{"id":36300,"date":"2017-11-21T03:00:19","date_gmt":"2017-11-21T08:00:19","guid":{"rendered":"https:\/\/www.shapeways.com\/blog\/?p=36300"},"modified":"2022-10-17T12:08:41","modified_gmt":"2022-10-17T16:08:41","slug":"tutorial-tuesday-43-leveraging-math-materials-make-bangles-fit","status":"publish","type":"post","link":"https:\/\/www.shapeways.com\/blog\/tutorial-tuesday-43-leveraging-math-materials-make-bangles-fit","title":{"rendered":"Tutorial Tuesday 43: Leveraging Math and Materials to Make Bangles That Fit"},"content":{"rendered":"

Bangle bracelets are great, but they’re so darn bangly<\/em>. A circular bangle bracelet has to be pretty big to fit over your hand, which makes it very loose around your wrist once you get it on. If you think about it, when you use a bangle bracelet you’re wearing it 99% of the time, but pulling it over your hand only 1% of the time. How do you make a design that’s optimized for the 99% instead of the 1%?  The answer is all about flexibility.<\/p>\n

If your bangle design is made of silver or some other metal, then you’re stuck with the shape it is in; it can only be one shape, all the time, and trying to bend it is a pretty bad idea. You can get a circular bangle bracelet that fits somewhat more snugly by printing it with a flex-capable material such as Strong & Flexible<\/a> plastic, since you’ll be able to smoosh the bangle into an oval as you pass it over your hand, and thus get away with using a circle of smaller diameter. But we want to do better than that, and somehow make a bangle bracelet that fits impossibly close around the wrist. One way to do that, if you are using a flexible printing material, is to increase the number of wraps.<\/p>\n

For example, here is a triple-wrap bracelet designed in OpenSCAD. The bracelet wraps around three times without intersecting itself. The code for this design is built on top of the powerful curve-tracing “path_knot” code from power user Chris Wallace<\/a>‘s excellent post on Borromean Rings and More<\/a>.<\/p>\n

\"3D<\/a><\/p>\n

The shape of this curve is a type of Torus Knot<\/a>, but in this case the knot is unknotted, or “trivial,” which means that it can be deformed into one large simple loop. This property is precisely what enables the bracelet to fit so snugly; the bracelet can be put on by pulling it out into a large loop as shown in the video below, and then wrapping it around and over your hand three times.<\/p>\n