For years, the ability to create a realistic thread in SolidWorks was something of artistic fantasy; a way to demonstrate your proficiency in SolidWorks. The rebuild times on a small assembly would be long enough to get a warm beverage, and on larger assemblies it would be long enough for me to fly somewhere on vacation. Nevertheless, with the arrival of 3D Printers, the need to create very accurate 3D CAD models of threaded parts is less fantasy and more reality. Of course, there are no shortage of videos out there demonstrating how to model threads in SolidWorks. However, to my knowledge, none of them focus on any sort of “best practices” for creating a thread for 3D Printing.
Some testing we had previously done here at Javelin led us to some pretty complex calculations regarding offsets and gaps at Maximum Material Condition (MMC), but at the end of the day we found that the most reliable method was just to model up the threads slightly oversize, then run the printed part through a tap and die set. Having the threads already modeled up helped to guide the part into the die for a “final” cut. This would also allow it to work accurately with traditionally manufactured parts.
Here’s a video showing how to add the threads to an M6x1.0 Socket Head Cap Screw (SHCS):
Rather than use up a bunch of time making the body for my screw, I was able to simply open the appropriate fastener from the Toolbox by right-clicking on it and choosing Create Part from the menu. This allowed me to configure it to the desired size.
For more information about the utility I used to turn off the Toolbox flag for the part, please refer to this blog article.
To create the thread, I started by creating my Profile sketch. This would ideally come from a standards manual (such as the Machinery Handbook), not made up on the spot as I had done – particularly if you are not planning on using a tap and die set. I made sure to position it in such a way that it will begin cutting in space, rather than in contact with the part. This just protects against rebuild errors at the start of the cut. Then, I created a helix first by sketching a circle, then by using the Helix\Spiral command (Insert > Curve > Helix/Spiral). If it important to locate your helix in such a way that it starts on your sketch plane. This will result in the most predictable behaviour when creating a swept cut. If it does not start on the sketch plane, you will get a swept cut that goes in two directions, which can be difficult to manage. After you have your Profile sketch and your Path (the helix), create a Swept Cut.
I used a Revolved Cut for the undercut, but if you are 3D printing this then the undercut may be unnecessary (depending on your design intent, of course).