I am often responsible for rapid prototyping parts on the job as a mechanical engineer. Regularly my designs require the use of captured nuts to joint parts together. It is possible to add a pause in your 3D print and embed nuts, but often my prints last days and run when I am not around to place nuts in the print.

In this Instuctable I will show you my technique for creating captured nuts of any size that can be placed and strongly retained after the print is complete. I have used many sizes of these in fixtures that have been through 10,000 cycles of fatigue testing at 800g's without failure or loosening. While this isn't a revolutionary idea, I have scientific testing behind the sizing of these captured nuts. I hope I can save you time, teach you a CAD trick, or inspire you to come up with a better way to hold onto your nuts!

Required Materials:

  • Vernier calipers.
  • Nuts and bolts (I am using M6 in this example).
  • 3D printer or 3D printing service such as 3DHubs and through Instructables.
  • CAD (Computer Aided Design) software capable of saving .stl files. I am using Solidworks 2015.
  • Hammer.
  • Punch or screwdriver for driving nuts into holes.

Special Note:

Your 3D printer must be well calibrated dimensionally or you will need to adjust my numbers to suit your printer.

Two styles of captures

I will show you my two different styles for capturing the nuts. I call the first style "pocket style" as a hexagonal pocket is used to hold the nut. The pocket style is shown as the left part in the intro picture. As you will see this style captures the nut using detents (little bumps) in the corners of the pocket. This style works great in tension (pulling parts together) and is easiest to install the nuts. A downside is that you must have access on your part to the outer face of the pocket.

The second type is "slot style" as the right part in the intro picture illustrates. The nut in this design is retained by one detent resembling a speed bump. This style works in both tension and compression (pulling parts together and pushing them apart) and is great for hard to reach locations. You can make the slot as long as you need to reach your bolt hole location. The downside is it is a little tougher to install the nut.

Step 1: Measure Your Nuts and Bolts.

To begin you must measure the width and thickness of your nut. Also measure the diameter of your bolt. Write these values down. As previously stated I am using an M6 bolt with M6 nylock nut. The nut measures 0.389 in (9.88 mm) wide by 0.2275 in (5.78 mm) thick. The diameter of the bolt is 0.231 in (5.87 mm).

For slot style captured nuts you will also need to measure the point to point maximum width of the nut as shown in the 4th picture. My M6 nut is 0.4375 in (11.11 mm) wide from point to point.

<p>Don't forget to vote for my project in the 3D printing contest! I could use a good home printer for sure!</p>
To drive the nut in your first example just screw the nut onto a bolt and hammer on the end of the bolt. You won't damage the threads and it's easy to align it all three axis. Since my printer is not that accurate I usually push the nut in place with a hot soldering iron. This would be tricky with a nylock though.
<p>This is good stuff to keep in mind.</p><p>Different nut styles might come in handy too.</p><p>Barrel nuts</p><p>Square nuts</p><p>Tee Nuts</p>
<p>dont understand this entry. the sells mendel files done this, like 5 years ago</p>
<p>This is not a patent application. There is no requirement for originality. It's a nicely written instructable that will surely inspire others.</p>
I'm sure he didn't mean to steal the idea... I mean it WAS 5 years ago. I think it's good to have an instructable like this now, 3D printing has changed over years, ALOT. This is very well put together and thorough, he should be allowed to enter it.
<p>I use an industrial printer at work. I have never taken the time to wade through all the reprap information there is. I searched Instructables and didn't find anything similar or well written. Printing pockets and slots with detents is an obvious solution that I'm sure many have come up with independently. I just wanted to help people out by showing how I model and size them. They can be used by others anywhere they want without having to test their own ideas. I have used both styles of captured nuts in fixturing that has been through over 10,000 cycles of 800g impacts without failure so I know they work. </p><p>So many 3d printing entries in this contest are &quot;print this thing&quot; and aren't about learning but about copying. Other entries are a very specific solution to a very specific problem that not many people have. I thought about this, and while my Instuctable doesn't have the &quot;sexiness&quot; of a 3d printed prosthetic, I'm sure far more people are trying to attach a part to something than trying to make themselves a new arm.</p><p> Maybe someone will see my entry without having thought about making a slot for a nut. Good for them. Maybe someone has been creating new planes in their CAD to make a detent instead of using a face of the nut pocket to save time. Now they know. Maybe someone will see the detents in the corner of the pocket style captured nuts and think that's dumb and decide to glue their nuts in. As other commenters have said: maybe they will melt the nuts in place, maybe they will use the bolt to insert them instead of a hammer, maybe they invented quantum teleportation and don't have to touch the nut at all. It's all good!</p>
<p>Doesn't SolidWorks let you change the vertical axis?</p>
You can change the standard way the part is oriented in the views, but in all my searching (even calling our &quot;value added distributer&quot;) I haven't found a way to change the axis orientation.
<p>Sometimes people start with a round hole, heat up the nut and push it into place. It may result in a tighter stronger fit.</p>
<p>Love it!</p>
<p>This is a typical technique used in the reprap project. It's also a good idea to heat up the nut with a lighter before sliding it in the slot.</p>
<p>I know it is a pretty trivial thing to do. I wanted to share my dimensions and CAD experience to save people the time and material it takes to test detent sizes.</p>
<p>Hi I do something similar but suggest that thumping the nut into place will or could induce stresses which will cause the part to fail either in the short or longer term. It is better to gently press the nut in place using a vice, clamp or press.</p>

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