Guitar Engineering 101 Questions

SLBlues

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Sorry for the spam included in the diagram. I did not want to spend the $ to buy the program.

This simplified diagram is supposed to represent the layout of a strat type guitar. My questions are about the relationship of the heights of the string grooves in the the nut versus the height of the saddles in relationship to the surface plate in the diagram. Should they be same height say with the saddle height adjustment screws centered or what? And should the neck be parallel to the surface plate so that the strings are also parallel to the neck? I am assuming the relief recommended for the neck is supposed to account for the oscillation travel of the strings? This diagram assumes the back of the guitar is flat and parallel to top surface of the guitar.
 

David Collins

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You're looking in the wrong direction for reference points. These points are best judged by internal dependency, not external.

The reference best used for your nut slots is the line of the fret peaks directly below the respective string. No need for the saddle positions, neck angle, board radius, or anything like that to be included here. The simplest concept is probably to think of the nut as a zero fret, made level with the rest of them, which just happens to have walls built up on the sides of the strings to keep them in place.

Are you actually trying to adjust, measure, or design something here, or is this just a conceptual question?
 

SLBlues

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It's just conceptual. I have experience building race cars chassis on surface plates so that is where I'm coming from on this. Everything is measured and located using the surface plate as reference. So I was wondering if this could be applied to guitars. Say a strat is set up correctly then where does the nut height end up in relation to the saddle height in the diagram. As I said the diagram is simplified and no frets or pickups are shown and this assumes the nut is already cut correctly for the frets, etc. Will/should the neck (fret board) be parallel to the surface plate and should the strings also be parallel to the surface plate and fret board? This is assuming very minimum relief in the neck. Do these measurements come into play when designing a guitar? It's just something I have been thinking about and thought I would get some thoughts on.
 

David Collins

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I see what you're getting at, but there are just too many other variables on the guitar to make much sense of referencing the nut to the saddle relative to an external plane.

First of course is that necks are often set at an angle to the body. Second is that the range of "correct" setups vary quite widely, meaning for one style of player the saddles would be notably higher or lower than for another. With these changes in saddle height however, the nut height for a proper setup will generally remain independent of that and remain unchanged.

If we're just talking about it in concept here, it would be better to consider adjusting the guitar on the surface plate so that the frets were level with the plate, and the saddles and body considered irrelevant. In this case the bottom of the nut slots will be very close to level with the fret surfaces in the line directly below the respective string (remembering that each will be at a different end height, assuming the fretboard is radiused). In practice, this would be of little use however, as there are simply too many other variables to make measuring in this way practical. From flexibility of the neck, to breakover angle of the string, and a number of other subtle issues, you can achieve much better accuracy and consistency by referencing directly to the frets.
 

Mike Fleming

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This is kind of cool. Yeah i guess I would go with top of frets as parallel to the surface plane, with nut slots in the same plane as the fret tops. This assumes a completely straight neck which will be a slight error since there will always be a tiny bit of relief. Then going with just one string, say the d, it will rise at a slight angle.

Really, to avoid the error, you would have an imaginary reference line parallel to the surface plane, running from the nut to a point just below the saddle tops. The strings would be just above it, intersecting the line at the nut and rising at a slight angle toward the saddles, and then the fret tops would fall away just below it but not in a straight line, maybe a section of a circle or parabolic line (truss rod doesn't reallly affect the neck above the 12th fret).

then you could start calculating, like with a certain scale length, releif of a certain amount will create a certain line of whatever for fret tops, action of x at 12th fret will be angle of y degrees to reference line for string, etc.

I would ignore anything else about the neck except fret tops, and i would ignore the body altogether, since the neck can be at different angles without affecting relief and action.

I haven't thought about things like this in a long time so I hope i don't sound stupid. but this is kind of fun.
 

SLBlues

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Thanks for the comments David and Mike. I think I understand the reasoning for referencing the top of the frets. However, I am having difficultly with the reasoning behind having the neck/plane of the frets at an angle to the body. Why is it or is it desirable to have the strings at an angle to the plane of the frets? The body has to come into play to some degree to be able to have enough adjustment at the saddles to achieve a playable action. The bridge/saddles can't just be positioned anywhere that's convenient to my way of looking at it. I understand set up is as much art as science but there has to be some engineering/science involved in the basic design to allow correct adjustment/set up IMHO. I am still using a strat type guitar as the basis for my rambling. Did Leo/George draw a fret first and add the remainder of the parts? I am not trying to be a smart a$$ just trying to understand this stuff a bit.
 

Mike Fleming

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The nut slot is in the plane of the fret tops (level with the frets) (ideally), so the strings MUST be at an angle to the frest or else they'd be laying on the frets. People often set up a nut to be like 1/100th of an inch higher than the fret tops, so it's virtually level with them.

