Top radius and neck angle relationship

[kinspeed]

Can someone explain this to me? Where is the pinnacle of the top radius in relation to the bridge? Should it be right at the bridge or before it, closer to the soundhole? Thank you!

[johnnparchem]

For the top, if you use a radius dish you get an arc from the heel to the end block. The pinnacle is in the center of the top. The back is sloped but relative to the plane of the slope there still is an arc from the heel to the end block. Find John Hall's video on Utube and watch the way he uses a radius dish for the neck angle. It is very complicated to get the neck angle right, the first time you really need to follow one complete process start to finish. THere are a lot of ways to set a neck angle that work, but if you mix methods they rarely work.

[MaineGeezer]

It's complicated, and there seems to be several ways of dealing with it. Carter Ruff, the luthier who is giving me "lessons" in guitar building, builds his guitars with a radius over the entire top. This produces a wedge-shaped gap between the fingerboard extension and the top, because the top curves downward. It gets filled in with a thin wedge of wood.
Some people think that way of doing it is totally bogus and misguided. Their approach (I think) is to not radius the front section of the guitar top. it's flat and perpendicular to front of the head block, so the fingerboard extension sits down flat on the top with no gap.

Either way works, if you do it correctly. I'm not sure which might be easier to do, as for the three guitars I've made I've always done it Carter's way with fully radiused top that requires a wedge filler.

Here's a drawing that may -- or may not -- clarify what I'm talking about.

[tippie53]

there are a differing schools of thought on this. I don't radius the entire top as for my ear the full radius does dive you a different sound but that may be what you like. I had made a few with full radius tops and didn't like them.
My method is similar to many
https://www.youtube.com/watch?v=pz6xzVRA51E&t=43s
note that here I am only going to radius the top from the top of the soundhole to the neck block. I use a 28 foot dish and this creates a consistent neck angle for me. One thing you is that more you radius the top the higher the neck angle and the more the top is going to get torques. There is a point where the tone makes a change.
If your using a Martin kit you don't want to do it that way. I know people that are great builders and they use lower radii on the tops when they dome the entire top. Usually 40 foot or more.

Find your technique that suits your ear. hope you found the different info here helpful

[kinspeed]

I think I have more questions now. With the center of the guitar being the pinnacle of the dome, where should my neck block be in relation to my heel block? Lets say I use a 28' radius will the neck block and heel block be equal height from my mold or is the neck block lower than the heel block? It looks like it is in Johns video.

[johnnparchem]

I can not answer those questions as I do not think in any of those terms while building. What I want is the upper bout to be in plane with the neck. I want a straight edge running along the neck and the upper bout without the fretboard to project 2.5 mm above the top at the saddle location. All the geometry is to make that work. I personally use a 28' or a 32' radius dish on the entire top. I take the heel and end block down evenly on the top. At the point that the entire top is radiused the sand paper touches everywhere, I find I have a bit too much angle on the heel block so I reduce the angle of the upper bout with a flat sanding disk. The flat sanding disk also flattens the lateral curve on the heel so the fret board lays flat I will clamp an unbraced top to the rims lay a straightedge on the upper bout projecting over the saddle location and check the height of the straight edge at the saddle location. If it is not 2.5 mm I adjust the rims.

It might be worthwhile to get a large sheet a paper and draw out a side view of the guitar, that includes neck angle and any radius you put on the top. If it is a steel string your goal is to be able to run a straight line from the nut or first fret 2.5 mm above the 12 fret and then 13-14 mm above the top at the saddle location. From that drawing you can see what neck angle you need. You want the angle on the heel block to compliment the neck angle.

It is important to note that there are bunches of different ways to do this, and all of them could be made to work, but make sure you follow only one way.

[MaineGeezer]

When I set up the sides and end blocks in the mold, I have the top edges of the sides straight. The bottom edges have a profile, but the top edges are straight. I glue the end blocks flush and perpendicular to the top edges of the sides. The bottom of the end blocks matches the profile of the bottom edges or extends a bit beyond. In any case, what you want is for the end blocks to sand to the same radii, top and bottom, as the sides.The front block is going to be shorter than the tail block because the body depth has a taper from end to end.

I get the impression that some people manage to cut the dovetail so that when it's assembled the neck position is correct with no further work. I can't do that. When I first assemble a neck joint, the alignment is almost certainly way off. If it ever lined up correctly, I would be amazed. I adjust the neck angles as necessary by sanding the faces of the heel that contact the body, or I may add some thin shims in the joint.

[tippie53]

your missing the point here Kinspeed on a few points. On the Martin style that is the one I use
there is no pinnacle . On the top there will be 3 areas A the angle from the neck block to the top of the sound hole . When you drive the bus you create 2 partial domes one at the neck block another at the tail block. The neck area then gets trued with the flat side of the dish to create a flat angle plane , then a flat area between the hole this is created when you true the sides in the mold. then there is just a slight dome that is from the 28 dish.
you are trying to control the geometry on the top for the fret plane and string line to meet the saddle at a precise point so you have have the best action height and string height off the top.

You may be over thinking this a bit.
If your using an entire dome then you have to be precise on how you dome it. I have tried the full domes and always had issues.

Maine Points out about some people use a fixture to cut the dovetail after the body is built. These are a great tool as it make setting the neck pretty easy. You best bet would be to take the time to draw this out.
What I don't like about full domes is it easy to get the top over torqued and this makes the top sound tight. John Parchem can speak more on his methodology as he has done this and he has a process that works for him.

Once you draw it out you can see how this works
there are a few variables you have to consider , how much the top will rise on string load is one of them. On my style you can expect about 3/32 rise.

[kinspeed]

you are trying to control the geometry on the top for the fret plane and string line to meet the saddle at a precise point so you have have the best action height and string height off the top.

You may be over thinking this a bit.

I'm sorry to disagree with you here John, but I don't think I'm overthinking this considering that it needs to be at a "precise point". The top radius dictates the play-ability of the guitar. I believe that optimizing the top radius can make or break your build. Screw it up bad enough and you might as well start over.

I had the opportunity to examine an amateur build recently and the neck set and top radius were so screwed up that he built it with the fretboard about a 1/4" off of the soundboard. That's not my style. I study things out and build them over and over a thousand times in my head before I actually do it. I'm stuck with that kind of sickness, sorry! lol

[Ben-Had]

you are trying to control the geometry on the top for the fret plane and string line to meet the saddle at a precise point so you have have the best action height and string height off the top.

You may be over thinking this a bit.

I'm sorry to disagree with you here John, but I don't think I'm overthinking this considering that it needs to be at a "precise point". The top radius dictates the play-ability of the guitar. I believe that optimizing the top radius can make or break your build. Screw it up bad enough and you might as well start over.

I had the opportunity to examine an amateur build recently and the neck set and top radius were so screwed up that he built it with the fretboard about a 1/4" of of the soundboard. That's not my style. I study things out and build them over and over a thousand times in my head before I actually do it. I'm stuck with that kind of sickness, sorry! lol

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