A guide to screws for 3D printed parts

3D Fasteners Explained - your questions answered:

There may come a time when the project you’re working on requires that you fasten 3D parts together – but where to begin? ‘Should I print 3D screws – and: ‘if so, which polymer should I use?’ might be just two of your questions, with a third being: ‘Are off-the-shelf threaded screws the answer?’

You’ll know that when prototyping hardware products, you may need to manufacture assembled structures – like an electronics enclosure, for example – which is more complicated than an individual 3D printed component. Or perhaps your project requires that you print components that are too big for the build envelope of a 3D printer.

To help you make an informed decision about all things fasteners, we explore your options by providing the answers to some of your burning questions.

Should I print 3D screws?

If you’d like to create custom-sized threads and ingenious assembly systems, 3D screws may be the way to go. Helping you save money on your project’s costs, you’ll find that you can create the exact assembly system you need.

However, if you’re planning to 3D print screws you can find online, 3D printing isn’t always the most cost-effective option.

Which polymer should I use?

It can be a challenge to select the right material to print a specific object. This is due to the 3D printing market’s ongoing development of revolutionary, new materials. While Poly(lactic) Acid (PLA) and Acrylonitrile Butadiene Styrene (ABS) are often the two key polymers used, new products – like pure polymer and composites – are now sliding into view.

Poly(lactic) Acid (PLA), Polyethylene Terephthalate (PET), Acrylonitrile Butadiene Styrene (ABS), Thermoplastic polyurethane (Flexible), abbreviated to TPU; Nylon, and Polycarbonates (PC) are the main polymers on the market today, each of which are suitable for a different application.

The simplest polymer to print, Poly(lactic) Acid (PLA), gives good visual quality and is strong but brittle. Polyethylene Terephthalate (PET), meanwhile, is a well-rounded, softer polymer. With few downsides, it has high humidity resistance, and is recyclable.

Moving onto Acrylonitrile Butadiene Styrene (ABS), which is often selected in place of Poly(lactic) Acid (PLA), when higher temperature resistance and strength is key. Predominantly used for flexible applications, TPU provides high-impact resistance as well. Nylon, on the other hand, offers excellent mechanical properties and, for a non-flexible filament, provides high impact resistance.

Finally, Polycarbonates (PC) – the strongest of the polymers – is a good alternative to ABS but offers similar properties. It can also be sterilised, as well as proving simple to post-process.

What about off-the-shelf, threaded screws?

There’s a lot online which suggests self-threading screws are the way to go, with someone posting the following via RepRap site – a site responsible for ‘humanity's first general-purpose self-replicating manufacturing machine’.

“For holding stuff together self threading screws are way more useful than printed ones.”

Another site visitor confirms self-threading screws’ benefits, adding: “Yeah, I'm sure off-the-shelf (metal) bolts are much better quality - but I’m designing components that, if they were to require standard hardware, would require hours of complicated assembly. And I need to make hundreds of them...”

It would seem, then, providing you are working on a relatively small job which requires few components, self-threading screws are most definitely the answer.

How do I assemble 3D printed parts with threaded fasteners?

First, keep in mind that the minimal wall thickness surrounding a thread should be the same thickness of the fastener itself. If, however, wall thickness is too low, parts can move and distort. This is due to the extra stress and it’s worth noting that, in some cases, fracture or delamination may result.

Inserts, embedded nuts, cutting threads, self-tapping screws, or printing threads are the key methods for assembling 3D printed parts with threaded fasteners. Below, we look at the self-tapping method.

Cutting a thread into a pre-drilled hole as they’re screwed down, self-tapping screws ensures a quick assembly method. That said, it is not suitable for applications where parts will regularly be taken apart and put back together.

Here’s what to do if you’re using the self-tapping method:

• Begin by 3D printing or drilling a hole into the chosen location of your screw. To ensure you select the right pilot hole, take a look at the self-tapping screw provider for some instructions. As a general rule of thumb, a hole that provides around 75 to 80% thread engagement is a good place to start
• Now, assemble the components you need to secure. Ensure that you correctly align the holes where the self-tapping screws will be required

Finally, slowly screw the self-tapping screw into the hole. You should make sure that it stays perpendicular to the hole as it is fastening.