3

String and rope are usually composed of a few smaller threads twirled into a larger thread:

Twisted string

This causes the resultant string to tend to twist itself one direction more than the other. In addition, when twisted in the direction opposite to the twirl, the string will unravel itself, and the result is ugly.

Are there string that has been twirled in a chirality-neutral manner (i.e. the string does not have an intrinsic "left/right-handedness"), so that it won't unravel when twisted in either direction?

Googling "chirality-neutral string" and "non-handed string" doesn't yield any good results, but obviously I'm not getting the name correct.

| improve this question | | | | |
  • What about braided cord? It's woven instead of spun, so it wouldn't separate due to twisting. You can get pretty thin and strong cord nowadays too (like paracord). – user812786 Jun 20 '17 at 12:21
  • Yes, I think braided yarn might be the answer! I don't need it to be particularly strong, so normal yarn should work. Thanks! – Bernard Jun 20 '17 at 12:30
3

You don't say what you are trying to make or do so I can't help there, but what follows addresses your question about twist in string.

String is technically a yarn.

The two major classes of yarn are Spun and Filament.

Spun Yarns are composed of individual fibers that are "spun" (by various means, manual and mechanical) together into a longitudinal structures called a yarn. What holds the fibers together? Why doesnt the yarn just fall apart into loose fiber? The physics that hold the loose fibers together is supplied by twist. Low-twist yarns are looser and less stable than tighter yarns - think of a loose fluffy (low-twist) yarn in a soft sweater vs. a tight (high-twist) yarn that is woven into a smooth dress shirt fabric. Even sewing thread is technically a yarn and has twist for strength and stability.

Filament Yarns are zero-twist yarn structures. Filament yarn is extruded (again, via various methods) and is not composed of fiber held together with twist. Examples are synthetic monofilament like fishing line, and the monofilament that is used to weave some outdoor fabrics and furniture, and some types of indoor-outdoor carpeting.

The twisted string structure you show in your question looks to be two yarns simply twisted together. The twist in the red and black yarns holds each of them together individually, but simply twisting the two yarns together does not produce the physical cohesion between the two structures that mimics the twist imposed in a fiber spinning process. That's why ropes and braids will easily unravel.

This is a simple explanation, it's possible to get a material science PhD in the physics of textile spinning, so there is much more info out there.

Hope this helps.

| improve this answer | | | | |
  • I'm trying to use one thread of yarn (about this width) to connect a light hanging object to a fixed object. The two ends of the yarn will be glued to the objects. However, due to the design of the hanging object, it is ugly if the hanging object is rotated significantly (with respect to the fixed object) at rest, and spun yarn tends to rotate after a while. Filament yarn is definitely not what I had in mind - it doesn't have the soft, hairy feeling expected of string. Is there no way to twist the yarn in a neutral manner? – Bernard Jun 20 '17 at 7:39
  • The objects will be 3D printed so I can customize them exactly as required, but I don't think this will change anything. – Bernard Jun 20 '17 at 7:39
3

(this was too long for a comment…) Thanks for the explanation of your project.

I suggest using a yarn called Chenille. Chenille is not technically a “yarn” in the sense that it is not composed of fiber spun into a yarn with some level of twist as is traditional, but it serves the same purpose in that it can be knitted and crocheted into soft and fluffy items such as sweaters and scarves and baby blankets. Chenille is an old technology/structure that in the past was used commercially to produce chenille bathrobes or bedspreads, which have been out of style for quite a while.

The following video starts with a good explanation of what a Chenille yarn is, with a comparison to traditional yarn. Chenille yarn is made like a pipe cleaner - short fiber is attached to a core which anchors the short fibers without requiring twist. Chenille yarns are very fuzzy, not very strong, and the softness depends on the type of fiber used. Acrylics can be very soft and fluffy. The drawbacks of Chenille are that it is low strength and can shed (the small fibers fall out of the structure), but for your project, it sounds like you need zero-twist more than you need strength.

