Glue to remedy unraveling string loops

For the first time, I tried the trick of applying Gorilla glue to an unwinding string loop, and after one additional time of tuning up, it held!

I wonder what the experience of others has been using this fix. Is it relatively permanent?

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Le 14/12/2022 18:01, Keith Womer via The Jackrail écrit :

For the first time, I tried the trick of applying Gorilla glue to an unwinding string loop, and after one additional time of tuning up, it held!

I wonder what the experience of others has been using this fix. Is it relatively permanent?

What type of string? Brass?

I use super glue (cyanoacrylate). It also works and I prefer it to Gorilla Glue.

David

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Yes, brass. Lowest D#.

Le 14/12/2022 18:34, Keith Womer via The Jackrail écrit :

Yes, brass. Lowest D#.

Was this Rose wire by any chance? It happened to me on at least a half a
dozen of brass strings, very strangely several years after they’d been
played and tuned regularly. I tried super glue on a couple of them, but
I think it was already too late, so I ended up changing them. Never
tried Gorilla glue.

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David,

Thanks for the info on cyanoacrylate. Have you found this to be a permanent or a temporary fix?

https://www.woodworkersjournal.com/permanent-cyanoacrylate-glue/

In passing, most glue manufacturers make several different types of glue. I respectfully suggest that just giving a manufacturer’s name is insufficient.

Frank.

Yes, it was Rose wire. And installed as part of a complete restringing by Don Angle. So, I think I can discount improper loop construction.

Like you, this starting happening to me 3-4 years later. After losing about three, I thought I’d try the glue solution (which I heard of through the e-grapevine), which for the moment is working.

Replacing the string works, of course, but it does take an annoyingly long time for the replacement to fully stretch out.

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Rose wire slowly stretches indefinitely. This causes the hitchpin loops to get to the point where they unwind. A drop of cyanoacrylate helps. Be sure to place something under the loop such as a bit of wax paper to catch any excess. A double loop start to the hitchpin loop can also be helpful when putting on a new string in preventing such unwinding.

I have heard that some modern wires, made of an alloy of two metals, favour this problem. Historical wires, alloys of metals which included a significant amount of “minority” impurities of other metals, were not only stronger but also unlikely to “stretch”.

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You are probably right. As a matter of fact, Stephen Birkett’s historical wire - p-wire (iron) AND brass - are known for not stretching, or minimal stretching. That has been my experience too.
Malcolm Rose’s brass does stretch a lot.

Dom

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Permanent. I just put a piece of paper underneath the coil, in case of drips, and a drop of superglue along the coil. It sinks into the twists easily. If necessary to spread it, a toothpick is an excellent disposable tool.

I have had this effect with older Birkett brass. It has never happened to me with iron strings and is so rare that I just take it in stride.

David

David

This week I used CA glue to hold a string in place for the initial turns on an 18th century pin with no hole. Worked a treat.

I have been following with interest the disscussion on fixes to prevent slipping of strings around hitchpin(s).

About 8 years ago I was in a phase where an unusual number of slippages occurred in the base section (brass wires). I remember having “heard” (I cannot remember how or where), that in his later years Frank Hubbard (or his succesor?) had gone over to using a “second loop” for the strings. I thought at that time, that this might not be acceptable to the purists in Harpsichord construction and maintenance. But as I learn now of how many today resort to using “strong glues” (which were not available in the baroque period), the benefit of an additional loop (Anne Acker) might be worth evaluating quantitatively as a guaranteed replacement remedy. I recognize, that the glue-approach is “easier”, if not as durable.

Being mindful of holding large ships via ropes wrapped around capstans, I resurrected my sophomore mechanics and calculated the effect of multiple loops (in the harpsichord case a single extra loop suffices). I also remember since my experimental physics class that vibration is typically a source for reducing friction, e.g., allowing a weight to slip down an incline and stop when the vibration ceases.

We are interested here in assessing how much more pulling force is achieved before slipping occurs, if one adds one or more turns around the hitchpin (even if that theoretically exceeds the physical strength of the string). The analysis contemplated is conservative in the sense, that other energy-losing mechanisms operate (e.g. plasticity) that work in the same direction as the friction between the string and the hitchpin (thus effectively increasing the friction), so that the current analysis is a low estimate.

For further clarity I shall use the term “vibrating string” as the highest (longest) pull carrier and the term “end” for the short wrap-around at the pin and twisted together with the vibrating string. Let me call the force in the vibrating string “Fv” and in the end close to the pin, “Fe”, with the former being always larger that the latter, the difference being carried by the friction between the string and the pin. Regardless of the details of how closely the “single wrap” is accomplished to where the vibrating string and the end come together for the wrap, that part of the problem is not primarily important if we consider that portion of the string configuration to remain the same.

The effect of adding a number of wraps: To avoid scaring anyone with too many equations, it suffices to state that the increase in the friction force afforded by a single (additional) turn, before slipping can occur, is given by an increase in the ratio of Fv/Fe = exp(2muπ). Here “mu” is the coefficient of friction between the string and the hitchpin (mu = 0.35 for steel and brass, and =0.5 for steel on steel; see the Footnote) and “π” = 3.141 . The expression exp(…) signifies the (Euler) number “e” = 2.718 raised to the power of the number in the parentheses.

For a brass string this expression yields then a minimum increase in retention by a factor of about 10 (calculated =9); for a steel string that factor increases to 23. Note, that according to the foot note this number may climb close to about 20 for brass on steel! I have no way of readily estimating the effect of vibration on this result. But I would argue that the tremendous increase in the holding power, when applied to the real-world experience, speaks for itself.

In this context it may be of interest to also estimate the force Fe provided by the wrapping of the vibrating part and the end portion of the string at the point of incipient slipping, using a “single” loop with a string-pin contact over about 225 degrees on my harpsichord. For a brass string this force would be at least about 1 ¾ kg according to Claudio di Veroli’s string force table of about 7 Kgs in the bass (https://harps.braybaroque.ie/restringing.htm), a ratio of close to 4, leaving the force of the twist arrangement the same. The extra wrap around the pin thus increases that ratio at least to 40!! Remember, this is the lowest estimate. I do not think that all my installations of new brass springs will slip during my life time (none of my steel strings have slipped, ever!).

Footnote: This is the minimum value for the steel-brass combination, with the maximum being 0.5. For steel-on steel the range is 0.5 to 0.8. http://www.structx.com/Material_Properties_005a.html

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