Why are acoustics with straight string pull non-existant?

[zhunter]

Originally Posted by ohYew812

Curious, have you also dedicated your life's work to building world-class, absolutely top-shelf, as-good-as-it-gets, guitars that are also in every aspect of the term "art"?

Mr. K has.

Just sayin'.

Look at that low E on the Collings. If the nut wasn't exerting forces against the string in the plane of the fretboard (say the X axis), the string would work its off the end of the nut. Similarly, the nut is exerting an upward force perpendicular to the plane of the fretboard (say the Y axis) to keep the string in place above the fretboard plane.

Stated more simply looking down the axis of the string, the string exerts a downward force in the Y axis as a function of the break angle in the Y direction and a sideways force in the X axis as a function of the break angle in the X direction. The total force exerted is the vector sum of the X and Y forces and that total force will be greater than either X or Y force by itself. As the break angle approaches 0 in either direction, the force exerted approaches 0 in that direction. So the straight pull result won't have the added force in the X axis.

I must be missing something because the statics solution tells me the extra break angle in the X direction increases the forces the string exerts at the nut.

Assuming the friction at the nut is low enough to allow the tuner to pull the string to tension, it really won't make much difference. When I use a locking nut, the force is sufficient to prevent any movement of the string and it works fine provided the string is tuned, stretched and tuned prior to locking it down. There are other things going on that may render this unimportant like playing style, free length of string behind the nut, etc, but I think the force on the nut is higher on a non straight pull design.

But I wasn't great at statics so please feel free to point out errors.

hunter

[FrankS]

Do a little thought experiment here to see what is going on. Assume the nut is very long (same nut width). There will be a sideways torque on the nut from each string but the NET torque will essentially cancel out because of symmetry of the low E and high E string torque.

What is important though is what does it look like right where the string leaves the nut towards the fretboard. There is only downward force from the height difference from the string on the tuning peg to the saddle (with neck angle included.

Also, look at the way a slot head works.

Frank Sanns

[sabatini]

The next time you hear me playing guitar badly, and I do, think of all the potential practice time I wasted "solving" nonexistent problems on guitar forums.

[zhunter]

Originally Posted by FrankS

Do a little thought experiment here to see what is going on. Assume the nut is very long (same nut width). There will be a sideways torque on the nut from each string but the NET torque will essentially cancel out because of symmetry of the low E and high E string torque.

What is important though is what does it look like right where the string leaves the nut towards the fretboard. There is only downward force from the height difference from the string on the tuning peg to the saddle (with neck angle included.

Also, look at the way a slot head works.

Frank Sanns

I am not sure why the sum of all string forces on the nut is relevant. The point of straight string pull is reducing the forces (and therefore the friction) an individual string places on the nut. There has to be a side force at the nut if there is a break angle in the plane of the fretboard. Draw the free body diagram.

hunter

[ohYew812]

Originally Posted by zhunter

But I wasn't great at statics so please feel free to point out errors.

hunter

I'm not qualified.

However, Mr. Klepper as well as Mr. Sexauer have already explained it in simple terms that even myself, as a layman can understand.

Go back a page and read the expert's 'splain it to you, mang.

[FrankS]

Originally Posted by zhunter

I am not sure why the sum of all string forces on the nut is relevant. The point of straight string pull is reducing the forces (and therefore the friction) an individual string places on the nut. There has to be a side force at the nut if there is a break angle in the plane of the fretboard. Draw the free body diagram.

hunter

The net force means there is no side to side pull on the overall nut.

The reason for looking at the long nut is to show that the forces are not on a single point as a simple vector diagram would show. It would take two vector diagrams to show the forces; one at the tuner end and one at the fretboard end.

At the fretboard end of the nut, the only force is the downward force going down to the saddle. At the tuner end there are two forces, the downward force and the angle to the tuner.

Either way, the combined angles are half or less than the break angle over the saddle so the tangential angle is insignificant in the overall scheme of things for friction and for tone.

Frank Sanns

[zhunter]

Originally Posted by FrankS

The net force means there is no side to side pull on the overall nut.

The reason for looking at the long nut is to show that the forces are not on a single point as a simple vector diagram would show. It would take two vector diagrams to show the forces; one at the tuner end and one at the fretboard end.

At the fretboard end of the nut, the only force is the downward force going down to the saddle. At the tuner end there are two forces, the downward force and the angle to the tuner.

Either way, the combined angles are half or less than the break angle over the saddle so the tangential angle is insignificant in the overall scheme of things for friction and for tone.

Frank Sanns

Like I said it is the individual string that is in play. The overall nut forces don't really enter in. And since the whole thing is sitting still, it is a pretty safe bet the forces in each element will sum to 0. Each element can be broken down into a free body diagram. If help you see that there are X plane forces exerted by the string at the nut then I am out of ideas.

As for the long nut analogy, the load a string places on the nut is much more better approximated and analyzed as a point load. If I could see a benefit to thinking of a moment on the nut about the string axis I would, but at the actual nut width, those moment forces are pretty small. Negligible compared to the X and Y forces. Go back to that Collings (or similar picture). That low E X plane break angle is pretty steep. The G on the other hand does produce a low X plane break angle. However there is one and, therefore, there is a X plane force exerted by the string on the nut.

