What To Do When 3D Printed Threads Don’t Fit

Designing and printing 3D threads that match the targeted screw is an art that very few people have managed to master over time. There are many reasons why it could be challenging to get the perfect match, such as curved or jagged threads, slightly smaller prints, a wrongly configured printer, or warping filaments. 

When 3D printed threads don’t fit, you can re-design your thread pattern, adjust your printer settings such as print temperature and speed, or choose a high-quality, low-friction filament that is less prone to warping and shrinking. 

With that said, let’s have an in-depth look at how to get perfect 3D printed threads and avoid a situation where some threads don’t fit. I’ll help you diagnose your threads’ issues and teach you how to fix the most common problems with 3D printed threads so that you can get a secure screw-in every time. 

Why Don’t My 3D Printed Threads Fit?

So, you’ve designed and printed some threads, and although you did your due diligence in design and development, they just won’t work. 

Threads are tricky to 3D print since they have such minute detail and exact geometries, so it almost always takes a few times to get your design right. However, printer errors, filament warping and stringing, and many other factors can ruin a perfectly designed thread pattern. 

Your 3D printed threads don’t fit because you may have gotten the measurements wrong, or they may have a block due to a printer miscalculation, filament stringing, or artifacts. Otherwise, the threads may have warped or shrunk during cooling. 

So, we can narrow down this thread problem to three probable causes – faulty design, a printer error, or a filament-related issue. Luckily, these problems are all fixable with the right amount of dedication, so don’t give up yet! 

How To 3D Print Threads For The Perfect Fit

Well-crafted 3D printed threads should always fit their respective socket. However, due to some miscalculations and errors, you might have to deal with a situation where one doesn’t perfectly fit. 

I hate to be the bearer of bad news, but if your threads don’t fit now, you’ll probably have to start again from square one and go back to the design process. 

So, let’s look at some of the things you can keep in mind to ensure that your threads work straight off the bed:

Design Your Threads Accurately and Precisely

If you are printing threads, the measurements must be flawless for your print to work. So, you need to pay extra close attention to each dimension of your threads, screw, and socket.

If you can find a pre-made template for your threads, I highly recommend using one. For instance, cloud-based 3D modeling like Fusion 360 lets you design ACME screw threads that fit perfectly. 

However, if you want to learn, you may want to watch this youtube video from Product Design Online to see what it entails: 

Use Thread Geometries That Work For Plastic

Threads are not a one-material-fits-all deal. Some geometries (or thread patterns) work better for plastics, and others work better for metal threads. That’s why, if you compare manufactured plastic threads with metal screws, you’ll see that the plastic has smoother, wider thread curves with rounded ridges. 

This plastic thread design is called SPI Neck Finish, and it is optimal for 3D printed threads. Since these thread patterns have smoother edges and don’t create much of an overhang, your 3D printer likely won’t have an issue printing them. 

However, there are some cases in which you might need to screw your 3D printed threads into a metal socket, which is when things get a little trickier. In this case, you’ll need to use a metal thread design with plastic. 

Consider Your Nozzle Size and Layer Height

Sometimes, your lowest layer height won’t be small enough to produce intricate, narrow threads. Nozzle size and the lowest possible layer height that your printer can manage are significant limiting factors when printing threads since you probably won’t be able to make tiny, detailed screws or nuts. 

So, be sure only to design a thread that your printer can handle. Otherwise, you’re setting yourself up for failure. 

Find the Optimal Temp Range for Your Filament To Prevent Warping

Using the improper temperature settings will often cause your 3D threads to warp or bend after printing, making their crests uneven. 

That’s because high temperatures make considerable changes to your filament, and if it cools too quickly or too slowly, the plastic may shrink or expand at an odd rate, bending in the process.

Alternatively, you can invest in a better cooling system or re-evaluate the fan settings you’re using. Some filaments such as ABS are prone to warping because of their ideal print temperatures, and using the fan too heavily can expedite this bending. 

So, essentially, know your filament’s ideal hot end and print bed temperatures before you try to print something as complicated as a screw. Once you find the “sweet spot” where a thin-walled print doesn’t warp, you can graduate to printing threads. 

Reduce the Printing Speed

When you print your threads too quickly, you increase the chances of stringing and artifacts, which will block the grooves, making your 3D print useless. 

Threads are prone to stringing anyway, so being cautious and slowing down the print speed can save your screw from the recycling machine. 

I’ve found that using the lowest speed recommended by the filament’s manufacturer will do the trick. However, you may need to slow things down more depending on your filament choice and your 3D printer, so do some testing to find the right setting for you. 

Start Using Better Filaments

When you choose a filament or resin to make threads, you’ll need to consider a few factors. 

Firstly, your material shouldn’t be prone to warping. For that reason, you may want to avoid using ABS to make threaded parts. Instead, opt for something like PLA, nylon, or PETG. 

In addition, you don’t want to use a porous filament to print threads. Rough or porous filament will add friction, making it challenging to screw and unscrew your 3D printed parts. In the worst case, the bond will be so tight that you’ll break the 3D-printed object while trying to unscrew it. 

Ideally, you’ll want a material that shines, as this indicates a slick, smooth surface that will reduce friction. Nylon and PETG work well in this regard, and PLA performs okay. In addition, to reduce friction, you’ll need to sand down your layer lines and give those threads a smooth surface. 

Alternatives To 3D Printing Threads

If you just can’t seem to print the threads you want, there are still a couple of options: 

• Use a tap or drill to cut threads into 3D printed parts. A tap like this QISF Adjustable Tap Holder (available on Amazon.com) will allow you to cut threads into your 3D print. This tap is simple and easy to use, and it comes with five standard thread sizes, so you can just cut the hole and then thread in a metal screw. 
• Use threaded inserts and metal screws on your 3D printed parts. Threaded inserts are a fantastic workaround for incorporating threads into your prints. These inserts pop into your model, allowing you to get the perfect size threads for each part. You have to leave enough room on your print to glue in the thread insert, then stick it in!

These alternatives are fantastic options for adding threads to 3D printed objects, and they take out the work of designing the geometries yourself. In addition, they usually last longer since you can use metal screws for a secure hold. 

Final Thoughts

So, 3D printed threads won’t work if you didn’t design them correctly or if your print speed, temperature, or nozzle weren’t suited for the job. Otherwise, your filament might not be up to snuff for threadwork. 

It’ll take a bit of troubleshooting to figure out where you went wrong, but hopefully, this guide has given you the knowledge you need to perfect your thread-printing skills. If not, there are always alternatives like thread inserts or a tap.