Most Chenille yarn for home use is typically large and bulky so that it can be quickly knitted or crocheted into the final product. Michael’s is a good source for these. The second link is a source for fine Chenille yarn which looks like it might be the size you are looking for, and is offered in several colors.

Good luck with your project - it sounds very cool!

https://www.youtube.com/watch?v=kkTtIYs38ag&spfreload=10

https://www.yarn-paradise.com/thin-chenille-emerald-green-fnt2-50467

| improve this answer | | | | |
  • Thanks for the suggestion! I think I saw some Chenille before, just that I didn't know what it was called. This might also be suitable - looks like some sort of braided bunches of filament, but the braiding seems to make it soft. I'll probably go to an art and craft store to look at and feel the various strings available. – Bernard Jun 21 '17 at 4:44
2

As @abbie has explained, yarn is created by using twist to "stick" short fibers (of wool, or cotton, or hemp, or linen, or...) together to make a longer strand. When you spin yarn, you have to add twist to connect all of the shorter individual fibers together into a continuous longer piece of yarn. The more twist you add, the stronger the individual strand of yarn will be. Yarn that is made from one bunch of fiber twisted together is called single-spun, or is known as "singles".

Spinners talk about a twist as having energy; imagine a spring--when you push down on the spring you are building up energy, and when you let go, the spring pops back up to its neutral position, releasing that energy. Single-spun yarn with a high-level of twist is called "energized" and will tend to want to kink up on itself, and even after it is knit or woven into a garment, it will create an uneven fabric. This bag was knit with energized singles to, as the blog author put it, "create deeply textured effects." enter image description here

It is the energy created by twist that leads a cord to want to untwist--it is trying to release the built up energy by untwisting. The way that spinners deal with this is that they twist two singles together in the opposite direction of the first spin. Because you are twisting the two strands in the opposite direction from the original twist, the energy that would go towards untwisting tends to balance out. This process is called plying, and the goal is to create "balanced" yarn. You can tell that a yarn is balanced by letting a loop hang--if it hangs freely, without forming kinks, it is balanced.

You mention in the comments that you are going to try using a braided cord, as per @whrrgarbl's suggestion. If you can't find a braided yarn that will work for you, another suggestion might be to double the strands that are hanging down--i.e. cut a piece of rope with a distance twice as long as the distance between the ceiling and the top of the lamp. Slide this cord through a hook (either on the lamp or the ceiling) and knot the other end together. The two strands of the cord should work against each other and keep the cord from untwisting.

I know this goes far beyond what you needed to solve your particular problem, but I wanted to add more detail to better respond to your question about "chirality-neutral" string, and why there really is no way to "twist the yarn in a neutral manner."

| improve this answer | | | | |
  • Thanks for the info! Not so sure if "balanced" yarn would prevent the spinning. Braided yarn/filament feels like it would have the most resistance to twisting at rest (as compared to "balanced" yarn and possibly even Chenille), so I'll probably give that a try first. Also, I realized that while I intended the "light hanging object" I mentioned in my comment to the other answer might be taken to mean the opposite of heavy, it might be taken to mean the thing that emits electromagnetic radiation in the visible spectrum. I think you might have interpreted it as the latter; sorry about that :/ – Bernard Jun 21 '17 at 14:20
  • I wasn't at all confused by your use of "light," but I appreciate the clarification just in case. I agree that going with braided yarn is going to be your best bet--even a balanced yarn will definitely want to unspin over time. That's why I suggested using a double loop of yarn if the braided yarn doesn't work out, once you loop the yarn, the two ends will essentially be wound in opposite directions, and their tendency to spin will hopefully cancel each other out. – magerber Jun 21 '17 at 21:30
  • Could you please elaborate on the double loop? If I take a piece of right-handed yarn and flip it, the yarn would still be right-handed, so the tendency to spin is still in the same direction, no? – Bernard Jun 22 '17 at 10:28
  • There are two types of twist - S and Z - and no matter which end is "up" that orientation remains. You'd have to find one of each to try and make this work. 😉 – user1798 Jun 22 '17 at 13:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.