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As an add on to my x brace question, what height do you folks generally make your UTB's?

I make mine 5/8", but that is in deference to 1930's Martins. Being only 0.325" wide, I think 5/8" would be the minimum.
In 1939, Martin increased with width to 1/2", but the height remained the same.
Stiffness varies with the cube of the height, and proportional to the width. In other words, inceasing the width does not increase stiffness nearly as much as adding to the height.
Another factor is the wood being used. Some of the dense hardwoods like rosewood are nearly twice as stiff as spruce.
Since most of my guitars are tributes to 1930's Martins, I try to pick the densest, stiffest spruce I can find for that brace. IMHO, stiffness in that part of the top is essential to the long-term stability in regards to the neck angle.

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John

That's what I feel too. I was hoping to use my x brace pattern router for the UTB instead of having to make a separate jig. It comes out at 9/16" for the x's which I guess is ok, but I normally go 11/32 by 1/2" for the UTB. Taking 1/16 off the UTB makes me nervous cause of the cube stiffness rule....

Though I've heard of people going 3/8 x 1/2"...

Not that I have seen your jig, but couldn't you just affix a piece of 1/16" veneer with double sided tape to bring the workpiece to the desired width ?

Mine are 3/4" by 3/8". A little extra in this area is better then a little less.
Tom

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A person who has never made a mistake has never made anything!!!

.75 x .50 or so. butted to the neck block. since i don't use a "popsicle", it's an import brace. straight with pillarettes on the ends.

I think that that's the thing to do, Murray...

Tom, I agree...

Arie, what is a pillarette?

From a linguistic point of view, "pillarettes" is decidedly iffy ...almost as iffy as "tentellones" ...

But what they are of course is side reinforcement strips ...and tbh I wholeheartedly concur with arie's view that they should be located directly under the ends of the USB ...it just makes a great deal of sense ...

Aha...