The reason the string to frets angle is the important angle, vs the string to body angle, is because that is the angle that determines the playability of the instrument. You can have the strings/frets angle the same on guitars with different neck/body angles. It's simply a matter of setting nut height, relief and string height wrt the frets.

the angle of neck to body is only important when you are considering how tall you want your bridge to be. for archtops and etc, you have a lot of neck angle wrt body, becuase the bridge is a big tall thing. for fenders, you have virtually no neck angle, becuase the bridge and saddles are pretty flat. So it's up to you. you can come up with a bridge that works for you first, and then design your neck/body angle accordingly.

Which BTW is what is going on when people shim their fender necks - they need more or less height from their bridges so they adjust the neck/body angle to accomodate the bridge.
 

David Collins

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Though it's understandable to want to frame the arrangement in a reference format you are familiar with, it still may not be the best way of understanding why an artifact is arranged in the way that it is. Pretty much everything functional on a guitar is referenced to the frets, and the body is just there to hold the critical components in their place, give you something to rest on your lap or strap, and a place to rest your arm (though I still think it would be great if they came with cup holders too).

I think it will be less confusing if you think of the fret surface below each string as a straight edge, rather than trying to think of the entire unit referenced against a surface plate. In the most simple and practical sense, think of the design as including a zero fret, with a nut behind it only to set string spacing. And don't worry about relief in basic concept of the design, but imagine the frets as perfectly straight beneath each string. Each line by the way, would be at a different angle to an external reference like a surface plate, as the strings spread out in width over a radiused board. Best to conceptualize it one string at a time, concerning yourself only with the straightedge line of fret peaks below each string as an individual reference for that string.

Everything else regarding body design, neck angle, height of the fretboard above the body, is more an issue of ergonomics, matching hardware dimensions, and practicality of production. All in all, the angle of the body to the neck can be a pretty arbitrary choice.
 

John Coloccia

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Thanks for the comments David and Mike. I think I understand the reasoning for referencing the top of the frets. However, I am having difficultly with the reasoning behind having the neck/plane of the frets at an angle to the body. Why is it or is it desirable to have the strings at an angle to the plane of the frets? The body has to come into play to some degree to be able to have enough adjustment at the saddles to achieve a playable action. The bridge/saddles can't just be positioned anywhere that's convenient to my way of looking at it. I understand set up is as much art as science but there has to be some engineering/science involved in the basic design to allow correct adjustment/set up IMHO. I am still using a strat type guitar as the basis for my rambling. Did Leo/George draw a fret first and add the remainder of the parts? I am not trying to be a smart a$$ just trying to understand this stuff a bit.
Actually, you'd be surprised how much you can do without laying out anything at all. The only thing that's actually important and must be precise are the fret spacing, nut location and bridge location. Nearly everything else can be rough cut, and then fit in place. For example, I can rough cut a body, rough cut a neck (both with enough wiggle room that I know I'm good), and then lay a straight edge over the neck and test fit it to the body to get a good idea of how to size the heel and neck pocket. Mark with a pencil, make a couple of rough cuts, test fit and see how I like it. Is it in proportion, does it look nice? Does it FEEL nice? How's my aim? How much lower do I need to go? Do I want to even go lower, or maybe angle the neck a bit? Trim, fit, trim, fit.

Eventually, your prototype will be done, you'll look at it and say, "Hmmmm....next time I want to move this over a bit, do this, do that etc". You take it apart and take your measurements, incorporating your changes, maybe make some fixtures or another protoype, and there you go. A couple of times doing this you have the finished product.

There is a great deal of craftsmanship that goes into a guitar, but you really don't need to over think the basic design. I find it much easier to shape my ideas with wood in hand than trying to draw everything and lay everything out perfectly the first time. Just build it. Leave everything a little big. Nice straight and parallel surfaces. You can shape them later. It's much easier to take off 1/16" if the opposite side is flat and parallel. Just basic woodworking. If you screw up, glue it back together or just use another piece of wood. Use cheap wood for prototypes. If you're just trying to get basic shapes, use pine if you want to.

Remember that even the Mona Lisa started out as a few simple sketched lines on a canvas. You don't start by laying out every drop of paint. You start with basic rough shapes and refine from there.
 

walterw

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right, the "critical" dimensions are the fret tops, nut slots, and saddle contact points.

everything else is just design choices, based on tone, mechanical functionality, tradition, comfort, style, whimsy, perversity, whatever.

hell, sometimes the rest can be left off entirely.
 

Mike Fleming

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Like Joe is saying -- I would say george and leo built a guitar with no neck/body angle because parallel planes are easier than angles from a manufacturing standpoint - you just plane boards and route cavities. Then you design the neck to sit up high enough above the top of the body to give you clearance for a low profile bridge.

Notice too that when G&L used that horseshoe bridge that's taller than a fender bridge, they didn't introduce neck angle to accomodate the extra height, they made the neck sit higher off the top of the body, but still parallel.

EDIT: Forgot to add -- that picture is wild walter!!
 
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David Collins

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I love that picture Walter - Great demonstration of the concept, but my favorite part is that amongst all the techo-simplicity and streamlined design, the hexaphonic pickup departs in six separate RCA cords dangling from the tail. :)

That was the 70's, wasn't it.... :)
 




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