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Three Ways to Add Threads to a 3D Printed Part

By David Ramsey on December 17, 2021

The idea for this tip came to me as I was working on my remote-control (RC) Ornithopter design. The goal is to securely fasten the flap mechanism for flight and at the same time, a way for me to disassemble when needed. There are a few methods I can use to add threads to this 3D printed part, and in this article, I will add threads using the best method for this application. Glue is an excellent lightweight and strong option, however, I wanted to be able to disassemble my bird. So glue won’t cut it. I needed a better solution. For me, that means incorporating set screws and threads into my design. Let’s look at three methods typically used to add threads to 3D parts and why I chose one method over the others.

Direct Printing Threads into 3D Part

Printing threads in a 3D printed part

Directly printing threads have merit because no secondary operation is needed to produce a threaded part. But there are limitations with this method. Thread quality (visually and mechanically) varies with the orientation of the print. The size of the thread must also work within the resolution capabilities of the printer being used. The sample block shown below has Both M2 and M20 threads printed in the horizontal and vertical orientations to showcase the difference in printer capability. I need to use an M2 size set screw. As you can see, I can’t print the threads directly into the print because it’s not in the printer’s capabilities to print threads in this size. Note that different 3D printing technology, such as PolyJet and P3, have better capabilities at printing threads than FDM technology.

Heat-Set Threaded Inserts

Adding heat inserts to a 3D printed partSo, what about heat-set threaded inserts? These are great for strength and thread consistency. They can even be added to fused deposition modeling (FDM) prints in a similar fashion to traditional over-molding. This scenario provides the best case for strength but also has its share of drawbacks. Threaded inserts aren’t readily available in every size, and when working on lightweight projects like this one, the weight of the inserts is a deal-breaker.

Drilling and Tapping

Add threads to a 3D printed partThe best solution is going to be drilling and tapping. Since my design is small and keeping it as lightweight as possible is crucial, manually threading this part was my best option. By using GrabCAD Print to prepare my part for printing, I was able to set the holes to be self-supporting, which means that it won’t use any support material when building the holes in the model during printing. Once the print was complete, I was able to tap into the self-aligning, diamond-shaped hole and run a tap to create threads. Now I have a functioning flap mechanism that is secure and removable, and one step closer to getting this bird in the air.

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