String stretch length

[Carl Mayer]

Whats the maximum string stretch/slack do y’all design for in the changer(or rotation angle/changer finger radius) to cover any reasonable copedent change? Im thinking through a changer design but don’t want to put it together and find out I can only manage a 2 semitone change. Or if anyone’s got a to scale drawing of a changer finger I can probably figure it out from there

[Tim Toberer]

This is a great question! There are so many factors effecting this namely string gauge. You would want to make your calculations for the string which takes the most stretching to reach the required notes you want to hit. I didn't do any calculations, I actually had to go in and carve way some of the guitar body to allow the changer finger a little more range of motion. My copedant only has single semitone lowers and single semitone raises, and the acoustic design limits the size of the bell cranks. It all works thankfully, but just barely!
I think you would be fine with rough guesstimate though.

[Rich Cottle]

Finger Hole : Yeah my Mullen are 1 3/4" wide and I can get three simitones + or - from the center with about 1/8 " play on each side (all pull changer) , are you making your own changer assembly ? , I would suggest that you just buy one that's already made and then cut your finger hole a little short , most of them are 1 3/4" .

[Carl Mayer]

Yeah Id make my own if I end up going through with it. Jacobus' electro steel builds have me daydreaming about how I can use servo motors. I didnt really like the trolley setup he had and thought a coarse worm gear to drive the changer fingers would work better and make a nice compact setup (see pic). The servos only go 180 degrees though so I have to choose the right worm gear pitch to get as accurate positioning as possible but also cover the note changes I will need.

[Carl Mayer]

I also did some theoretical calculations for some changes (for some other copedent I was thinking about) and they seem to be about .020" stretch per semitone. The calcs leave out the string length outside the scale and some other inaccuracies (like how the winding affects it) so I dont know how much to trust numbers and just wanted some real life comparisons to see if Im in the right ballpark.

[J D Sauser]

Whats the maximum string stretch/slack do y’all design for in the changer(or rotation angle/changer finger radius) to cover any reasonable copedent change? Im thinking through a changer design but don’t want to put it together and find out I can only manage a 2 semitone change. Or if anyone’s got a to scale drawing of a changer finger I can probably figure it out from there

I need to check my notes, but I believe the longest on any "standard" (E9th/Uni or C6th) would be a o,022Wound tuned C6th's A and raised with P7 a whole step.
On my 25" scale keyless I am measuring a "healthy" 3/16" pull on the string to do that! I might be a little more on a KEYED 24 1/4" scale guitar... because the over all string length would be a little longer as it would sit at the 4th key head post on C6th or even further out on E9th.
I would also want to lower that string a whole step (which is less travel, but some changer's rather have lowering limitations than raising).

I used to keep my bottom on C6th D instead of C and still drop it to A with P8... that was the longest lower and only few guitars could do it.

... J-D.

[John Hyland]

.02” (0.5mm) seems very small. I have never tried to accurately measure but 2-3mm seems more reasonable. So I’m in the JD camp. I actually use a screw as the tuner so it would the easy to measure using the number of turns and the thread pitch. I’m about 400km away from my PSG so can’t see what my wound 22 does. My scale length is 24”

[Carl Mayer]

Yeah I thought it seemed too small too. Good idea about just using the tuners though. I’ll try that on mine. Sounds like general consensus is that the 22 wound string is the biggest troublemaker?

[John Hyland]

Yeah I thought it seemed too small too. Good idea about just using the tuners though. I’ll try that on mine. Sounds like general consensus is that the 22 wound string is the biggest troublemaker?

Actually I think you were measuring a semitone of movement - My comment was more in regard to a Tone.
As it turns out - by calculating the running turns it is approx 1.4mm movement for 22w G# to A# ( two turns of a 4mm bolt tuner) and about 1 and ⅔ turn to detune a Tone (1.6mm)

[richard burton]

I've measured the movement of the 4th string full-tone raise on my Marlen.
As it is a pull-release system, the finger is one-piece, and therefore it's very easy to get an accurate measurement.

I measured the movement at the bottom of the finger, and have calculated (by trigonometry) that the degree movement to raise a 0.014 plain string from E to F# over a 3/4 diameter changer finger is 7 degrees 6 minutes (7.1 degrees), which equates to 0.046" travel on the circumference.

[Bobby D. Jones]

The amount of pull required for the string pull at the Changer, Also depends on what type of key system is used on the key head. On Keyed heads some strings like the 5th and 6th string, Has about 4" of added dead string in the key head. This dead string figures in length of string pull.

Some keyless setups like the GFI Keyless have less than 1/2" dead string in the Keyless tuning head. If strings are properly installed.

Just something to figure into your string pulls.

[Bobby D. Jones]

Buddy Emmons C6th tuning has the 10th string 8th pedal lower from C to A. Which is a long change. Takes some calculating on the Lower Return spring too.

[J D Sauser]

Buddy Emmons C6th tuning has the 10th string 8th pedal lower from C to A. Which is a long change. Takes some calculating on the Lower Return spring too.

It's a minor-3rd drop, yes... but it's not a long throw, since that string at 0.068 or 0.070 is fairly wobbly (under-strung).

The biggest drop movements on C6th are lowering the 5 o 6th string a whole step, which only few do.

... J-D.