I play guitars with both designs and really manage to get em all in tune and any affect on tone is completely lost on me. Still, I cannot understand saying no extra force is imposed at the nut by non-straight string pull. Clearly there is.

Whether it matters? Maybe sometimes it does. Maybe sometimes it doesn't Not a big deal either way for me.

hunter

[zhunter]

Originally Posted by ohYew812

I'm not qualified.

However, Mr. Klepper as well as Mr. Sexauer have already explained it in simple terms that even myself, as a layman can understand.

Go back a page and read the expert's 'splain it to you, mang.

Hang around long enough, maybe they'll bring you another fish.

hunter

[El Conquistador]

Originally Posted by Fusion01

Have acoustic luthiers decided this is a non-factor?
I would think those would be better than this example:
Any thoughts?

If, after all the expert opinion offered on this thread, this is still an issue for you, here is a Tony Yamamoto headstock;



Steve

[ohYew812]

Originally Posted by zhunter

Hang around long enough, maybe they'll bring you another fish.

hunter

What's that implying?

[CFW]

Originally Posted by ohYew812

What's that implying?

If I had to guess, it refers to the phrase -

Give a man a fish, and he can feed his family for a day.

Teach him how to fish, and he can feed a village.


And to comment on the idea that there is no lateral pressure on the nut without straight pull, try stringing up only that low E with a nut that isn't glued. I'll bet it shifts around. Try the same experiment with a straight pull. The nut won't move.

Straight pull will only pull then nut downwards. anything else WILL put lateral forces on the nut.

[DanPanther]

I think it becomes a non factor, because the alternative is not acceptable mainstream design.
I would say, any time a string is in straight alignment, it has to be under less stress than if that same string had a deviation in it's alignment. It may not effect tonal quality, but I think it effects structural integrity of the string. Not to a critical point, but at least some.
JMHO.

Dan

[Acousticado]

Originally Posted by SJ VanSandt

John Osthoff here in the US does it. He also compensates the nut, which apparently is easier to pull off with straight string pull. I haven't played one but I would like to. He posts here on AGF - check out his build threads.

Imo, that's one beautiful and intelligent headstock/tuner/nut design.

[mc1]

Originally Posted by zhunter

Look at that low E on the Collings. If the nut wasn't exerting forces against the string in the plane of the fretboard (say the X axis), the string would work its off the end of the nut. Similarly, the nut is exerting an upward force perpendicular to the plane of the fretboard (say the Y axis) to keep the string in place above the fretboard plane.

Stated more simply looking down the axis of the string, the string exerts a downward force in the Y axis as a function of the break angle in the Y direction and a sideways force in the X axis as a function of the break angle in the X direction. The total force exerted is the vector sum of the X and Y forces and that total force will be greater than either X or Y force by itself. As the break angle approaches 0 in either direction, the force exerted approaches 0 in that direction. So the straight pull result won't have the added force in the X axis.

I must be missing something because the statics solution tells me the extra break angle in the X direction increases the forces the string exerts at the nut.

Assuming the friction at the nut is low enough to allow the tuner to pull the string to tension, it really won't make much difference. When I use a locking nut, the force is sufficient to prevent any movement of the string and it works fine provided the string is tuned, stretched and tuned prior to locking it down. There are other things going on that may render this unimportant like playing style, free length of string behind the nut, etc, but I think the force on the nut is higher on a non straight pull design.

But I wasn't great at statics so please feel free to point out errors.

hunter

maybe it would help to mentally replace the nut slot for any given string with a metal ring. the string passes through the ring, and takes a bend there on its way to the tuner post. regardless of straight pull or crooked pull, the string only takes one bend at the loop, and will settle at whatever spot is the shortest distance. it doesn't do a compound bend, regardless of the direction. it's just one bend.

however, with a crooked string pull, that bend is not in the same plane as the fretboard, so it gives the appearance of it being off in two directions.

also, and this is why i wonder if straight pull is better, straight pull is the only pull where the contact point is the lowest part of the ring/nut slot (with the guitar resting on its back), the bottom of the slot.

[Aaron Smith]

The bearing force against the nut is defined by the angle that the string breaks over the nut. The more angled the string is, the more the bearing force is. As Howard described, just because the angle of the string is rotated out of the vertical plane doesn't mean that the angle is any more acute. And if the angle is no more acute, then the bearing force is no greater and neither is the friction.

If the nut slot is cut properly (meaning that it's not pinching the string), then it makes no difference whatsoever whether the string is pushing only against the bottom of the nut slot, or against the side of the slot, or both. For smooth surfaces, friction is proportional only to the bearing force- not to the surface area.

IMO, most of the tuning problems people have are related to poorly cut nut slots, or poor technique in stringing the guitar. When you've made many nuts from scratch, you realize that there is a bit of an art to getting the slots exactly right. And simply changing strings from Light to Medium means that the slots are no longer perfect.