with threaded inserts right above where the ribs cross
   the cracks. Bolts are screwed through it to really
   jack the board up, RIGHT UNDER the crack being worked
   on, and then it's moved to the next crack. When gluing
   laminations to the spine of the extant ribs, these
   "board and bolt" jigs would work terrifically, to
   REALLY jack the board up in a  bowed-out condition,
   while the glue cures, and then when it's
   removed-presto! - You've got a  board with lots of
   bearing and crown ! ( And I still like the bamboo
   skewer idea,  to make double extra sure nothing ever
   "slides"  ! They're quite strong, only 1/8" diameter,
   and already have "fluting ".  )

These are part of the recrowning system your mate told you about ? 
Gluing rib extenders on in the way  I think you just described would be 
essentially the same thing as pressing a panel into a curved caul... the 
the basic premise is good ... if I understand you correctly.


   My only concern would be in putting TOO MUCH crown, or
   stifness, into the board, thereby wrecking the tone in
   some way ?  Is that a  reasonable fear ???  How do I
   calculate "how much " ? I would imagine, with ribs
   thus laminated, they'd keep a  lot of their arc, once
   the jig was removed. ( As long as the glue cured fully
   . ) And that they'd be more resitant to downweard
   deflection. ( My 1899 Knabe has laminated ribs, and
   plenty of crown, still ! )

Its not about crown... its about crown support... crown strength... load 
bearing ability... whatever you want to call it... and about how much 
you load the darn thing to begin with.

        Since you no doubt have this thing strung
        > down and the plate off
        > you should be able to get a very reasonable
        > estimation of the
        > re-finished assembly strength.


   Yeah ? Like how ? I'm totally  "in the dark' as to
   what you're talking about doing here. ( Sorry. )

Find out how strong it is now... how much weight it takes to deflect it 
so and so much.  Compare that to what downbearing amounts you expect to 
have, then figure how much added support from your rib extenders you 
will need to do the job... with that figure you can decide rib extender 
dimensions. None of this takes into consideration how much mass each of 
these composite ribs will have when all is finished... but I get the 
feeling this is complicated enough already  :)



   Figure how much down
    > bearing you are
    > going to end up with and make sure the thing can
    > hold it.

   Sure.  And how much do I want ?  And How  do I figure
   if it can "hold it ?"

Take your stringing scale... use the string tensions, speaking lengths, 
back lengths, and deflection angles at the bridge.  That gives you 
downbearing.  You need the panel to hold up against this amount... 
actaully you want it to be able to hold up more then this amount.  
Perhaps to be safe you might decide to try get the thing to deflect only 
50 % of its unloaded crown.
        You can easily
        > enough work all this into your scaling spreadsheet.


   Sorry. Don't  know how that relates, either ? Will you
   please "clue me
   in " on this ?

You use the string data in a scaling spreadsheet to calculate the amount 
of downbearing for all the strings for whatever offset angle you decide 
on for any given string.  Basic trig... several articles in the journal 
through the years...  I just had a related piece a few months back.  You 
can also combine with a spreadsheet that does rib bearing capacity 
calculations.... If you are good with Virtual Basic I suppose you could 
get real anal and do some cool graphics displays showing a given 
assembly's amount of deflection for a given downbearing load. I'm afraid 
I'm barely sufficient with Excel myself.


        > All this said.... its probably easier and better to
        > just knock out the
        > old panel and put in a new one.

   I dispute that. I'm still one of those "politically
   incorrect " types who believes that old wood is more
   resonant than new, and if you can get the desired
   crown back into an old board, it's better !!!!!!!!

Big Grin... hear here now Thump my man... HOW on EARTH can you have even 
the slightest solid groundwork for such a belief if you don't know how 
to figure downbearing and at least come up with a good guestimation of 
how load  much your soundboard can take ?  You can get tons of crown 
back into an old board that wont hold jack diddly... or just a little 
that will hold a lot...  whatever resonant vibes your old wood may 
have..... and thats just scratch'n the surface of the whole problem really.
You need to get someone off list to help you go through this step for 
step....  or just shoot in the dark with your 3/16ths .....   I'd 
suggest the former as you'd learn a lot on the way.  Good luck.

Cheers
RicB


   Thump
    >
    >