www.KitGuitarsForum.com

Bridge plate question: if the top is now radius by the braces, why isn't the bridge plate radiused? Similar question for down the road when I glue the bridge plate down. Nothing in the instructions says radius either of them, but they are being attached to a top that will have slight radius.

I do sand bridge plates to the top radius in the appropriate radius dish. (Same for the underside of the bridge, but that curvature is the other direction so you first have to make an appropriate sanding block by sanding a block to shape in the radius dish.)

I always sand the radius on the bridge plate and the bridge. I made a simple sanding block, by sanding it on the dish. This gives me the opposite curve needed to sand the underside of the bridge.

I used judicious sanding in the beginning, sanding little then laying the bridge on the top. I did this until it laid down on all sides. Same for the plate. Now, I have a block that I use for that purpose.

BTW, that was a very good question, and IMO a good catch.

I did this a few times and found there were issues down the line. Martin never radiused a plate or bridge and they build more guitars than anyone.
Can you yes so make it your own call
here is what I can tell you.

RH will change and this can cause stresses . My issues were cracks in the top formed and the edge of the bridge. Since the plate and bridge work together and also with RH stress the corners won't cause a stress risor.

NEVER RADIUS ON A MARTIN.

I learn something new daily. Thank you John.

Hmmm....interesting. I'm going to have to think about how that would work with humidity changes.

So if one keeps the bridge and plate flat, when they are glued they locally flatten out the top. The stress caused by flattening the top must be insignificant I guess I can go along with that, though it seems it might increase the tendency of the ends of the bridge to lift over time. I don't have enough experience to know one way or the other.

It's not clear to me though, why sanding the bridge and plate to the top radius can create conditions that lead to cracks, when forcing the top to be flat, doesn't. I don't understand what happens in that case, vs flattening it out.

I'd think it would be more important to be sure the edges of the bridge plate are not parallel to the top grain. (If the edges of the bridge can be angled relative to the grain as well, even better.)

Anyway, I am confused about this detail of construction.....

ebony is a hard wood and in many designs the plate is short of the ends of the bridge and right off the X braces
As the wood dries out , it becomes stressed in tension across the grain. With the ends of the bridge radiused down and at a point right off the X brace that is supporting the top and only the wings of the bridge , the top then starts to sink and the curve opposite the radius you would have put in it stresses the top and POP .
I did this on 2 guitars following advice I had heard on the web. They both cracked and I figured Martin never did it Gibson did it flat and Tayor didn't radius so maybe one of those infamous inter web falicies.

John,
Just so I am clear, you DON'T radius the bridge PLATE, but you DO radius the BRIDGE?

I don't radius the bridge plate, but I do radius the bridge to fit the top radius. So far, with the oldest guitar I've built going on 9 years, none have lifted, etc. Even two guitars in India for a number of years with high humidity....no issues.

I DO NOT RADIUS BRIDGE OR PLATE!
Martin
Gibson
Taylor
Wayne Henderson
none radius a bridge