tg73 / fusion-360-fdm-threads

Fusion-360-FDM-threads

Fusion 360's current selection of thread profiles aren't overly useful for those looking to design parts that will be 3D printed. Standard 60 degree V threads can be printed satisfactorily by decreasing print speed or increasing cooling. However their tolerances are still machining centric and thus can be difficult to print at times.

Thankfully a workaround exists where custom thread profiles can be loaded into Fusion 360. The workaround is explained in this Autodesk support article. Something not mentioned in this article is that the process needs to be repeated each time Fusion updates. I've found it much easier to just search for one of the common thread profiles (such as ACMEScrewThreads.xml), than trying to navigate to the latest release folder.

Given the above I decided to write a simple script that would generate custom thread profiles that are more conducive to 3D printing. The profiles are trapezoidal in nature with root and crest flats 1/4th the width of the thread pitch. This yields robust threads that will not break easily. The included thread angles are 50, 60, 70, 80, and 90 degrees. For reference the overhang angle of a thread printed in the vertical orientation is 90 - (threadAngle/2) degrees.

Since many are not familiar with thread classes(tolerances) I tried to make the classes self-explanatory. When you select the class drop down you will see 0.###e for external threads, and 0.###i for internal threads. 0.### is the tolerance in millimeters compared to the nominal thread form. External threads are smaller than the nominal, and internal threads are larger than the nominal. If you designed a bolt with a class of 0.100e and a nut with a class of 0.100i, they would have a 0.1 + 0.1 = 0.2mm tolerance/gap between them when threaded together.