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.
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.)
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?
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.
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.