String clamping methods

ed packard · From: Show Low AZ

On the “traditional” PSG, the string has a ball end with a wrapped section of string/core to hold it. This ball is slipped over a pin that is on the back of the changer finger. The wrap then presses against the back of the finger, and sometimes approaches the top of the finger. My apologies for the darkness in some of the photos…too lazy to retake them at the moment.

The other end of the string passes through a V grooved roller nut (of various sizes and materials) and is wrapped around a “tuning key” that tensions the string to pitch. The distance from the roller nut to the tuner key is around 6 inches for the center strings, to as little as an inch for the outer strings.

One variation on the theme is the slotted changer finger, in which the string ball slides into the slot that replaces the pin on the back of the changer finger.

Later modifications replace the “tuner keys” with the “keyless tuner”. The keyless tuner comes in several flavors, most of which clamp the string via a screw at the nut end. Some of these require routing the body top, and some of which bend the string sharply around the nut, and/or across a sharp edge; the ones that don’t tend to take up a bit more space. Typical string length beyond the nut is about a half inch or less. The keyless tuner gives a ratio of scale length to total string length that is nearer the same for all strings, and also closer to the same value for all strings.

Balls and wraps on the 0.011” diameter strings are a source of string breakage. If we could do away with the ball & wrap there could be several advantages:

1. There would be less small string breakage.

2. Straight lengths of piano string would mean more gauges available. Some 14 stringers should use 0.120” diameter low end strings.

3. There would/should be a cost saving at the same manufacturing volume.

4. No balls to fall into and jam the changer.

What can be done to make the ball & wrap unnecessary? One could clamp the string under a screw at both ends. The pin and the slot on the changer finger could be replaced with a screw at the top back face of the changer finger. This would cause a centering the string on the finger issue (if one cared about centering). This is solved by a small pin placed near the screw around which the string is routed to place it near the finger center. The screw head shape/type is a matter of choice. I did not have a small pin so it is illustrated with a drill bit in the photo.

What can be done to place the keyless tuner close to the roller nut (assuming that rollers are desired), and to reduce the need for added body length beyond the nut? Alternatively, a longer scale length with more frets is possible.

A simple short finger with pivots installed can be anchored to the bottom of the plate that holds the roller, or rod, or whatever is chosen to be used for the nut. All the slot and groove machining in the nut holder in the photo would then be unnecessary.

Strings with ball & wrap could still be used…just snip off the ball and wrap and use what remains with the screw clamps.

For the more adventurous, the keyless tuner can be integrated into the changer finger. The one shown below uses the ball & wrap. With a bit of thought, the screw clamp could be added to the finger. Feel free to post your opinion(s) and creations.

The nut end now becomes simplified.

Violent reaction is expected from the extreme traditionalists. Violence seems to be associated with extremism everywhere…luckily here, it is limited to words.

For those that might want to splash around in a variety of PSG photos & "stuff":

http://s75.photobucket.com/albums/i287/edpackard/

Justin Griffith · From: Taylor, Texas, USA

Interesting Ed, Keep us posted

Earnest Bovine · From: Los Angeles CA USA

Ed
The string hardly bends at all as it passes over the finger. I'm sure you did this delberately, but did you experment with a sharper bend in the string as it passes over the finger? In your example, the component of force pushing the string onto the changer is very small. So the string is not firmly anchored at the finger, and may wander side to side, damping the vibration.
I wonder if the tone might be better if you were to pull it down more.

ed packard · From: Show Low AZ

Doug...pleasure to see you at the Mesa show.

I intentionally kept the string angle shallow to see if the "tone" would change re the same instrument with the ball in slot approach. The Frequency Spectrum Analysis comparison (and my poor old ears) of the two did not show any differences under the test conditions. The issue was hard vs. soft string termination comparison.

Re wandering string position...if one worried about this, adding the pin (see the screw clamp for changer finger photo) can be used to "center" the string and provide a piano like string termination. I assume that that would be classed as a "hard" termination. Edited for after thought...I moved the second string to one side on the finger (combined tuner/changer photo) to show the small groove that positions the string...contrast makes it too hard to see. It is made by placing a piece of the string on the finger, and pressing it in = dent.

About string location: using the string spacing centered with different string gauges means that the "picking" distances between strings is not a constant...it never bothered me, but then nothing could make my playing any worse.

Just to get far off topic, have you ever worked up "Classical Gas"?

Tom Olson · From: Spokane, WA

Colby Tipton · From: Crosby, Texas, USA

What Earnest said, plus it looks like if you had the least little bit of a groove you would have the sitar buzz effect going on. I think it is to straight, you need to have some downward angle. I'm traditional and think it is a good idea, it is a move in the right direction, I wont slam you on a good idea. You have to make sure that all of the screws on one area do not move and flex are you will be in big trouble with wear and tare. Everything that you have to tune with needs to be one tool also.

