A captive part is a piece of hardware that is embedded or attached to another such that it's "trapped" inside. This is particularly useful in applications where you want to mount something like a tensioning nut or a leadscrew nut for linear motion. This can also be used to integrate other components, such as electronics or magnets.
In this Instructable I will be going over the basic design considerations required when creating a design that includes a captive part, as well as a tutorial on making a basic flange part with a captive nut embedded. All the software used is either free or open source, and parts files for the flange, the flange with cavity, and the finished STL file for the flange with cavity are downloadable at the bottom of this step.
Fusion 360 (CAD Modeling)
Repetier (3D Printer Controller)
3/8" x 6" Bolt
Prusa i3 3D Printer
In order to create a captive part, we're going to create a pocket in the middle of the larger part for the smaller part to be sit in.
But how will we get it in there, you ask? It's quite simple, actually. We pause the print midway through, insert the part to be embedded, and let the printer continue printing on top of it. No ship-in-a-bottle magic required!
While a variety of components can be embedded, it is important to consider how they will be oriented. Flat objects are generally easiest, as the print head must be able to clear the top of the embedded part. This should also be taken into consideration when orienting the larger part itself.
Minimizing the height of the embedded part in the Z-axis while creating your larger part in a way conducive to 3D printing is a skill that will take some practice. That said, once you have the skill mastered, the time invested into an intelligent design will prevent the need for multiple parts, complex creations, or adhesives.