How far does a string strech to change pitch?

[Karlis Abolins]

Has anyone done a spreadsheet on the amount of stretch required to raise a string of given tension and scale length by a half tone, a whole tone, a tone and a half? I am blue skying a mini changer and would like to know what I would encounter as far as changer motion is concerned.

Karlis

[Andrew Frost]

I've wondered about this too. Some kind of table with core size of string, and how much travel is required to raise and lower by semitone. I imagine it would be tricky to quantify in practical terms though...

[Doug Earnest]

Search here for Ed Packard. He did a great deal of those measurements.

[Bobby D. Jones]

I play a GFI 12U Keyless. I Checked the movement of the strings,
The longest pull is the 9th string raise from B to D.

This may help on chart of string movement.
Scale 24 inches.
The 9th string has a .017 core, Raise from B thru C, C# to D the string is pulled .042 on finger radius to accomplish the change.
The rod tuning nut moves the changer finger .227 in the 3rd hole of the changer finger, To accomplish the D note.

Good Luck on this project.
Edited, I for got to put the scale length in the post and it was keyless.

[Karlis Abolins]

Doug, Thanks for the tip about Ed Packard. I found a thread where he mentions a .04 motion on a 25 inch scale at 30 pounds.

Bobby, Thank you for taking your time to post your values. Your result corroborates Ed's post.

Now that I know the ballpark I'm in, I think I may be able modify one of Terry Down's spreadsheet formulas to give a series of values for scale length and tension. This will help me in designing a mini changer.

Karlis

[Jack Stoner]

I have a GFI keyless. It does not have a roller nut, just a round steel bar. Statement on the GFI site says movement is not enough to warrant rollers. I've only had the guitar since December but no string breakage.

[Bobby D. Jones]

I bought a GFI S12 keyless in 2019-20, Between a heart attack and COVID I just got into playing it around the first of March. I had bought rod stock to make a roller nut if needed.
In March I started setting it up and playing it, I will not change the the chromed solid bar Nut. The guitar has more sustain than any other guitar I have sat down at. I have a GFI S12 with keys and roller nut, It is flat compared to the keyless guitar.

[Donny Hinson]

Karlis, I would think that you'd also have to include the string gauge in the equation, since heavier gauges require less movement to make a certain change.

[Bobby D. Jones]

Karlis, Another value that would have to go into this equation would be, The total length of string from center top of changer finger, To center of key Cap Span shaft, Or attachment point on a Keyless adjuster, For total string pull length.

What brought this to mind.
For 15 years I played a 1970's MSA S10, Built with a 12 string key head, Strings 5 & 6 on its 24" scale, Measured near 30 1/4" of string under tension from center top of changer finger to center of key Cap Span shaft.

From top center of changer finger to string lock screw on a GFI keyless is 25 1/4".

A 5" Shorter string would make quite a difference in the equation.

[Sonny Jenkins]

Lamar Colvin did a lot of those calculations for designing his straight pull changer. The ones I've had movement was very very minimal

[Jim Palenscar]

Terry Downs created a string gauge tension vs. note spreadsheet that was great a number of years ago. In the research that I've done personally the greatest influence is the core diameter however it is also influenced by the wrap. In an effort to minimize cabinet drop w the sixth string I found that using a wound .020 had a .010/.011 as the core(varies by manufacturer) lessened the cabinet drop more than any change. The trade off was the amount of travel when lowering the string was significant and frequently required a longer bellcrank than standard. I used Terry's chart to create a set of tension balanced uni strings and ended up (among other changes)using a .090" gauge string for the 12th string instead of the std .068" in order to achieve a tension of 27# across the neck. It was short lived.

[Willie Sims]

JACK DO YOU HAVE ANY STRING RATTLE ON THE FIRST FRET,WITHOUT GAUGED ROLLERS.

[Jack Stoner]

JACK DO YOU HAVE ANY STRING RATTLE ON THE FIRST FRET,WITHOUT GAUGED ROLLERS.

None that I recall.

Never had any on the Franklin I had for 38+ years and the Franklin does not have gauged rollers.