Guide to Printing Threads
Hey guys, I got my machine to print some really nice threads and just wanted to share the procedure with everyone:
1. Material: PLA; nozzle dia: .4mm
2. Print settings key points:
a. bed: 65 first layer and 55 for rest, nozzle: 215 for all
b. extrusion width: .4mm
c. speed: 50% first layer and 100% for rest
d. check the "generate support material" box for thread support
3. There are two useful charts located at "engineersedge.com" that need to be used to accurately size the external threads (bolt) and internal threads (nut). For the external, to ensure a proper fit that's not too tight and to compensate for the inaccuracy of the printing process, you need to use the MINIMUM MAJOR DIAMETER for the diameter of the shaft. Then, insert CUT threads of your choice. This will draw the edges of the threads back leaving a slight gap between each thread's engagement (allowing it to turn smooth and not lock up/ cross thread).
For the internal, you need to use the MAXIMUM MAJOR DIAMETER for the chosen thread size, then EXTRUDE internal threads. Make sure you pay attention to the "Tolerance Class" column and use the same one. For example, if your thread is a M25x2.0 with an external tolerance class of 6g, then you will want to use an internal thread of the same size with a 6h tolerance class.
This allows enough room for the bolt to spin smoothly inside the nut. Here are the links for each metric chart (there are standard charts as well):
http://www.engineersedge.com/hardware/metric-external-thread-sizes1.htm
http://www.engineersedge.com/hardware/metric-internal-thread-sizes0.htm
As for the thread design process, I personally use Solidworks and have an installed thread wizard with preloaded profiles, but there are several videos on how this is done in various programs. Hopefully this helps, and if there is anything I left out, please feel free to add to it!