Ron ! · Posted 5 Feb 2007 6:24 pm

I think that one of the ways that you could go is an upright changer unit.I am working on one right now.The force that you need to make the string raise is what bugs me the most.Lowering the string is not that hard.Now to make that unit easy adjustable and light is another thing.
MHO is that a string that is straight has less string breakage and has a more clear tone.The same thing can be done with the "Tuning Key".
Ed is one of the guys here that is studying this subject for as long as I know and brought very good idea's in our community.A highly respected man with a lot of Maths in his brains.Keep up the good work Ed.

Ron

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Requiring a screwdriver or allen wrench to change a string just doesn't seem like progress to me. At least with a standard slot or pin, we don't really need tools to change a string.

I'm often thought that a small spring-loaded cam jaw might work. No other attachment (as in a loop or ball) would be needed, and the more tension put on the string, the greater the gripping force would be. (Similar methodologies are already used to hoist steel plates in the construction industry.) I'm not sure about how well the idea would work with wrapped strings, though? Rolling Eyes

Getting back to the wrap length problem, that could easily be negated with an alternate design, such as the thread-thru type the later Fender steels used. With even the best steels made today, I still see a lot of room for improvement. Confused

Colby Tipton · From: Crosby, Texas, USA

Spring loaded cam. That is a good idea. You would have to hold tension untill you got the string tight enough to make the cam hold. Am I wrong or right, spring or not?

Tom Olson · From: Spokane, WA

I don't know really how much this applies to the topic at hand, but for what it's worth --

The fact that a string is bent, kinked, or curved as a means of assisting or facilitating the attachment of the string to the guitar has no bearing on metal fatigue (i.e., string breakage).

What DOES affect string breakage (at least in a psg context) is the number of times and the degree to which the string is bent back-and-forth, kinked back-and-forth, or curved back-and-forth. In other words, the more times the string is bent from one position to another and the greater the degree of bend, the faster the string will become brittle and break.

So, in other words, simply having the string in a bent, kinked or curved position as a means of fastening the string to the guitar will not matter -- but any back-and-forth deformation of the string will matter a great deal.

ed packard · From: Show Low AZ

Earnest…You are causing me to lose sleep…thanks for the “challenge” re string angle. Feel free to ignore or respond as you see fit, same for anyone else.

Just some thoughts on the string “angle” issue:

The string will come away from the top of the changer finger at the same angle if…the radius of the finger, gauge and tension of the string, et al are kept the same, with the exception of some “overshoot” that would be a function of the “Angle”= increased string stiffness gives less front of the changer finger contact for less wrap angle.

There tends to be scuff marks develop in front of the apex of the changer finger from the string moving back and forth across it. The max pressure is at the point where there is an equal angle of the string before and behind the changer finger radius. This is not where the scuffing shows up.

In the pin/slot method, the string/ball/wrap pushes against the back of the changer finger, thus damping the behind the finger string vibrations; in the shallow angle approach, such is not the case.

If the finger radius is made smaller, the string will leave contact with the finger sooner, hence giving less of a damping effect.

If the finger radius is truncated at the finger apex, there will be no “front of the finger” material for the string to rub against, but the string length will change slightly when a change is activated. Anapeg and Excel live with this in any case, and apparently without picker complaints. We have gone thru some of the cents off numbers in other posts/threads.

The same shallow angle exists when ever the round bar is placed against the strings…if the bar is smaller, less “scuffing/damping”. The extreme “fix” would be to use the old flat bar with about a ¼” radius…I think that a different tone would be heard.

Now we can go to the Nut end…Same angle/radius issues here for open strings…smaller diameter roller/nut = less scuffing/damping; how about the effect upon the tone (like the flat bar). Roller nuts come in many sizes and groove styles = tone differences?

If grooves are allowed on the roller nut, why not on the changer finger? I intentionally dent the top of the changer finger to constrain the string in place.

Some further comments on the tuner finger:

The shape shown was chosen so that it could be attached to the changer of the instrument I had available without removing the changer from the instrument. If it was built in before the changer was installed, some changes would be made.

Up here in the hills of AZ getting machine shop materials, and even machine screws is difficult, so the first mod was done on $100. drill press, sander, band saw from Ace, and Home Depot.

Refinements on the tuner finger would include a finer thread on the tuning adjustment…I was stuck with 4-40. A larger diameter knurled knob and/or with the center machined out to allow using the socket head screw with an Allen wrench; Girly, and girly men’s fingers might not like the strain (thank you Mr. Arnold S). This does not have to be another tool; I use a very short Allen stub press fitted into the back of the George L wrench used for tuning the change rods.

