[CAUT] Restringing treble

[Bob Hull]

Questions about this theory: If the plate is able to
flex like this then why am I having the following
experience:

I have just done soundboard repairs on an older 5' 6"
Weber grand including coating the board with epoxy.
Instead of resting on dowels the plate sits on a
continuous ledge about 1/2 inch (12.7 mm) high around
the perimeter of the soundboard. In order to increase
the downbearing I have lowered this ledge to approx.
.42 (10.6 mm).  The db will still be minimal but I
don't want to overstress this old board.  Since it was
difficult to know just how this lowered ledge surface
would mate to the bottom of the plate,- where the two
would meet-, I used slips of paper between the bottom
of the plate and the top of the ledge (like when
bedding a keyframe) to feel where the two were
meeting.  I found there was a small gap between the
two -  enough to freely slide the paper strips along
almost the entire area(if the paper was .003 then the
gap was maybe .006 but I hadn't tightened the
perimeter screws yet. It did have contact with three
small areas.   Surely when I tightened the screws the
little gap would disappear  - right?, the plate is
somewhat flexible as you have been discussing -  but,
tightening the screws did not eliminate the gap or
change it as far as I could detect.
    I lowered the places where there was contact 
which still didn't improve the mating of the plate and
ledge.  So, I created highpoints or resting spots
(using WEST epoxy)on each side of each screw as if it
was sitting on really short "dowels".  Protecting the
board and plate with wax paper I lowered the plate
back down and tightened the screws to make the epoxy
fit the gaps - - like pinblock final fitting. 
Of course, if I remember correctly the plate is
thicker around the edge and maybe it's elasticity is
too limited there to flex.  The plate as a whole is
more capable of flexing/bowing because it is a lengthy
span which is anchored around the perimeter and at
tiny nose bolt locations. The original design, if the
plate and continuous ledge were well mated, seems like
it would have a different effect on plate behavior
characteristics than a plate that rests only on dowels
or lag screws. 

A long explanation to ask "Why didn't the plate flex
down when the screws were tightened?" 
Also, what other/better ways would you have approached
this plate height situation? 
  
--- Ron Nossaman <rnossaman@cox.net> wrote:

> 
> >It seems to me that the following may  prove this
> theory.
> >
> >The next time you experience a broken string,
> measure the pitch change on 
> >adjacent strings/notes. Then press down on the
> bridge about 7 lb. worth. 
> >If there is no effect on the pitch on these
> adjacent strings, you will 
> >know it is not the downbearing change on the bridge
> causing the pitch 
> >change. After the new string is installed, check
> the adjacent strings again.
> 
> If someone who uses an ETD tries this, please post
> the results to the list.
> 
> 
> >Do you think this will prove the point? I've not
> done this, but I will do 
> >this the next time the situation occurs. This has
> been enlightening, 
> >because I've always heard that pitch change takes
> place due to the change 
> >in downbearing on the bridge and soundboard.
> >
> >Sincerely,
> >Gary Mushlin, RPT
> 
> All of us have always heard that, but I don't see
> much indication that it's 
> true.
> 
> Ron N
> 
> _______________________________________________
> caut list info:
> https://www.moypiano.com/resources/#archives
> 





		
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