Threads are a reliable & proven way of attaching components together by bolts or screws. In 3D printing, particularly with Multi Jet Fusion (MJF) and Fused Deposition Modelling (FDM), there are several methods to incorporate threads into parts, each with its advantages and limitations.
Tapping the Hole
For Multi Jet Fusion the official design guide from HP favours tapped holes. The process is very similar to tapping a hole into a block of plastic. Design your part with the correct hole size before they are tapped.
For MJF parts, this method works well but with some caveats:
Design Considerations: Ensure the hole is designed with the correct diameter before tapping.
Limitations: Small threads can be fragile, and plastic threads can be easily damaged if bolts are frequently removed.
For FDM we would avoid this method unless there are no other options.
Using Brass Threaded Inserts
Brass threaded inserts, especially heat staked inserts, are highly recommended for their strength and durability.
Best Use: Suitable for small threads (M1.5 - M6), which are fragile if cut directly into MJF parts.
Advantages: More robust than plastic threads, less prone to cross-threading and wear.
Design Requirements: Design holes to match the insert manufacturer's recommendations. Ensure proper boss size to accommodate the inserts. Don't forget to check the boss dimensions, a mistake we often see.
This method is also suitable for FDM parts!
Printed Threads
Integrating threads directly into the CAD design can be done but is rarely the best solution.
Challenges: The fine details of threads may not print accurately due to the minimum feature size limits of MJF. This can result in rounded and imprecise threads.
When to Use: Suitable for large or coarse threads, where precision is less critical.
The problem with printed threads becomes apparent when looking at a cross section of the thread:
This image compares an M10x1.0 with an M10x1.5 thread. As you can see the thickness of each tooth of the thread feathers down to a very thin edge. On the M10x1.0 this goes all the way down to 0.13mm, which is significantly below the minimum feature size for our 3D Printing Services. In this case the thread will probably print, but it wont be very accurate.
Conclusion
The best method for adding threads to 3D printed parts depends on the application and thread size. Generally, for small and frequently used threads, brass threaded inserts are preferred. For larger threads, tapping them into the part is a great option. Generally we advise avoiding printed threads unless accuracy is less important.
For optimal results, parts should be reviewed and designed according to the specific needs and limitations of the 3D printing method used. If you need assistance, our team can provide recommendations tailored to your parts and intended use.
