Bracing questions

[deadedith]

There are threads all over the Forum on this, but just to clear my head on top bracing theory:

Is this a perfectly fine method?
1. Assume a 40' top radius is the plan.
2. Radius everything that is to be glued to the top to 40' radius - x-braces, finger braces, tone bars, bridge plate, soundhole braces and anything I've forgotten to mention.
3. Using 3x5 cards or a 40' radius dish, glue the stuff in the right spot.

As to #3 - according to John, Martin glues on a flat surface, then allows the radius of the braces - WHICH braces, by the way? - to pull the top into a dome, along with string pressure.
Is that only for production purposes? Or is it inherently better for some reason than using cards or a dish?

As to #2 - if not all parts are to be radiused, which ones and why?

The steps 1,2,3 make a certain common sense - IF the result sought is a consistent dome - no stress is 'built-in' by squishing a flat plate or finger brace or whatever onto a top in a radius dish.
If a consistent dome is NOT what is sought - why not?

Simple answers please :-)
Thanks

[kencierp]

Yeah -- its a mystery! I have a call in for one of my contacts at the Martin factory Mark Bricket we'll see what he has to say. Rick you are correct we tend to "believe what we want to believe" and egos tend to make it hard for us to accept new facts. With all the minor and extreme variations of the flat top acoustic guitar -- I've come to believe that it is pretty difficult to screw up acoustically if you use the common basic "design formulas" -- then craftsmanship becomes the real issue.

[darren]

Simple answer is radius the bridge, x and tone bars. (how i do it anyway)

I'm on the fence about radiusing the UTB.

And I'm with Rick on building in stress. Seems like something meant to vibrate and reflect sound could even benefit from some built-in tension.

but what do i know?

[Kevin Sjostrand]

You want the top to be flat laterally above the sound hole on the plane that fretboard extension is going to set on. I leave the center 4" or 5" area of those upper braces (tounge depresser and the one with the truss rod access hole" flat, and just contour the outside edges. This seems to work well to keep a flat area for the fretboard to lay on, but still induces some radius out at the edges of the top.
I also do not radius the short tone bars, or the sound hole support braces.
This has worked for me, I think.

Kevin

[Kevin Sjostrand]

Hey Rick,
Thanks for that. I have done this on all 4 of my guitars so I don't have the other scenario to compare it with. I have laid a straight edge across the top at the bridge location, and although I have not measured, there is definately light showing under the rule to either side of the center. Perhaps it is not as pronounced, possibly because of the flat surface (laterally) of the top of the neck block also tends to pull it flat some.
When I brace my next top I will have another look at this.
Thanks again for the insight

Kevin