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I've been building with a 25' radius on the top and a 15' radius on the back. I still haven't gotten to a replicable, dependable process for neck angle, without getting it all set up, then readjusting (with bolt on neck, not a catastrophe, but certainly not ideal). I suspect part of the issue is the radius under the fretboard extensionis the issue - and sanding it flat is OK, but I'd like to consider another option.

Does anyone glue their UTB on the top flat (e.g. without a radius) perhaps as a second step of gluing bracing, after the x brace and finger braces are shaped (with the radius) and glued on the radius dish?

My hypothesis is that the upper portion of the top would be flat, enabling the fretboard to be glued flat without the need to sand it flat, and the rest of the top radiused.

Interested in your reactions, and what I may be missing on this (one challenge I see is that I wouldn't be able to use the radius dish to sand the kerfing flush......

Setting up your guitar for the neck geometry is key. Too much radius on the top can do things tonally also . Here is a video link to help you understand what we need to do. The key is matching the neck geometry to the side. In most cases we are using a 1 1/2 degree neck angle. I want to see a final action height of 3 and 2 64s on the 12th fret and string height of 1/2 inch at the bridge . To do this I use a 1 1/2 degree initial set up. I actually incorporate this into the sides themselves. This helps to control that 14 fret hump. I don't radius the entire top just the area of the extension and what follows behind the bridge. I use 28ft on the top and 15 on the backs. 25 will tend to throw the neck angle steeper and make hitting that 1/2 inch target a bit trickier. Also the top will be flattened in the fretboard area. utb is flat in my builds.
http://www.youtube.com/watch?v=QYHPCeVRUA4
This link will go into more detail than I can here. I hope this information helps.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I agree with John, 25' top radius makes neck set problematic, the board end wants to fly too high.
After doing a flat top and finding a nice tone, and nicer neck set, I'm going to do my next at 35' top radius.

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https://www.facebook.com/profile.php?id=100008907949110

I don't recall seeing any radius to the top of any of my guitars. I've had a couple of Martins, a Gibson J50 and a Guild D25. Is it just hard to notice?

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Hutch

Get the heck off the couch and go build a guitar!!!!

I use a 10' radius on the back and a 15' cylindrical on the top. The center is essentially flat from neck block to the end block. Works perfectly.

Altough I use slightly less arch on the UTB than on my X braces I think you're looking on the less important part of the issue. And a flat UTB could actually make things worse.

What I mean is that the arch on the top that goes accross the width of the fingerboard is not that important, it's a very small distance with a fairly small arch- you can sand that flat. The real problem is the neck angle. For that you need the top where it touches the end of the fingerboard to be higher than at the 14th (or 12th ) fret. The arch or no arch of the UTB needs to be taken into consideration with the side geometry to give the top under the fingerboard the right slope. The slope of the top heel to tail is the key.

John