Help finding the angle of a guitar body relative to the neck

[Jaan]

Hello there. I'm trying to recreate a guitar body left handed (it's a right handed guitar). The body of the guitar is angled in relationship to the neck very much like a Gibson. Since there are few truly flat surfaces I'm trying to find the overall angle of the body of the guitar in relation to the neck using the dimensions of the pickup mounting ring. I've made a drawing of the exact dimensions. Thank you in advance for your help!

 

[Dr.Peterson]

Hello there. I'm trying to recreate a guitar body left handed (it's a right handed guitar). The body of the guitar is angled in relationship to the neck very much like a Gibson. Since there are few truly flat surfaces I'm trying to find the overall angle of the body of the guitar in relation to the neck using the dimensions of the pickup mounting ring. I've made a drawing of the exact dimensions. Thank you in advance for your help!
View attachment 10235

If you know some trigonometry, draw a horizontal line to turn the slanted line into the hypotenuse of a right triangle (assuming the top two angles are right). You can easily find the lengths of both legs, and then use the inverse tangent to find the angle.

For clarity, though, which angle do you want to know?

 

[Jaan]

If you know some trigonometry, draw a horizontal line to turn the slanted line into the hypotenuse of a right triangle (assuming the top two angles are right). You can easily find the lengths of both legs, and then use the inverse tangent to find the angle.

For clarity, though, which angle do you want to know?

This angle right here should give me the angle between the neck and the body. I need that angle to correctly cut out the neck pocket.

 

[Jaan]

If you know some trigonometry, draw a horizontal line to turn the slanted line into the hypotenuse of a right triangle (assuming the top two angles are right). You can easily find the lengths of both legs, and then use the inverse tangent to find the angle.

For clarity, though, which angle do you want to know?

You're correct that the top two angles are right angles. The angle circled should give me the angle I need to correctly cut out the neck pocket (it's a bolt on neck). Sorry it's been 30 years since I did any of this stuff.

 

[sinx]

Hello there. I'm trying to recreate a guitar body left handed (it's a right handed guitar). The body of the guitar is angled in relationship to the neck very much like a Gibson. Since there are few truly flat surfaces I'm trying to find the overall angle of the body of the guitar in relation to the neck using the dimensions of the pickup mounting ring. I've made a drawing of the exact dimensions. Thank you in advance for your help!
View attachment 10235

is one of the angles 90⁰​?

 

[Jaan]

For clarity, though, which angle do you want to know?

The two angles along the top are 90 degree angles. The angle I'm trying to find is this one;

 

[Dr.Peterson]

The two angles along the top are 90 degree angles. The angle I'm trying to find is this one;
View attachment 10247

The triangle I described has legs 1.785 and 0.095. The ratio of these, which is the tangent of the angle you want, is 1.785/0.095 = 18.789, and the inverse tangent of this is 86.95 degrees.

 

[sinx]

This angle right here should give me the angle between the neck and the body. I need that angle to correctly cut out the neck pocket.
View attachment 10237

I suggest you talk to a luthier who is experienced with neck resets.
He could give you the angle you need.
[Unless this is a really old guitar, the angle you need should be pretty much standard, as fingerboards are mass produced (and are the same), so stop lengths (and neck angles) are the same.]

the angle on the pickup may be right for the guitar neck, but I would not trust it. A slight error on the neck/mortise joint makes a lot of difference.

For a violin anyway, and probably guitar, the way to do this is; the mortise in the neck block is cut flat and true with the rib assembly (of the corpus, or body of the guitar/violin).
Then all of the neck angle is cut on the heel (of the neck).
and you fine tune the neck set via the cut on the heel.
[the heel is much easier to work with than the mortise.]

for the geometry problem you presented, Dr. Peterson gave the solution.

 

[Denis]

The two angles along the top are 90 degree angles. The angle I'm trying to find is this one;
View attachment 10247

Problem is quite simple:
a = .456 - .361, b = 1.785
You now have the 2 legs of a right triangle.

Solving for the angle is also easy; 3 ways: pick your poison here:
https://www.mathsisfun.com/algebra/trig-finding-angle-right-triangle.html

 

[Jaan]

Thank you everyone! It's all coming back to me now. I've made several guitars in the past, I just needed a good starting point for when I mount it into my milling machine. If the worst comes to the worst, it wouldn't be the first guitar that's ever had the neck shimmed. (c: I'll post pictures when I'm done!