Why are acoustics with straight string pull non-existant?

[RustyZombie]

Originally Posted by 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.

Alan Carruth has said that the break angle (over the saddle) has nothing to do with the bearing force, once you achieve enough of an angle to keep the string from skipping. I'm by no means as knowledgeable as Mr. Carruth, but I don't see why it would be any different with the nut.

[sshan25]

We all know how much everyone here loves Seagull headstocks. Need l say more?

[Ned Milburn]

Unless the break angle over the nut is at an extreme angle, nut slots can be cut carefully with a gentle curve which splits the difference between the headstock and fretboard string angles, and this should avoid any binding troubles experienced in this area. The "101" entry level nut slot cutting technique is to cut them straight. Cutting with gentle angles (vertical AND horizontal) avoids the string making two sharp "bends" or "turns" as it enters and exits the nut slot.

[Fusion01]

Originally Posted by CFW

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.

Thank you. I was going to post this example as well. I recall an example of a left handed bass I bought for cheap and I had to turn the nut 180 degrees (so I could use it right handed) and instead of gluing it I just figured string tension would keep it stable. But as you stated, the string break angle at the low E significantly pulled the nut about 1/4" out of the nut slot toward the bass side (which in this case is reversed since the headstock is upside down from normal, since it was a left handed instrument strung right handed). This to me proves there are lateral forces at work besides only downward forces at the nut. If there are no lateral forces, that nut would have never moved.

[Aaron Smith]

Originally Posted by RustyZombie

Alan Carruth has said that the break angle (over the saddle) has nothing to do with the bearing force, once you achieve enough of an angle to keep the string from skipping. I'm by no means as knowledgeable as Mr. Carruth, but I don't see why it would be any different with the nut.

I'll let Alan speak for his own work, but I've read most of his posts here and I don't think that's what he said.

His study was looking at break angle over the saddle; he concluded that once you have enough of an angle to create enough bearing force to keep the string from slipping across the crown, there is no additional tonal advantage to having more. However, the break angle does indeed create more bearing force (and thus more friction) as it becomes more acute; it's simple physics.

[mc1]

Originally Posted by CFW

...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.

Originally Posted by Fusion01

Thank you. I was going to post this example as well. I recall an example of a left handed bass I bought for cheap and I had to turn the nut 180 degrees (so I could use it right handed) and instead of gluing it I just figured string tension would keep it stable. But as you stated, the string break angle at the low E significantly pulled the nut about 1/4" out of the nut slot toward the bass side (which in this case is reversed since the headstock is upside down from normal, since it was a left handed instrument strung right handed). This to me proves there are lateral forces at work besides only downward forces at the nut. If there are no lateral forces, that nut would have never moved.

but it's still only bending in one direction. the lateral forces are simply in relation to an arbitrary reference (90 degrees to the nut).

for me it really helps to conceptualize the nut slot as a ring, or loop, or doughnut. no matter which way the string passing through it bends, it is always, and only, in one direction.

what wonder is if it is easier to slot the nut for straight string pull.

[zabdart]

The old Ovations used to have straight string pull over the nut.

[John Osthoff]

Originally Posted by Acousticado

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

Thanks Tom,

I worked on headstock design this for a long time. The straight string pull just makes sense to me. It took me more than a year to commit to the design. I was working on this before Gore came out with his books, but I will give him credit for the some process I used on the nut compensation.

Leaving a more traditional headstock for this new design was sort of an agonizing decision as many potential buyers and clients are sort of locked into the more traditional look. One thing that can't really be seen in the photo is the stealth trussrod cover, but that is getting a little off topic, so I won't go into details in this thread. I had one client (who's opinion I value) tell me he didn't like headstock after I made the transition to the new design. A year later, he told me it was growing on him, and over time he began to like it. This design is a big departure from tradition.

The nice thing about being a custom builder is I have the flexibility to change things up a bit as needed. I recently completed a guitar with a slothead, and I have custom order that will get a more traditional headstock (on the slope shouldered dread.) I (mostly) prefer build guitars with my SSP (straight string pull) headstock, but as mentioned it is nice to be able to change things when a design seems to warrant it.

