3D printing threads is hard! Custom Threads in Fusion 360 makes it easy!
TLDR: Create threads in Fusion 360 with custom tolerances to allow for reliable 3D printing of threaded objects. Purchase my full set of ISO Metric profiles here: Fusion 360 ISO Metric Thread Profiles (w/ Tolerance) – ReplicantFX
Fusion 360 by Autodesk is simply amazing software. For those who do not know, it is free for personnel to use CAD software that combines the power of Solidworks with the flexibility of Sketchup and much more. There is a bit of a learning curve as it is different than either of those pieces of software but I assure you it is worth the time investment to learn.
One of the tools within Fusion 360 (F360) is a powerful threading tool. It is found under the Solid/Create Tab:
Pressing the thread menu item will present a form for customizing your thread:
From this form you can choose from a plethora of standard threads. My favorite to use is ISO Metric.
You should also note that you can select an option that models the threads or simply shows a texture.
Deselecting “Model” will show a thread texture instead and is great for large assemblies, easing up on computer power. For printing threads, select “Model” and Fusion 360 will actually create all of the geometry for real threads.
Unfortunately, customization of the threads stops at the provided profiles with no further customization available. They will print great (Look good), but you will discover that the tolerances are too tight for what a 3D printer can achieve. Users have found different ways of handling this. Often they create the threads and then scale the object axially. This can work, but is unpredictable and not a true, accurate tolerance addition, but a hacky way to “make it work”… sometimes. To take the guess work out and in some cases even make it possible to print threads, I needed a better way.
ISO Metric Threads w/ Adjustable Tolerances in Fusion360
After a little research I found that the F360 defines the threads using user accessible xml files. Available thread definitions can be found at:
C:\Users\%UserName%\AppData\Local\Autodesk\webdeploy\production\%Hash of Version%\Fusion\Server\Fusion\Configuration\ThreadData
You will need to replace the %text% in the above path with your user/install specifics. The “Hash of Version” will be a weird string of letters and numbers with little rhyme or reason. Additionally, this hash changes with each subversion, which will lead to some difficulty in maintaining current versioning.
If you open any of the files, you will see a human readable xml file. To make my life easier, I imported that into Excel. From there I created a custom macro to add tolerance and create custom profiles.
The large amount of data located in the table above are the values pulled from F360’s ISO Metric thread file. I used these as the base measurements and let my macro add and subtract fractions of millimeters to produce a true tolerance offset. The resulting adjustments resulted in threads as below:
In the example above you can see the original ISO threads, the Max/Min allowable thread sizes that are still in the official international standard (That Fusion follows) and our adjusted thread with custom tolerance suitable for 3D printing. Using this tool I then produced thread profiles with 0.1mm, 0.2mm … … 0.9mm and 1.0mm tolerances added.
There was a substantial time commitment to producing and testing these profiles. I provided all of my ISO metric profiles and test objects for purchase through my site at:
If you place any of these files in your F360 thread folder they will become available in F360. Using the above files, I generated 9 test nuts and bolts. These ranged from 0.0mm to 0.8mm tolerance in 0.1mm steps. I printed the set on an Ender3 in PETG and then took each for a threading test run. I could turn all of the nuts from 0.4mm to 0.8mm with the best “feeling” threads occurring at the 0.5mm tolerance level. On my machine, tolerances lower than that resulted in un-turnable threads. An STL file of the 9 nuts and bolts is also provided in the above file.
After all of this, I now have a reliable thread profile for my 3D printing projects. I have since used it for Light Saber hilts, CNC control pendants and even a mechanical vise! I wish (And have provided feedback to autodesk) that this becomes a standard feature, but 3 years on there has been no movement.