3D Printed Parts Choose the Best Fasteners for the Fit

We had a lot of questions about the best way to fasten different 3D printed components. For example, when prototyping hardware products, it is often necessary to make assembled structures that are more complex than individual 3D printed components, such as electronic housings or robotic components.

Occasionally, you may need to print components of a build kit that is too large for a 3D printer, so you need to consider ways of assembling the printed parts permanently or intermittently.

One way to assemble 3D parts is to use snap-fit components, but another great way is to use threads.

There are many different ways to implement threading in 3D printed parts, so we’ll cover the pros and cons of the most common methods, as well as specific installation steps to help you get started.

Our preferred method, and the one we most often recommend, is to use a threaded insert because it is easy to install and has a great feel.

Pros: Quick, easy, clean; unlimited assembly/disassembly; production quality

Cons: More expensive; requires increased wall thickness

Materials and Tools: Brass Insert; Soldering Iron; Precision Knife

installation steps:

1. Put the insert into the relevant hole to be pushed in

2. Using a heated soldering iron, place it in the middle of the insert and apply a small amount of pressure.

3. When the insert starts to heat up, you will see it sink into the hole

4. Once the blade appears flush with the surface of the part, use your precision blade to inspect and trim any excess material

An alternative to threaded inserts is to use self-tapping screws. If you want something quick but dirty, this is the easiest and cheapest way to do it, so if this is your first prototype, or you’re working with low-res materials like PLA, self-tapping screws are a great way to Good choice.

Pros: Easy installation; minimal design requirements; inexpensive

Cons: Brittle material may crack; limited assembly/disassembly; low strength; materials and tools; self-tapping screws

installation steps:

1. It’s as simple as a screwdriver and a screw…just one twist
When designing parts that require very large threads, the best approach is to design the threads into the 3D model itself.

Advantages: Custom threads can be designed; good when inserts are not available (i.e. M50 threads); suitable for brittle materials

Cons: Threads wear out over time; Difficult to model accurately; High resolution printing required; Materials and tools

None (CAD only)

Installation Steps
1. Ensure accurate thread modeling

2. Print components using high-resolution materials

3. For internal threads, use a tap to “finish” the thread. If you don’t have taps available, try using machine screws.

4. For male threads, use a steel nut that matches your thread size and use that to finish the thread on the part.

5. Make sure to fully tap the through hole of the part – this will ensure that excess material is removed from the tapped feature and the part is ready for tightening.

6. For blind holes, be sure to tap deep enough to fit, and be sure to clean any excess material (attempting to screw fasteners into parts with debris can damage your function).

When adding threads to a printed part using this method, be sure to maintain vertical alignment with the threaded feature; it is worth taking special care to avoid cross-threading, which can cause permanent damage to the part.
This is the most traditional method of using threads. In subtractive manufacturing, drill taps are used to create the desired threads in each hole once the CNC has placed the holes where the threads will pass.

When prototyping with 3D printing, you can create threads in a plastic prototype using the same method as a hand drill tap.

Advantages: better assembly/disassembly than self-tapping screws;

Cons: Low strength; plastic wire wears over time; time intensive

Materials and tools: drilling and tapping; screws;

installation steps:

1. Tap the thread feature with the appropriate drill bit to cut the available thread

2. When applying torque, be careful not to damage the parts

Fixed hex nut

Another common strategy for fastening parts together is to create printed pockets that capture hex nuts.

Advantages: low cost solution; good holding force; easy to install

Disadvantages: Applies only to outer surface; requires additional material to secure nut; design constraints

Materials and Tools: Hex Nuts; Screws

How to use this method:

1. Measure your fasteners – this is a great resource to help you.

2. Add a little tolerance (0.005 – 0.010 inches) to the hole size to accommodate any dimensional errors.

3. Before pressing the nut into the bag, apply a little glue to the nut, but stick it to the inside surface of the bag. Otherwise, when torque is applied to the nut, it may be pulled out of the groove

Mechanical Notes

The following three questions can help you consider which approach is best for your project:

1. Do you need to disassemble and reassemble components?

2. What is your strength requirement or retention?

3. What are the geometric or spatial constraints inherent in part design?

Additionally, when designing your fastening function, keep in mind the following three important considerations:

1. Bending along an axis parallel to the print should generally be avoided as components printed in this direction are much weaker in structure.

2. When adding assembly features, pay attention to the allowable stress and strain of the material.

3. Before adding fastener features, check the CAD model carefully. For example, if you are adding a hex nut, check the height of the hex nut you are using; if you are using a threaded insert, check the pitch of the installed insert.