Cam locks et al:

Donny H: I tried to find a “vice grip” like thingy to use, but without success. There are thumb activated clamps that have the right principle, but are the wrong size….so I opted for the simplicity of the screw head clamp approach. With Allen stub in the George L wrench = one tool that is required anyway.

I don’t think that you would have any trouble clamping the wound strings with the approach that you envision as long as you clamp both the core and the winding.

Ron S…thanks for the kind words…one must spend their allotted time between the cradle and the grave somehow…I like playing with (sometimes on) the PSG.

The metal fatigue factor:

Tom O…I believe that the fatigue issue is part of the subject. Here is my take on it.

How the string is clamped, the tension on the string, and the bridge shapes that it passes over will determine the degree of fatigue that will be induced by whatever vibrations are present. Any notches, scratches, etc. will lower the point of fatigue related failures. Sharp edges on clamp screws can be a source of notches, hence of fatigue enhancement.

The 0.011” diameter string (G# usually) at tensions from 28 thru 33 or so pounds pull is fast approaching its “tensile stress” limit. Any corners that it must go around adds “shear stress” to the problem…sharper corners = more shear stress. The tendency of the string to develop “micro cracking” at the surface as a function of bending will lower the threshold of failure due to the shear, and also lower the threshold of failure due to any fatigue caused by vibration = the basic function of the string is vibration. This is a more likely cause of string breakage for small strings that have a large surface to volume ratio.

The moral of the story is minimize the amount of stress and fatigue concentration sites along the route of the small diameter strings in particular.

Theory or practice?...mental manipulation or measurement.

The tuning finger and tuning finger/changer integration presented above has been used as the basis of several SIERRA session series instruments…all 14 stringers, and all in different ways. The sonic performance (frequency content, and sustain) have been measured and compared with 32 other PSGs. Photos of the instruments will be added to those shots above soon (a day or two).

The sonic performance charts will be referenced to the Photobucket site mentioned on the first post of this thread…you can find them now if you want to splash around on the site.

Tom Olson · From: Spokane, WA

Ed, yes I agree that any type of stress riser (e.g., nicks, gouges, cracks, etc.) in the string will increase the probability that the string will break at that stress riser. For example, strings on fretted instruments will often break at a point where the string contacts one of the frets, and where that contact has "dented" the string.

And, I also agree that a bend or kink that is too sharp will act as a stress riser. However, I think the bend would have to be a very small radius before it begins to act as a stress riser. As an example, the radius of the string bend around a ball end is very small, yet I'd be willing to bet that the string hardly ever breaks as the result of this sharp bend around the ball end.

I might be wrong but I don't believe that the vibrations of the string will cause much, if any, amount of fatigue in the string. That's based on my belief that in order to have metal fatigue the stress in the string must approach or reach its yield stress. I don't think the natural vibrations of a string would result in the string approaching its yield stress if the guitar is properly designed.

Tom Olson · From: Spokane, WA

Ed, yes I agree that any type of stress riser (e.g., nicks, gouges, cracks, etc.) in the string will increase the probability that the string will break at that stress riser. For example, strings on fretted instruments will often break at a point where the string contacts one of the frets, and where that contact has "dented" the string.

And, I also agree that a bend or kink that is too sharp will act as a stress riser. However, I think the bend would have to be a very small radius before it begins to act as a stress riser. As an example, the radius of the string bend around a ball end is very small, yet I'd be willing to bet that the string hardly ever breaks as the result of this sharp bend around the ball end.

I might be wrong but I don't believe that the vibrations of the string will cause much, if any, amount of fatigue in the string. That's based on my belief that in order to have metal fatigue the stress in the string must cross from tensile to compression many times, or perhaps the stress must approach or reach its yield stress (but maybe in this latter scenario, I'm actually thinking of stress fractures). Anyhow, since the strings are "pre-stressed" by being under tension, the stress will not cross from tensile to compression, and I don't think the natural vibrations of a string would result in the string approaching its yield stress if the guitar is properly designed. So, that's why I don't think string vibration, by itself, contributes to metal fatigue in the string.

ed packard · From: Show Low AZ

Tom...good points...we are basically in agreement. The major problem string is the 0.011" diameter one, and per response given in another thread about a month or two ago, concensus is that they tend to break at the wrap area above the ball. This is a tight wrap, and may have been pressed into the core. This string is close to the yield point when tensioned to 33 or so pounds. This is therefore a main problem to be considered in string clamping. The screw head clamp is one possibility...got any ideas?

One good thing would be to eliminate the need of the ball and wrap.

Is it drying out in Washington yet?

ed packard · From: Show Low AZ

Here is what the above modifications have resulted in so far, and how it got to this point.

The first step was modifying an existing instrument with home made parts.

