Bridge Doglegs, was: Spreadsheet info / Jason Kanter

[Frank Emerson]

For a vertically laminated bridge, in many cases, you simply cannot bend it
that sharply.  OK, I should know better that to use the word, "cannot."  To
some, on this list, that constitutes a challenge to prove me wrong, so I
will qualify this by saying that within a given manufacturer's standards,
there is a limit to how sharply it can be bent.  Factors determining this
include, the thickness of the laminations, the material used for the
laminations, the moisture content of the material, the width of the panels
to be bent (and therefore the number of bridges that will be cut from one
blank pressing), etc.  The more one tries to push this limit, the greater
the risk of voids in the glue lines at the bends, and the greater the
rejection rate.

For a cut bridge, the sharper the curves at the dogleg, the more material
is wasted, in a production environment.  The sharper the curves, the less
continuity of grain along the length of the bridge.

Of course, if one were going to cut over halfway through the bridge for
plate clearance, or put a finger joint at the dogleg, I don't suppose it
matters much how sharp the dogleg is.  With both a cutout and a finger
joint, it might as well be two separate bridges. 

I am not entirely sure that there might not be a good acoustical purpose
served by minimizing the dogleg.   I am getting into dangerous territory
here, since I have no study to point to which would support this argument. 
There must be some reason why the treble bridge is commonly undercut to
make the gluing surface with the soundboard a smooth(er) curve.  I'm
thinking that the more the long bridge snakes along the soundboard, the
more its capacity to transfer its energy to the board is inhibited. (Flame 
suit on.  Go for it!)

Frank Emerson
pianoguru at earthlink.net


> [Original Message]
> From: Farrell <mfarrel2 at tampabay.rr.com>
> To: Pianotech List <pianotech at ptg.org>
> Date: 12/19/2006 7:37:36 AM
> Subject: Re: Bridge Doglegs, was: Spreadsheet info / Jason Kanter
>
> To what advantage is minimizing the bridge dogleg? If the bridge needs a
30 
> mm offset to maintain target speaking length progression, then why not
just 
> build the bridge with a 30 mm offset? What's the problem?
>
> Terry Farrell
>
> ----- Original Message ----- 
> From: "Frank Emerson" <pianoguru at earthlink.net>
> SNIP
>  > ...and to use other
> > tools to minimize the dogleg in the bridge. 
>
>
>