Introduction: 3D Printed Twisty Bracelet
This was inspired by https://www.instructables.com/id/3D-Printed-Spiral-Earrings/ the design closely follows a similar principle.
The design provided easily slides onto most sizes of hands, but anyone can manipulate its dimensions easily in Makerware or GCode. It has a slight stretch to it, and fits comfortably on wrist because of its relaxed design structure.
You can download the stl file at:
Step 1: CAD Design
My program of choice is Autodesk Inventor, because it is available for a free 3 year trial as a student, and also because it makes constructing these more complex designs easier compared to 123 Design available from autodesk for free download (a more rudimentary version of Autodesk Inventor)
The design primarily uses a lofted feature (looks like an C) which is mirrored and then copied around in a circular pattern to create the bracelet shape.
You can see in picture 2 that i have made 7 different sketches placed 4 cm apart each to construct this design, after the sketches are finished with each hole being 3-4 mm thick i used the loft tool to create a 3D part. Make sure you ease your workload by using the mirror and project geometry tool. The pattern the sketches have to follow can be seen in pictures 3 and 4. The lengths and sizes do not have to be exact and in my case i made the curve of the C more shallow by shortening each circles distance away from the center.
Step 2: Links
The steps get simpler from here, basically you want to "mirror" what you did so you have a chain link, and instead of using the mirror tool i made an axis in the center of the design and used the circular pattern tool, set the pattern amount to 1 and finished the process, your link should look something like this.
Step 3: Final CAD Step
So the simplicity and ease, of 2nd and 3rd step just go to show the many iterations you can make of this sort of design so i really want to see what others on instructables will make.
The next thing you want to do is create a circular pattern around the size of circle which you intent to use.
To determine this i simply took a measurement of the length from one side of my hand to the other at its widest point with a caliper.
In inventor i created a circle which has a radius of half the length i measured + 10 mm's for shrink and fitting compensation.
(in my case 45 mm)
So after finding the proper size and placement for the circle that i wanted the design to follow i extruded it (not the best way to go about this but faster ) then placed an axis marker, deleted the entire extrusion with out the work features tied to it, and made a circular pattern around that axis. I played around with the amount of features added in the pattern until i found a number setting of 12 where the designs interlocked with each other and touched. You want to make sure you have each link touching because the rigid structure will maintain its integrity better and also with designs like this it would turn into a weird chain like structure.
Step 4: MAKERWARE
For some reason when ever you export stl files from inventor it scales them down by a factor of 1/10.
To compensate for this in makerware you have to scale up by 1000%.
Your design for some reason may also not turned correctly, you should be able to adjust this by increments of 90 degrees with the rotate tool in makerware.
Finally you should make sure your design is on the build platform.
I printed mine with a 1 percent infill and 1 shell with rafts.
if i were to print this again i would use 2-3 shells for better strength, although i have not had too many problems with it breaking because of its flexible nature. (printed in ABS)