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[QUOTE=Hesh1956]
What I discovered is that when I radius the bottom of a bridge on the 25' radius form that I made in the 25'dish the bridge still will not sit "perfectly" on the guitar top. This means that even though we brace our tops and even radius our bridge plates in the dish the top is not always going to be a 25" radius - exactly. Probably RH plays a part in this too raising or lowering the dome.
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This isn't all that unusual -- at least on classicals. I find that sometimes a top will have "relaxed" a bit, but by insuring that my bridge's underside has the proper arch, when gluing the bridge in place, it will draw the top up into the proper arch.

As several others have mentioned, I also use a bridge gluing caul that I've radiused in my sanding dish. By having the caul and the bridge pressing against the top from both sides, it should push the top into the required arch. Only problem I can see to this might be if there was some RH variances that occured while the top was being fitted to the sides, which might result in some internal stress to the top itself.

I have a question about the bridge plate, though. You guys who build steel strings shape your bridge plates from hardwood -- and I'm assuming that it's well quartered to boot. So, if the plate has been contoured in a sanding dish, shouldn't it still be flat on the reverse side? If so, then it seems to me that you wouldn't need a contoured caul as well. If the reverse side has taken on the contour as well, it seems to me that the plate might have been distorted while sanding it, and chances are it might not be holding the proper arch at rest?

Best,

Michael

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Live to Play, Play to Live

Hesh , Read my above post. Yes the unglued side of the patch is flat, requiring a flat caul, which becomes the bridge glueing caul, and afterwards ,becomes a caul for drilling (clean ) bridge pin holes . To radius the bridge patch ,I have it double taped to this caul and spin the dish on a lazy susan . I'm very careful while radiusing , and spin the dish both ways to avoid any favoritism . Only takes a moment to do , and I check the patch afterwards to make sure the radius is perfect.

Regards Craig

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CRAIG LAWRENCE of AUSTRALIA
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Just to clarify.
The kerfed clamping cauls I show in my last post
I had made years ago when I was doing a lot of
bridge replacements. They flex but still work well
for new builds where the the bottom side of the bridge
plate is flat. I radius the glue side of the bridge plate. If you didnt it would pull the top flat in that area. Old Gibsons and Martins have thin flat bridge plates that curve with the top.

Tom

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http://www.moriciguitar.com