How to Design Moving Parts in SketchUp for 3D Printing

By Aidan Chopra, Rebecca Huehls

3D printing something you’ve designed in SketchUp is cool. 3D printing something that moves is even cooler. This info focuses on a few features you can include to make your creations more than just interestingly shaped hunks of immobile plastic.

Captive joints in SketchUp

A captive joint is a moveable connection that comes out of your 3D printer already assembled and working. Captive joints tend to be mechanically simple hinges, ball joints, and chain links. Their simplicity is their power. A 3D printer can quickly build objects with hundreds of captive joints that would take days to construct by hand. Poseable action figures, clothing, and the chainmail are examples of simple captive joints assembled into complex structures.

captive joints SketchUp
Captive joints bring the power of multiplication to life.

Creating a captive joint requires trial and error. You’ll have to experiment to get the right combination of clearances and shapes. Keep these principles in mind while you work on captive joints:

  • Use components when building structures with captive joints; they let you automatically modify all the joints at once as you work.
  • How you design captive joints depends on the specific 3D printing technology you’re using. SLS-based 3D printers can build captive joints that are a few millimeters across. FDM printers can make fantastically strong joints, but the printed objects need to be much bigger.
  • A structure is only as strong as its weakest part. Don’t make a joint so fine that it falls apart in your hands.
  • Test print parts of your structure as you work. Remember, 3D printing is cheap, and with captive joints, you’re pushing the limits of the technology. Test objects will help you check your work and keep your sanity.

SketchUp Pins

Pins are small, round snap fittings that are pressed into place to make a connection. They can be a versatile replacement for hardware. Here, a single pin acts as a point of rotation, and two or more will hold parts firmly together.

SketchUp Pins
A system of pin joints used to make a simple toy.

Pins are like bolts, except you get to make them in exactly the size and shape you need. You can also print more when you run out.

  • When designing your pins, give them one flat side. The flat side gives you a way to build the pins without using support material — while keeping the tongues horizontal to the build platform. This process also keeps finished pins from rolling off your desk.
  • Make your pins into components so you can easily modify all of them at once if you need to.
  • When designing a project with pin joints, make an effort to standardize around a small number of pin sizes. Standardization helps keep things tidy and simplifies assembly.

Gears in SketchUp

Gears are great for creating complex motions or transferring movement through a mechanism. That is probably the most understated description of the deepest rabbit hole of the industrial age. Gears are in every mechanical device you can imagine. They have existed in some form or other since before recorded history, and are the basis for an incalculable number of clever devices that make everyday life possible.

Making gears is fun and inspires lots of folks to start experimenting with 3D printing. The image below shows a simple gear system that can become so much more. To help you get started, here a few basic principles for making gears:

  • Gears need to have clearance between their surfaces to work properly. Gears that are too perfect a fit will bind up. Include a clearance at both the point of rotation and between the teeth of the gear and the teeth of its mate.
  • A SketchUp extension called Involute Gears automates the process of making gears. The extension’s creator hasn’t made it available in the SketchUp Extension Warehouse, so you’ll need to locate it by searching sketchup gear plugin through Google.
  • Creating optimized gears from scratch is a technical art form that has fallen out of practice. If you want to learn more about designing gears, get a a copy of Machinery’s Handbook (Industrial Press). After almost a century in print, this book is the gold standard for anything gear-related.
sketchup gears
Welcome to the New Industrial Revolution. Time to gear up.