1. The tuner finger was designed, made in brass, and integrated into a changer.
2. The roller nut end was replaced with a wood block and aluminum plate; string clamps were screw heads.
3. The neck block was not removed. The string spacing was set to 11/32” at both ends.
4. The tuning was E9/B6/A6/E13 series.
5. The sonic performance was tested before and after the modifications to verify that no disastrous effects had been created/caused.

The next photo shows the changer end of the home modified instrument.
The second photo shows the nut end of the home modified instrument.

The second step was to have the modifications put into the desired form by the instrument maker…thanks Don C and Tom Baker.

1. Tuner finger integrated into changer.
2. Scale length set to approx 30”.
3. Changer tuner moved to players left.
4. Nut end (pickup end in this case) made as block and rod with screw head string clamps; string centers set to 11/32” at both ends.
5. Two removable pickups installed.
6. Neck block removed, replaced with rails to hold the fretboard.
7. The tuning was set to C9/G6/F6/C 13 series.
8. The sonic performance was tested for comparison with the tests on the first step instrument, and also against 32 other PSGs.

The next photo shows the pickup/block/rod end of the instrument.
The second photo shows the changer/tuner end (players left) of the instrument.

The third step is/was to modify an instrument to expand the 13 series tuning setup into the “SONIC PALETTE”. A 25” scale length, standard neck block, standard tapered string spacing was chosen, with the changer/tuner placed at the players right. The standard roller nut, and the manufacturer’s keyless hardware were used. The keyless tuner adjuster screws were left out. The reason was that the tuning setup is the point of interest for this third step and this approach was/is the fastest easiest way to proceed.

Those interested in the tuning evolution can see the details in Forum threads containing the term SONIC PALETTE.

The first photo below shows the Changer/Tuner end of the instrument. The second string has been moved aside to allow seeing the string dent intentionally made in the changer finger to hold the string centered.
The second photo below shows the roller nut end of the instrument.
The last photo shows the tuner finger adjusting screws sans knurled knobs. The George L tool is shown being used as a tuning adjuster…the other end is the changer rod adjuster,

It may be noticed that the screw head string clamp does not nee diagonal pliers/nippers to remove the remaining string length…just wiggle it vigorously back and forth to break it off. BUT if you may want to remove the string and use it again, leave some sticking out. No string yanker is needed with this approach.

What will be next? Probably modify the instrument presently dedicated to the tuning/setup project to a NO BALLS piano (pin and screw heads) arrangement, at both ends, with the tuner finger attached to the nut end, a finer tuner finger thread, and the knurled tuner finger knob machined out to allow using either the knob and the underlying socket head for tuning purposes.

Tom Olson · From: Spokane, WA

Ed --

Actually I do have an idea for attaching strings, but I don't know how practical it is.

Consider, as I mentioned above, the fact that a string rarely, if ever, breaks at the tuner post. Yet, at the tuner post, the string is kinked where it goes through the hole in the tuning post, and then is bent in a small radius around the post for a number of "wraps." The wraps of the string create enough holding force to prevent any significant amount of the string tension from reaching the "kink", and so the string is held securely on the post.

I believe a similar concept could be implemented succesfully on the bridge end of a guitar. For example, imagine a small diameter post with a hole through it and with an allen head (or something similar) key on the end of the post. Also imagine that the post can rotate, but also has some sort of locking mechanism to prevent it from rotating. One exemplary type of locking mechanism would be to simply have fine machine threads on the end of the post so that when the post is turned a certain number of times, it "locks down" from the threads tightening.

So, let's say you have the type of post described above. First, you take your allen wrench and back the post out about 3 or 4 turns. Then, you take your string, you thread the string through the hole in the post and pull it through so that the ball end is pulled up against the post.

Now, you thread the plain end of the string through the tuner at the other end of the guitar and take up the slack, but not all of the slack.

Now, you take your allen wrench and turn the post on the bridge end of the guitar until it bottoms out so it's fully threaded into whatever it's threaded into, and so it's tight. In the process of turning the post, you've wrapped the ball end of the string 3 or 4 times around the post.

Now, you bring the string up to proper tension with the tuning mechanism.

Like I say -- don't know how practical this is, but in my opinion, it would help eliminate any type of string breakage that could possibly be attributed to the ball wrap.

Also, other types of locking mechanisms are envisioned. The one described above is perhaps the simplest.

ed packard · From: Show Low AZ

Tom...I can envision that...are you going to try one?

Further to the "breaking" mechanisms; The 9th string on some E9/B6 Uni's is often changed from Bb to D = 4 halftones. It tends to break after a while from the "pumping", at least on the slot or pin attachment method. I am not sure where they break as I do not use that change. I assume that they would break at the apex of the changer finger.

Tom Olson · From: Spokane, WA

Ed -- no, I'm not a builder nor do I have the time to mess around with it. Most importantly, I don't have any problems with the strings breaking at the ball ends, so I have not motivation to try it. Smile

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