How to Thread Your 3D Printed Parts

2024/ 12/ 12 ,Chloe Vollaro

Image source：Formlabs

Should you stop hand-tapping threads into your 3D printed parts and design threads instead? It depends on the thread.

Certainly, industrial 3D printing technologies have the accuracy and ability to 3D print threads into parts exactly where they’re needed, so why do so many companies send their metal and polymer parts to the machine shop?

We, here at Protolabs, get a lot of questions about the best way to add threaded features to the CAD models for 3D printed parts. This is no surprise since additive manufacturing technologies are increasingly being used for both prototypes and end-use production parts.

Aerospace and defence contractor Figure Engineering 3D printed this threaded part that will act as a mask for this large bolt during electroplating. Printed on a Formlabs Figure 4 resin 3D printer (Source: Formlabs)

The most important thing to know is that the success of as-printed threads (those that are created during the printing process) will vary greatly depending on the printing technology and thread size.

Every 3D printing technology has a minimum feature size (along with unique print settings and finishing methods) and this also varies depending on the exact brand of 3D printer. We’ve seen threads fail to engage well or not print at all if they are not properly designed for 3D printing and the specific process. This is due to the fact that threads with tapered edges will lose material once they get thinner than the minimum feature size for the selected material and technology.

When designing parts that need threads, you can’t just rely on the thread generation function in your design software like, Autodesk’s Fusion; there are more factors to take into consideration.

For example, for parts that have a rougher surface right from the machine—such as those manufactured using selective laser sintering (SLS) or metal laser powder bed fusion (LPBF) — the surface roughness can actually impede thread function. But all is not lost! There are several ways you can get functional threads on your printed parts

Although we tend to not recommend as-printed threads for many parts, there are some solid methods we — and other manufacturers — recommend to solve tricky treading situations.

Adding Threads to Plastic Printed Parts

UK-based 3D printing service 3D People, says the metal threads of a heat-set insert are more durable than their plastic counterparts (Source: 3D People)

If you’re looking to 3D print a very basic, large thread on a 3D printed screw-top container for example, check out the “3D Printing Threads & Screws – Simple Guide.”

In this article, we cover your options for professional and industrial applications. When it comes to polymer parts, such as a carbon-fiber nylon GoPro mount, you have some thread options.

The first option is to print the part without threads and tap the treads in afterwards. Tapping is the process of creating threads inside of a hole for a screw or bolt with a “tap” or “thread cutter” that looks like a drill bit. It essentially carves the exact thread design into the inside of the hole as it advances. This is an option for parts that need to be screwed together once and left that way. Continuously inserting and removing screws could wear down the thread.

If your existing CAD model includes threads, remove them and size the holes slightly smaller than the drill size corresponding to the tap for the threads you want to cut. Standard tap and drill size charts for machining, which you can find online or in an app, will also apply to 3D printed parts. For the bes results, ream the hole prior to coming in with a hand tap.

Self-tapping screws, also called thread-forming screws, are inserted into a negative feature with no preparation work done to the part. Follow the manufacturer’s guidelines for hole dimensions. These are a good option for 3D printed parts made from a polymer with a bit of elasticity, like nylon.

If you need a stronger thread, brass or steel inserts are your best bet. These some in a variety of styles.

Heat-set inserts (also called heat-stake inserts) are installed using a soldering iron which heats the insert and the plastic around it. The insert is pressed into the softened plastic until it is flush with the surrounding surface.

For stereolithography (SLA) or any type of resin printing, the best option is screw-to-expand inserts because these resin materials are affected by high heat.

Screw-to-expand inserts used on a continuous carbon fiber nylon part 3D printed by Markforged (Source: Markforged)

All inserts should be removed from the file when uploaded to the printer so they aren’t accidentally built merged with the part.

A key design consideration for tapped threads and heat-set threads is the ability to access the holes. If the hole is blocked by other features that prevent threading tools from getting to it, there’s no way to thread or install inserts.

When it comes to inserts, there are a few more things to think about. The diameter of a given insert is always bigger than the diameter of the thread. You want to make sure there is plenty of room around the hole so that the insert doesn’t break through the surrounding wall.

For SLS and MJF, consider the geometry surrounding the hole receiving the insert. Typically, inserts aren’t pressed in perfectly straight, so a soldering iron may be used to adjust the alignment after they’re pressed into the part. Because of the heat and maneuvering to ensure they’re properly aligned, you want plenty of room between the insert and adjacent features so that nothing gets melted accidentally in the process.

In a perfect world, you’d add 0.25 in (6.35 mm) of space around an insert if it is surrounded by features on all sides. However, if the insert is near a wall, but otherwise has no nearby features, the wall can be a bit closer because there is plenty of space in all other directions to install the insert without risking damage to the wall.

If you’re ordering your parts at a 3D printing service, inform the manufacturer that you want tapped holes or inserts and not include them in the model. Instead, include a formal drawing, quick markup, or a screenshot. Indicate thread size and location. If the manufacturer is threading thru-holes, let them know the direction in which they should tap or install the inserts. By default, most manufacturers install inserts flush with the surrounding surface, but they can be sub-flush, if needed.

Another option is to design your part to accommodate a standard steel nut. For this, you would directly print a nut holder or a pocket for the corresponding nut.

US-based 3D printing service DI Labs used Multi Jet Fusion technology to print these valve bodies with fine threads requiring a watertight fit (Source: DI Labs)

As-Printed Threads

Now let’s turn to as-printed threads, which will eliminate the added steps and labor of tapping and inserting, and can be an ideal option for parts that will be assembled with screws just once or rarely, not repeatedly.

If you are printing threads into the part, the bigger the thread the better.

When it comes to the smallest threads that will function as printed, this will vary based on the speccific machine and machine settings you’re using. The best approach is to consider the requirements of the applications and let that guide the method of creating threads.

You’ll also need to make sure that the threads you’re using can build successfully without supports growing between since supports between the teeth of the threads that can’t be removed completely will impact thread functionality. Even when the build is oriented so that the threads print vertically, this doesn’t always guarantee that threads will be printed without supports.

Make sure to check on the minimum feature size of the material and technology you choose. Any areas of the thread that taper below this minimum size will not form. If you’re taking minimum feature size into consideration, chances are good that the threads will work as intended.

In any case, always account for post-processing when designing and printing threaded holes. For example, how much warpage or shrinkage should you expect? Will your holes have support structures inside and how will removal affect the size or thread edges?

Article source : all3dp ,Chloe Vollaro

Image source : Formlabs ,3D People ,Markforged ,DI Labs