Print Working ISO Standard "M" Threads

thingiverse

Using the ISO standard as described in the attached ThreadTech diagram, I was able to print very usable screw threads using PLA, at 0.2 line thickness. The ONE adaptation needed is that I had to increase the diameter of the female thread by 0.8mm. This gave me threads that mated with very little resistance (almost zero). I could probably have safely decreased the diameter difference to 0.6mm. Note that at a diameter difference of 0.4mm, I was not able to screw the nut and bolt together. [See my design notes on how this could be improved.] I did my experiment using a male effective diameter of 3.4cm with a 3mm thread pitch (P). In ISO terms, this is expressed as M34 x 3.0. I included a screen shot from Blender which shows the profiles of the male and female threads, with the above mentioned spacing of 0.4mm radius (0.8mm diameter). P=3mm in this example. An additional design component of working threads is that the mating ends of the thread shafts should be "camphered" at 45 degrees. This is equivalent to shaving off the edge of the outermost threads with a 45 degree conical surface. The purpose of the campher is to make the threads of the two parts self-centering, and to align the two parts along the same axis, which will help avoid thread stripping. Conclusion: Given the diameter spacing adaptation required with printing tolerances with current technology FDM techniques, it would be challenging to get ISO thread diameters to be functional below a male M8 x 1.0.