Sonia Verdu is our Designer of the month for July! Sonia’s design skills are varied but she particularly enjoys creating articulated models with ball joints. Here she’ll go over considerations when designing articulated models so you can try creating your own.
Before I had a 3D printer, I would make my models by hand. I was especially interested in figures that used balls or spheres to articulate. These are typically known as BJDs or Ball Jointed Dolls and offer a great deal of freedom of movement.
The joints are pretty simple; a spherical shape rotates in some sort of cavity. You just need some way to connect the individual parts. I like to use elastic cord because you can get just the right amount of force and have models that will articulate and stay in position. This is how I did a number of my designs like “braq” the dragon, Robotica, and my Jointed Robot.
With 3D printing, instead of manually creating the models we can go a bit further. Joints can be printed in their cavities without any sort of post-assembly required. This makes printing a little more challenging, but it’s well worth it for the final result. Besides, seeing the failed prints is always at least entertaining. I’ll go over the main things you need to consider when making articulated models.
Top Considerations when 3D Designing Articulated Models
Tolerance refers to the distance between two objects before they fuse together. You can learn more about the tolerances of your printer with this calibration file. This will show you how close objects can be before they fuse together. In my case, a distance of 0.4mm between objects looks good. During printing, this tolerance can change a bit with overhangs and defects so to play it safe, I’ll be using a distance of 0.7mm for pieces that I want to be separated while printing.
When people think of thickness in relation to 3D printing, they usually think about layer height which ranges anywhere from 50-300 microns. A more important factor with articulated models is extrusion width which is the minimum width of an extruded line of plastic. Most 3D printer nozzles are 0.4mm which usually correlates with a 0.48mm extrusion width. Check your slicer to figure out your precise value and make sure not to model things smaller than your extrusion width as they won’t print. It’s also useful to model things as a multiple of your extrusion width. For instance you might make a wall 0.96mm rather than 1mm so your printer can precisely match your design.
Maximum overhang angle
Most printers can safely accommodate overhang angles of 45 degrees. Anything steeper than this, requires support structures to prevent layers from sagging. I like to manually design the support structures so that they can be precisely placed and easily snapped away allowing the joint to move. One of my main goals, is to create objects that don’t require support structures to be generated by your slicer to print.
I designed a simple model with one joint. This design works similarly to a Ball Jointed Doll but no elastic cord is needed to attach the pieces together as they print in place. I added two small snap away structures to support the top of the head. They break off after printing and allow for smooth movement.
Your model is ready to be printed! Have a go at making your own articulated pieces. You can use this to hang from glasses and steep tea or whatever you’re in to.
Download this design and many more on Sonia’s profile!
Authour: Sonia Verdu
Since I was a child, I’ve loved painting and 3D modelling so I decided to study Art at Complutense University in Madrid. At the same time, I was studying ceramic modelling and spent my days covered in clay. For several years now, I’ve worked as a designer and illustrator and have had a few paintings commissioned.