Ron, bass bridge undercutting... Ron & Del

[Ron Nossaman]

>Hi Ron, Hi Del,
>
>Yea, I think I'm getting the idea.  I sure appreciate your input.
>
>I was wondering, If you need to undercut a bridge, is it acceptable to
>undercut in more than one direction?
>
>Here's what I'm thinking...
>
>Lets say we have a bass bridge that has a footprint of 12"L x 1.5"W (x 2"H).
>If I needed to undercut that bridge, would I be making the footprint
>something like 12" x 7/8" ?  Is that the direction you would undercut?  >And
>the other part was, is it ever a good idea to undercut away from the lower
>end of the bridge so that the footprint would be more like 10.5" x 7/8"
>(still flush to the end on the tenor side)?

* No, and yes. It would be more like 10" or 10.5" x 1.5" There's no need to
make the footprint any narrower. The purpose of undercutting the bass end of
the bridge is just to get the footprint away from the rim a little more to
get some flexibility without adding any unnecessary torque to the
soundboard. Making the footprint narrower would off-center the downbearing
load and torque the board somewhat. That's what you're trying to avoid. 



>I'm trying to get a feel of how far you take this.  Is it of any advantage
>to make the bass bridge in such a fashion as to put it on several "stilts"
>leaving sections underneath open?  That would really let the soundboard
>move?, but then I'd be worried about a good sound energy transfer... I guess
>that's another can of worms, huh?

* Del's probably tried it both ways at some time or other and surely has
more details, but I don't see any real benefit to doing this. At the low
bass frequencies you are dealing with here, energy transfers relatively
slowly and the whole mess goes up and down. There's not much of any
consequence to the bass going on between bridge contact points with that
kind of configuration and you can control flexibility well enough with the
rib design. I'd say keep it simple and glue it down, which brings up another
point. I've always wondered why rebuilders seem to want to glue bridges down
with clamp pressures that exceed the crush point of the panel. I've always
just glued with Titebond and clamped them on with one screw and a soundboard
button between each rib along the length of the bridge, with an auxiliary
clamp at the extreme treble of the long bridge for luck until the glue
dries. No dowels through ribs, or other odd constructions, underneath.
Haven't had one drop off yet. What do you other installers of bridges out
there do?  



>Am I on the right track?
* Hey, I'm still hoping *I* am! While I'm pleased by what I'm hearing on
these projects, there are about a million details I don't really know much
about yet. Just keep asking why and don't take "because" for an answer
without verifying it to your own satisfaction. Start with basic cause and
effect and take it from there. Warning, you are entering the land of
permanent discontent. Welcome.  

>
>Thanks for your input.
>
>Hope you have a great day!
>
>Brian Trout

Yourself,
 Ron