How To Determine A Neck Angle

[rhoads56]

I want to ask one question to this topic if I may.

In step 4 of Perry's drawing, the body angle is drawn in relation to the height of the bridge, but the picture shows a body meeting the neck at the end of the fretboard.

If the guitar design has the body meeting the neck at say 16th fret, you would draw your body angle line, from the 16th fret(at glue side of fretboard) to the base of the bridge point, or does that matter and follow the diagram as posted?

Also if someone could repost the neck/string taper image again it would be an appreciated visual reference to base my drawing against.

Yes, you can start the body anywhere you like. You could also start it at the 16th, and drop it lets say, 3mm, also. The point that the body starts isnt relevant. It's where ever you want it to be. All it does is visualize, and calculate, the angle you need

[Prostheta]

I'm not sure if I understand what you are asking 100%.

The body angle is derived from a combination of the height that the bridge requires and also the fretboard height above the body plane. Take for example a 70s Gibson Flying V where the fretboard was a huge height off the body which reduced the requirement for a large neck angle. Modern Flying Vs have a lower fretboard/board height which increases the angle.

If you want to do it as mathematics, try this example:

n1 - saddle witness points need to be at least 10mm off the body

n2 - fretboard (including fret height) is 7mm off the body where they meet

n3 - saddle witness line is 160mm back from the body/fretboard meeting point

Subtract the n2 from n1 (10-7=3). Use a little bit of trigonometry since you know the opposite (n1-n2) and adjacent (n3) but need to know the angle. Using tanθ = opp/adj = (n1-n2)/n3 = (3/160) gives us an answer of 1,07°.

This is by no means a perfect method since it does not take into account string action, fingerboard radius, etc. It does illustrate how you can derive an approximate angle to work from in which case you can easily draw it out to confirm whether it is satisfactory. Also you are able to work this backwards to figure out what plugging in specific neck angle values or neck-body height offsets will do for you.

I hope this helps.

[Prostheta]

I sort of used this idea (minus the maths) in planning out a neck:

http://projectguitar.ibforums.com/topic/47509-project-80s-aria-pro-ii-rsb-retrofit-black-n-gold-neck/?p=530223

[Bjorn.LaSanche]

I want to ask one question to this topic if I may.

In step 4 of Perry's drawing, the body angle is drawn in relation to the height of the bridge, but the picture shows a body meeting the neck at the end of the fretboard.

If the guitar design has the body meeting the neck at say 16th fret, you would draw your body angle line, from the 16th fret(at glue side of fretboard) to the base of the bridge point, or does that matter and follow the diagram as posted?

Also if someone could repost the neck/string taper image again it would be an appreciated visual reference to base my drawing against.

Yes, you can start the body anywhere you like. You could also start it at the 16th, and drop it lets say, 3mm, also. The point that the body starts isnt relevant. It's where ever you want it to be. All it does is visualize, and calculate, the angle you need

I am following you. I just was wondering if the actual neck drop angle would change slightly if the top of the body intersected with top of the neck at a different position than the one you drew up? I guess it would in relation to where I put it in my design(neck meeting body at 16th fret) compared to a guitar where the body joined the neck at the end of the fretboard as in a LP Special DC(neck meeting body at 21st fret).

If I join the body further into the neck, the angle of neck drop will be a little less than what you drew, but the key elements that determine the angle are the string action off the fretboard, height of the radiused fretboard, and height of the bridge at scale length to the body.

I'm going to have to draw this up on paper to verify for myself.

@Prostheta, I will take a look at the trig, but Perry's mock up is very simple and easily understandable. I think at this point the math will confuse me. Once I get a handle on the other way, the math will solidify my understanding.

Thanks guys for your help.

[rhoads56]

Yes, the body angle will change. More importantly though, the height of the bridge wont.

Forget the math. Ive never, ever, EVER, needed to, or even KNOWN the actual angle of any body to neck join, for any guitar Ive built. It's irrelevant. It is just a number. Even if you knew that angle, transferring it to a body blank is excessively awkward. But, if you've drawn it like I do, it's really easy.

[Prostheta]

Depends how you build. Mine are always done with jigs and fixtures which rely on specific underlying calculations. You're right, but the approach to the problem depends on the designer's style and both approaches are relevant.

[rhoads56]

Sure, but if the body joins at the fretboard glue line, and the imaginary fretboard glue line is 12mm above the body AT THE BRIDGE, and that point is, lets say, 250mm from the body joint at the neck, then you need to pack your jig 12mm high for every 250mm in length. If the jig is lets say, 600mm long, then it needs a 28.8mm packer to be at the correct angle (12/250x600=28.8).

If the body is 5mm below the glue line, the bridge is still 12mm, so its 7mm over 250 (using a 600mm jig = 7/250x600 = 16.8mm packer)

I cant see an easier way of doing it than that.

Finding the actual correct number of degrees, then has to be calculated back to a number to find the packer size. Double handling!

When I run my courses, the guys draw it out, see it, and implement it in a matter of minutes. I havent had a fool come through the course yet, so I cant say it's fool proof, but I'd be willing to bet...

[Prostheta]

It's about the same thing, except you are working in gradient as opposed to angles. You're right in that an angle is an irrelevant type of value, especially for your methods of working when you work from value-to-target. I guess that this exposes a significant difference in design methods since I work purely in CAD and you work "from the wood upwards" if you see what I mean. Perhaps my motivations for working the way I do come from from a manufacturing perspective (quantification, repeatability, etc.) whereas yours are more pragmatic, coming from the pure custom side of things. Both are equally relevant and have given me good food for thought for when I get to writing articles on instrument design. I should definitely consider broaching both thought processes.

As for the guys on your course, I am sure they are more of the type who are building single instruments from that same custom process as your own as opposed to delivering production-ready processes, thereby making your "bet" a foregone conclusion? Those are the only bets I ever like to make too. ;-)

Yeah, I agree that expressing neck geometry in terms of its angle can appear somewhat redundant given that there are other factors which make it less relevant.

Good subject for discussion Perry.