[Acousticado]

Originally Posted by John Osthoff

Thanks Tom,

I worked on headstock design this for a long time. The straight string pull just makes sense to me. It took me more than a year to commit to the design. I was working on this before Gore came out with his books, but I will give him credit for the some process I used on the nut compensation.

Leaving a more traditional headstock for this new design was sort of an agonizing decision as many potential buyers and clients are sort of locked into the more traditional look. One thing that can't really be seen in the photo is the stealth trussrod cover, but that is getting a little off topic, so I won't go into details in this thread. I had one client (who's opinion I value) tell me he didn't like headstock after I made the transition to the new design. A year later, he told me it was growing on him, and over time he began to like it. This design is a big departure from tradition.

The nice thing about being a custom builder is I have the flexibility to change things up a bit as needed. I recently completed a guitar with a slothead, and I have custom order that will get a more traditional headstock (on the slope shouldered dread.) I (mostly) prefer build guitars with my SSP (straight string pull) headstock, but as mentioned it is nice to be able to change things when a design seems to warrant it.

John, I have to say that this overall design of yours appeals to me like no other.

[FrankS]

John, Really nice headstock. Congrats on one of the nicest I have seen!


As stated in one of my previous posts, the pulls are more for looks than for dramatic tonal differences. if you want to try an experiment, wind your low E and high E strings in the opposite direction. This will move the strings outward the width of the tuning peg and into a more parallel line.

I doubt anybody would want to do this permanently as tuning will be in the opposite direction with this reversal but it is an easy enough experiment to undo. Not many things with guitars are this easy to test.

Frank Sanns

[nedray]

This headstock is similar to the Osthoff shape, although slightly less straight on the inside strings. It is the smoothest tuning and best at staying in tune of any guitar I've owned. That's partly due to the tuning machines too, which are smoothest turning of any I've experienced. In general, PRS made a big effort to emulate a variety of best practices when designing these, and a straighter string pull seems to be a product of that process.

I bow to the master builders here on the physics of the thing, and I have to say my Martin, Collings and Santa Cruz acoustics have never caused me serious tuning problems attributable to nut slot friction. On the other hand, Gibson electrics, especially Les Pauls, are notorious for tuning instability due to string binding at the nut--especially the inside strings. Similarly, a Bigsby-equipped Gretsch is practically unplayable until you lubricate the nut slots. Are those nut slots simply cut too tight? I've always thought the bend angle at the nut caused the problem, but it seems only to apply to electric guitars.

[RustyZombie]

Originally Posted by Aaron Smith

I'll let Alan speak for his own work, but I've read most of his posts here and I don't think that's what he said.

His study was looking at break angle over the saddle; he concluded that once you have enough of an angle to create enough bearing force to keep the string from slipping across the crown, there is no additional tonal advantage to having more. However, the break angle does indeed create more bearing force (and thus more friction) as it becomes more acute; it's simple physics.

I'm not sure how you cannot have a tonal change if there is a change in the bearing force. But if I read too far into what what Mr. Carruth was saying, then I certainly won't mind if he corrects me.

[Long Jon]

Originally Posted by nedray

This headstock is similar to the Osthoff shape, although slightly less straight on the inside strings.

That's a great looking headstock too. I love how the headstock facia is (or appears to be) the same piece of wood as the fretboard. I don't think I have ever seen that before.

[Alan Carruth]

Thanks Aaron: you got it right.

So long as there's enough break angle at the end of the string so that it doesn't hop off the saddle all of the vibration force will be transmitted to the top. Similarly, at the nut end, once you get 'enough' break angle too stop the string vibrating behind the contact point, more won't help.

More break angle, at either end, will, of course, increase the static forces imposed on the structure. At the bridge increasing the break angle does produce more downbearing, which might help a UST to work better, since they like lots of down pressure. More ominously, it also increases the tipping force trying to break out the front of the saddle slot.

On the nut end the issue with more break angle and down force has to do with increasing the friction between the string and the slot. Iirc, that's going to be the product of the force and the coefficient of friction. Keeping the break angle at the nut down to the minimum, and polishing the slot, will both help.