Curve on Bridge Bottom

[Erwinspiano@AOL.COM]

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In a message dated 4/29/2002 8:34:53 PM Pacific Standard Time, 
RNossaman@KSCABLE.com writes:


>                  Terry and other interested folks

      While dry fitting a 1927 S&S L board today I was thinking about your 
question as to bridge curvature in the bottom of bridges so I thought I'd 
take a few measurements. 
   Prior to fitting the board in the case there is no evidence of crown along 
th bridge line.Non can be seen or measured. After dry fitting in the case 
with a few clamps it took on a great deal of crown along the bridge line. I 
was so take by this I took a number of digital photos with a long straight 
edge along the bridge line.There was probably a good 5/8ths of an inch  gap 
at each end of the straight edge. This crown was nice and hemispheical . Even 
taking into account the modest diaphramizing this is alot and obviously 
intentional. The rasten/inner rim is cut this way intentionally.
     The bridge ,not glued on yet was laid on the board in its location. 
Though it has some crown cut into it , it is not as much as the dry fit 
boards crown induced by simply clamping to the rim. Very interesting ehhh??
    Never the less to my mind the board will flatten out less with the bridge 
in a crowned configuration than a flat cut bridge, providing the bridge is 
glued to the board on a crowned suface as I described previously. However 
nominal this bridge support may be it has to resist bearing at least to some 
degree. I'll take whatever I can get.
>>>>>>>>>>>>>Dale Erwin>>>>>>>>>>>>>>

> 
> > Has a straight-bridger measured crown on an installed 
> >board without the bridge, and then measured it after the long bridge was 
> >installed? Does it not flatten the board a bit? 
> 
> I haven't measured after the fact, but I have set both a crowned and a flat
> bottomed bridge on a new board. There is not a heck of a lot of difference.
> The bridge is curved - that's CURVED. That being the case, a flat bottomed
> bridge will lay on a bridge just like a crowned bridge will. You won't be
> able to tell if the bridge lying on a board is flat or crowned by looking
> at it. Glued and screwed down to the soundboard, you still won't be able to
> tell. The only way this will come home to you is to do it both ways. If you
> think you can detect any difference between a flat and crowned bridge, go
> with the one you like best.  
> 
> 
> >Is some of the ribbing 
> >theory (tighter radii) designed to compensate for the small (??) 
> flattening 
> >effect of a straight bridge?
> 
> Not in the least. In my case, the tighter radii in the treble is intended
> to get some crown (and compression stiffening) under load in an area that
> has typically been deficient in both. I consider the flat and crowned
> bridges to be functionally equivalent.  
> 
> 
> >It can't hurt to cut a nice little curve into the bottom of a new bridge - 
> 
> >can it?
> >
> >Terry Farrell
>   
> Not at all, if you consider it necessary. 
> 
> Ron N
> 


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