# How easy would it be to manufacture knotted rubber bands? (Or Moebius strips?) **URL:** \ **Category:** Factual Questions\ **Created:** [November 1, 2020, 5:01am UTC](https://boards.straightdope.com/t/how-easy-would-it-be-to-manufacture-knotted-rubber-bands-or-moebius-strips/924472 "2020-11-01T05:01:23Z")\ **Posts on this page:** 7\ **Page:** 2
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 2, 2020, 10:19pm UTC](https://boards.straightdope.com/t/how-easy-would-it-be-to-manufacture-knotted-rubber-bands-or-moebius-strips/924472/21 "2020-11-02T22:19:22Z")
Yeah, I mean, it would be possible to mould a seamless hollow torus by using something like rotary moulding, where a heated mould containing a torus shaped void is filled with a little of the material to be moulded, then closed together and heated whilst rotating it in multiple axes - the material melts and coats the inside of the mould, then continually rotated while it cools - when it’s pulled apart, inside there is a single piece hollow form. But I just don’t think anyone does that, for hollow torus shapes made from rubber. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [November 2, 2020, 10:51pm UTC](https://boards.straightdope.com/t/how-easy-would-it-be-to-manufacture-knotted-rubber-bands-or-moebius-strips/924472/22 "2020-11-02T22:51:46Z")
Hey, looks like only 1 other person has clicked on that Superconducting Quantum Levitation video I linked a few posts above. Ya all gotta see that! It’s awesome! (IMNSHO of course.) ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [November 3, 2020, 7:25am UTC](https://boards.straightdope.com/t/how-easy-would-it-be-to-manufacture-knotted-rubber-bands-or-moebius-strips/924472/23 "2020-11-03T07:25:43Z")
> [@glowacks](#): > > > [@Mangetout](#): > > > > I’m not sure you’re going to find a seamless rubber torus though > > Yeah, a bit of investigation shows that it’s not a solid torus they’re talking about, but the surface of one. Those would require a different manufacturing technique than forming a long solid but thin torus as shown in the video, and if you’re saying that the manufacturing of the actual products that are of that shape and topology requires joins, it’s probably not the route to go. Which video? [Here](https://www.simonsfoundation.org/2013/01/03/mathematical-impressions-knot-possible/) is the video demonstrating how to cut a solid torus into a knotted band. ---
**Author:** ![Keeve](https://avatars.discourse-cdn.com/v4/letter/k/f07891/32.png) [@Keeve](https://boards.straightdope.com/u/Keeve)\ **Post date:** [November 3, 2020, 10:55am UTC](https://boards.straightdope.com/t/how-easy-would-it-be-to-manufacture-knotted-rubber-bands-or-moebius-strips/924472/24 "2020-11-03T10:55:39Z")
> [@DPRK](#): > > [Here](https://www.simonsfoundation.org/2013/01/03/mathematical-impressions-knot-possible/) is the video demonstrating how to cut a solid torus into a knotted band. Great video. Thanks! I would point out that he started out with a rubber band that had a circular cross-section, rather than the much more common flat bands; the rotation of the knife would be extremely difficult with a flat band. Having cut the circular cross-section down the middle, the resulting knotted band has a D-shaped cross-section. I suspect that the surface of the flat part of the D is now a moebius strip, and that’s the secret of how this magic works. Is that correct? ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [November 3, 2020, 2:48pm UTC](https://boards.straightdope.com/t/how-easy-would-it-be-to-manufacture-knotted-rubber-bands-or-moebius-strips/924472/25 "2020-11-03T14:48:53Z")
There is an extra full twist in the surface compared to a usual Moebius band, unless I am mistaken. ---
**Author:** ![glowacks](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/glowacks/32/5548_2.png) [@glowacks](https://boards.straightdope.com/u/glowacks)\ **Post date:** [November 3, 2020, 10:22pm UTC](https://boards.straightdope.com/t/how-easy-would-it-be-to-manufacture-knotted-rubber-bands-or-moebius-strips/924472/26 "2020-11-03T22:22:40Z")
> [@DPRK](#): > > [Here](https://www.simonsfoundation.org/2013/01/03/mathematical-impressions-knot-possible/) is the video demonstrating how to cut a solid torus into a knotted band. Ok, thanks, I was just having a failure to visualize it properly. It’s obvious now that I’ve seen it. I thought the construction of it went completely differently, where you merely cut out a section of the torus that is formed into a loop. This shows you have 100% yield if you start with a thick enough band such that the cuts can work. You just need to have the extruded material have a significant thickness, and this construction should be easily doable by machine. A problem I’m not sure how to solve is how to get the cross section into a shape that doesn’t make it look like it was cut in the way it was. The resulting shape of the cross section starting with a circle is always a half circle, but because of the twists, you can’t start with a rectangle twice the size of a square and get a square out of it unless the orientation of the rectangle changes along the length in a way that’s basically like a Moebius strip (except with 3 twists instead of 1), which means that you now need a way to manufacture a 3-turn Moebius strip first or accept that you’ll end up with something that looks like it’s been cut. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 3, 2020, 11:28pm UTC](https://boards.straightdope.com/t/how-easy-would-it-be-to-manufacture-knotted-rubber-bands-or-moebius-strips/924472/27 "2020-11-03T23:28:13Z")
So what you do is, you first get a bunch of toroidal (with circular cross-section) rubber bands, and you cut all of them in half with a non-twisted cut. Make lots of these, and get them into the supply chain for your company. If anyone asks why they have a D-shaped cross section, shrug your shoulders and say “I dunno, that’s just the way they make them”. Then, once they’ve gotten used to them, then you spring your twist-cut bands on them. [Previous page](https://boards.straightdope.com/t/how-easy-would-it-be-to-manufacture-knotted-rubber-bands-or-moebius-strips/924472.md?page=1)