Picture of Rotator Cuff Bracelet

Hi all and thanks for checking out my first Instructable! This is a 3D-printed bracelet design that comes in a few different sizes for various wrists. I've been calling it the Rotator Cuff after my mom suggested the name. Here's a short video to give you an overview of the design and show how it works.

Making the bracelet on your 3D printer is fairly straightforward and listed below is a table of contents for the steps involved, along with materials and tools required for each step. The first step in bold is required for proper function of your bracelet, the second step is only needed if your bracelet isn't functioning properly after printing, and the remaining steps are for those who might want to change and customize the design as they please using Solidworks CAD software.

1. Measuring your wrist and choosing the appropriate sized STL file for printing.
     - 3D printer with an X/Y direction tolerance of at least .015 inch (.38mm), preferably .010inch (.25mm)
     - Piece of string at least 8 inches (200mm) long
     - Ruler

2. Cleaning up the bracelet for proper function (only needed if it's not working well after being printed)
     - Small hobby knife (Exacto blade) or small file.
3. Customizing and changing the Solidworks CAD files.
      - Solidworks 2012 or 2013 CAD software.  
4. Changing the bracelet size and number of rings.
      - Solidworks 2012 or 2013 CAD software.
5. Changing the height of the rings.
      - Solidworks 2012 or 2013 CAD software.

Info about the concept and design, for those who are interested (Warning: technical terms ahead):
Over the last few months I've been playing around with several 'print-in-place' assembly designs because I think the potential for making pre-assembled products on 3D printers is very inspiring. I'd seen some interesting linearly telescoping concentric tube designs that were printed pre-assembled, which got me thinking that it would be neat to play with other geometries and non-linear telescoping (spheres, discs, etc). After modeling some helical telescoping tubes (similar to the kind found in cameras) the idea of an expanding bracelet came to mind pretty quickly. It took a good number of design and prototype iterations to dial in the features of the bracelet while keeping it as aesthetically pleasing and thin as possible, and the end product turned out to be better than I thought it would be. There are a few aspects of the design that worked out to be pretty nice:
1. If correctly fitted as described in this Instructable the bracelet is constantly subjected to a small, outward hoop stress that acts to keep the rings in place nicely when in the expanded position. This was one of those nice unexpected consequences that happen from time to time. I was originally thinking of adding some tiny bump-lock features within the slide-grooves  to keep the bracelet gently locked in the expanded position, but it turned out not to need them.
2. The four rings that make up the bracelet are radially self-contained when rotated, since the cutouts only need to be large enough to fit a wrist.
3. The helical slide-grooves are hidden on the inside surfaces of the bracelet, and the bosses that slide within the grooves are naturally kept hidden within the grooves. This makes for a completely feature-less outer surface of the cylinders and keeps the aesthetic nice.
4. After doing some web searching it appears that no other bracelets like this one exist, at least not that I could find.

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Candrjeski1 year ago
I would love to buy one here's my email please email me. I would love to talk more about this and pricing on it. This is really awesome!!!


Connor Andrjeski
I will buy one too!!
EricYoung (author)  Candrjeski1 year ago
Thanks Connor, If I end up selling them I will let you know.
I'm seeing a nice way to organize all the wires behind my computer. Perhaps even to contain my climbing rope. Great concept.
stricnin1 year ago
OK DC Comic fans. I smell a Wonder Women movie prop. Or Captain Marvel !!!!
annie.jk1 year ago
Can I have a pink one please?
EricYoung (author)  annie.jk1 year ago
If I end up selling them I'll try to make them in pink.
juanjinjo1 year ago
god job brother!!
EricYoung (author)  juanjinjo1 year ago
thanks :)
tinpusher1 year ago
Very cool. Does it rip arm hair out when you take it off?
EricYoung (author)  tinpusher1 year ago
As someone with an abundance of arm hair I can say with confidence that it does not.
PAWZ1 year ago
You must sell these! I totally wanted one as soon as I saw it, even more so after seeing the cool action in the video.
EricYoung (author)  PAWZ1 year ago
Thanks :) I'm considering putting it on Shapeways or Kickstarter so people can buy them if they don't own a 3D printer.
Please do! I would definitely be happy to buy them from Shapeways.
M3G1 year ago
EricYoung (author)  M3G1 year ago
EricYoung (author) 1 year ago
Wow, thanks :) If you end up making any I'd love to see them so shoot me a link or photo if you're up to it.
buell331 year ago
This is a wonderful idea! Looking at especially the white one (but any color could be worked with just the same) My brain is literally spewing out all sorts of girl and guy grunge design ideas for these as well as more girly designs away from grunge and even like boy surf designs. I could totally amp these up! Great idea! Love it!