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.

Software used:

Fusion 360 (CAD Modeling)

Repetier (3D Printer Controller)

Hardware used:

3/8" Nut

3/8" x 6" Bolt

Prusa i3 3D Printer

Step 1: Design Considerations

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.

This is such a simple but fantastic idea! Will be using this for sure!
<p>I always do it this way :)</p>
Nice work on the step-by-step. <br>Out of curiosity, as a traditional machinist with no real 3D printing experience, what is the purpose for the nut; embedded or otherwise? <br><br>If the part design requires internal threading why not bore the two holes to depth then cut the threads in the part itself? Or insert the nut from the end and capture it with a circlip? Variations are endless. <br><br>I'm not taking a swipe at your design or execution, I'm genuinely curious. Thanks!<br>
<p>The other reason I love captive parts is durability -- I made a shuttle platform for my camera (so you can turn a threaded rod to move it), and I'm not worried about the threads wearing out fast (despite it running all over the place) because I embedded a self-lubricating-bronze nut inside the sled. If I had put the threads in plastic, I think it might've lasted 100-200 cycles, but this showed no signs of wear before the project was finished.<br><br>So I always make my threads an embedded nut (a steel nut works much better on my tripod than the plastic) instead of trying to tap them -- just so easy (as long as you put a &quot;pause&quot; in the workflow... otherwise, you gotta watch it)...</p>
<p>Similair to what askjerry was saying, there's a couple reasons.</p><p>One of the coolest to me is the fact that it's just not something you can do on a mill or lathe - only with additive machining can you have truly captive parts. And that's really cool to me.</p><p>Another option is the fact that this can extend to more than just nuts - you can embed electronic components in a very similar way.</p><p>And another consideration to keep in mind with regards to nuts is strength. Tapping directly into 3D printed plastic might not work so well - a lot of times 3D printers don't fill in the entire part, just the outside frame and a lattice on the inside (see towards the final step where you see the grid pattern in the half-printed part). This saves in both filament and weight. Tapping into the &quot;hollow&quot; part might not give the results you want. Even with a solid print, the threads might not hold up to well against any reasonably load.</p>
Does a turners cube count as captive? <br><br>I'm glad I asked. I did not know some 3D printers leave pockets in the parts. The tiny spools of filament I've seen make a lot more sense now. Just by eyeballing the spools I thought there wasn't a lot of material to use.<br><br>Thanks for the info!
<p>I certainly consider a turners cube to be a captive part.</p><p>And here's a good diagram showing what the infill looks like:</p><p>http://img13.deviantart.net/558d/i/2014/041/a/4/3d_printing_infill_by_triplaxis-d75wmax.jpg</p>
<p>One reason would be the material used... some filament is flexible like rubber... it would never take a tap. You may still want to secure it tight, to make a seal or something. This way you could install nuts at regular intervals, and without the possibility of loosing them. Possibly in a hostile environment, to protect them from rusting for example. It also opened the door for other things, like embedding a circuit board, an LED, a switch, a magnet for sensing, etc. I could see this method being very useful.</p>
Thank you so much for posting this Instructable. I'm so very new to the 3D printing world and I've been thinking there has got to be a way to do this, but I wasn't sure until now. As soon as my new nozzle comes in, I'm definitely going to be trying this!
Definitely! I'd love to see how it works for you, you should post the results! <br><br>Feel free to shoot me a PM if you run into any problems.
I will definitely try to remember to do that. what I'd also like to learn is how to print treading for bolts and screws. It would be nice to make my own hardware for specific light duty needs.
<p>Printing actual threads that properly mate can be a bit tricky, mainly due to support and sagging issues.</p><p>Modeling the threads isn't too tricky. If you'd like I can whip up a quick little guide on how to do it in Fusion 360. </p><p>I've seen people print good threaded items, but I've never had too much success. Let me know how it turns out though, especially if you find a way to make them come out well!</p>
I just recently got my hands on Fusion 360(a student copy) and was just playing around with the threading and holes. Fusion is a bit different than the 123d I have been using, but I like the extra functionality. my part should be coming from China any day now as I ordered it almost a month ago. I'm definitely going to play around with it and see what I can come up with. I didn't see the threading that I was looking for, though and that makes me a little sad. I was hoping to find a 1/4-20 thread, but only saw 1/4-14. I suppose the coarser thread would be better, but it would be nice to have the extra option. <br><br>I've been in touch with a gal from autodesk and she's been feeding me tutorials, but I haven't spent a lot of time playing around with it yet. I should be able to figure everything out for it though. Like everything else, it just takes a bit of patience and time.
Nice instructable! To see an example that I did, check the pic on my 3dHubs page: www.3dhubs.com/Toronto/hubs/jsfieldtech
<p>Thank you! This gives me some new possibilities, which I haven't thought about yet. In case someone is using Cura from Ultimaker 2.3+, the pause setting will be found here: </p><p>Go to Extensions/Post Processing/Add a script and you will find the &quot;pause at height&quot; script</p>
Thanks for the heads up! All I've used so far is Cura and I enjoy it. I was hoping I wouldn't have to learn a bunch of new software.
<p>Definitely. I was never able to get the Cura plugin to work to my satisfaction, which is one of the reasons I switched over to Repetier. To each their own, though!</p>
<p>I've done a few of these myself. It is a great way to include durable threads into a plastic part. I have also used the same technique to make refrigerator magnets from HD magnets. The tricky part with magnets is they will stick to the gantry shafts on the printer so I had to superglue them in to finish the piece.</p>
<p>excellent work this is very good </p>
<p>That's very cool, I'll have to look in my software to see if mine includes that option. I'm just starting in 3D printing, and I don't even know what I don't know yet :) </p>
<p>The wonderful thing about hobbyist 3D printing is that there's so many free and very well made choices for software, so everyone can find something that works for them. If you have any questions, feel free to drop me a PM and I'll do the best I can to help!</p>
<p>Thank you! </p>
<p>Very nicely done, great instructions!</p>
<p>Thank you! It's something I found was really cool, and I hope that others will think it's as neat as I do.</p>
Very interesting! Do you print on the top side of the nut or is there a gap? I could see using this as floating hardware which solves some of the tolerance issues of 3D printing.
<p>You can do either, it's up to you. If you leave a gap you might have some bridging issues, but the nut will ultimately provide support. One thing to keep in mind is that the print head must <em>absolutely</em> clear the nut, so if you don't design the pocket deep enough you might have a crash.</p>

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