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Ok, so you just do that by eye with a block plane do you? Or is there some other jig or dish you need to do it?

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"I am always doing that which I cannot do, in order that I may learn how to do it."
Pablo Picasso

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Hey Todd - With your radius system how much space do you get at the saddle area when you put a straight edge above the sound hole and run it down the center line (does that make sense!?)? Do you sand down the sides any at the heel block area, to achieve correct neck angle?

I have had success (though I haven't made many instruments) with using a flat UTB and getting the neck angle the way I want. The thought of using a slight arc (closer to flat than the normal top radius) to build in a little insurance from humidity changes appeals to me. I may as well use the 60 ft (or close enough) that you all are having success with. How much offset over say 24" would it take to approximate a 60 ft. radius. I'd like to just make a template of that arc and draw it on my stock, plane to the line and call it close enough.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Very handy tool for calculating arch offsets http://liutaiomottola.com/formulae/sag.htm

Handy indeed, thanks Dennis! I come up with 0.1 inches over a 24 inch span.

Oops looks like Todd sent me a fish while I was shopping for bait and tackle. . .

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Bryan, I just take a couple of swipes on each end of the UTB with a block plane. Works for me.

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Steve Smith
"Music is what feelings sound like"

Yeah Steve, I knew the offset wouldn't be much but once I did the numbers It became obvious just how small the offset would be over the length of the typical UTB. I'll probably not bother with a template and just take of a few wisps as you described.

And I didn't properly thank Todd. Sagitta was the term I couldn't come up with when I tried to find a calculator on the internet.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

I do it like Steve does. 1/16" off the ends with a block plane from a 2 1/2" flat center. Then I just slightly sand the heel block on a sanding board with a thin wedge propping up the tail block. Get's me .090" at the saddle.

I do like Dennis K..go about 28' (top radius) but leave a flat spot in the middle for the fingerboard extension, smoothed out to create some even-ish transition. I glue it on to the top in the dish.

Also, I glue my tops onto a flat rim...that is, I have not sanded the top rim in a radius dish. I do bevel the tops of the kerfed lining, to about 1.5 degrees, to accommodate the dome of the top. It all glues down and is nice and smooth.
Nothing revolutionary...Martins (and many clones, including mine) are build like this since...forever?

I radius everything to 30'. Then I plane a small flat in the middle of the UTB. I glue it in the dish with a few pieces of binding tape on the top where the flat is.

Later, I use one of those sanding paddle jigs ( that I copied from somebody here) that pivots from the bridge area to make sure its good and flat. The end of my fretboard usually ends up rising about .020-.030 which seems like a good amount for a little fall away.

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Pat

I've gone to all flat on all braces on my last several builds and think I will continue down that road but I used to arch the UTB. I use an A-Brace pattern to strengthen that area. I'm not sure I understand this method using a 60' radius. Are you saying you have a radius but you glue it by forcing it flat with clamps rather than either using a flexible back slat or a radius dish when adding clamping pressure? If so.. Why?

Ok, I'm still trying to think this through. So when you force fit the 60' radiused brace to a flat top does it spring back to the arch? So IOW if you run a straight edge along the length of the UT brace on the guitar top (after glued up) will you see that the top is radiused to the brace at 60'?

If so this is why I am confused. Why would you not just glue the brace to the top using a slat as a caul so that the top conforms to the 60' radius without the stress of force fitting. IS there a reason to put this brace under stress for structural purposes?

Or am I just not getting it? Quite possible I am not.

The 60' radius arches the top about 0.030" on each end of the UTB - no stress to speak off. I do all the other braces in the radius dish as usual then just clamp the UTB on with some cam clamps as the last step. The UTB is very stiff so the top just conforms to the arch.

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Steve Smith
"Music is what feelings sound like"

Ok I see, thanks.

How do you all sand the rib assembly before attaching the top? Sand it to the dome radius or just leave it flat? The martin factory tour video shows flat sanding and then sanding a 1.5 degree angle from the waist to the neck block.

If you sand the whole rib assembly with the radius of the dome then you get an angle on the neck block and it won't flushly fit the underside of the top?