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Written by Ben Redwood
Threaded fasteners are a popular method of securing 3D printed parts. Threaded fasteners allow quick assembly and disassembly and offer strong connections.
This article will discuss the most appropriate threaded fastening techniques to apply when dealing with 3D printed parts and discuss the methodology behind implementing each of them.
Read next: The practical engineer's guide to thread types →
As a rule of thumb the minimum wall thickness around a thread should match the diameter of the fastener (e.g. an M5 fastener requires a minimum of 5mm wall thickness around the threaded hole). If wall thickness is too low parts can bulge and distort due to the added stress and in some cases (particularly FDM) delamination or fracture can occur.
The table below introduces the threaded fastening methods that are best suited to 3D printing.
Process | Description |
---|---|
Inserts | Popular method used regularly that gives a strong metal on metal connection but requires additional components and installation |
Embedded nut | Fast method for securing components. Accurate design and print are needed |
Self tapping screws | One off method of securing parts that is not suited to repeated disassembly |
Cutting threads | Cutting a thread offers design freedom however correct tapping procedure is important |
Printing threads | Not suited for small threads (less than M5) and requires high printer detail/resolution to print accurately |
Note: Drilling the pilot/alignment hole to the desired diameter post-printing, before implementing any of the fastening methods discussed in this article, will typically give a more accurate diameter compared to a 3D printed hole.
Two types of inserts are best suited for 3D printed parts; heat set inserts and tap-in inserts. Inserts provide strong metal on metal contact and are very easy to install. An accurate pilot hole is required so drilling is recommended before installation.
Heat set inserts
Tap in inserts
Another method of securing 3D printed components together is to embed a nut into the component via a nut shaped cavity (often referred to as a nut boss). This method does not require any material removal. Often determining the optimal nut boss dimensions requires several iterations. Printing small test parts to determine the ideal dimensions can save on time and material costs.
Self tapping screws cut a thread into a pre-drilled hole as they are screwed down. This offers a quick assembly method but is not suited for applications where parts will regularly be assembled/disassembled. Special self tapping screws for plastic can be used that limit the radial stress on 3D printed holes lowering the likelihood of bulging, delamination or fracturing occurring.
Cutting a thread (more commonly known as tapping) involves using a tap wrench to cut a thread in a pre-printed or drilled hole. Threads are regularly cut in 3D printed plastics.
3D printing threads eliminates the need for any extra steps post printing and allow parts to quickly be assembled together. Limitations on printer accuracy and resolution will govern the success of a printed thread. Threads smaller than M5 printed via FDM should be avoided with one of the other threaded fastener methods discussed in this article implemented instead.
After printing the threaded fastener should be screwed and removed from the hole several times to clean the printed thread before final assembly.
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