Print Working ISO Standard "M" Threads

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.

Printer Brand:

Prusa

Printer:

Prusa Mk2

Rafts:

No

Supports:

No

Resolution:

200 um

Infill:

15%

Notes:
I printed with the axis of the thread shaft on the vertical. I used PLA.

How I Designed This
I use blender.

I used 16 steps per revolution of the thread profile around the vertical axis. I recommend increasing the number of steps to 32 to improve the fit of the screw threads. I suspect that the excessive resistance that I experienced with a diameter difference of 0.4mm was substantially due to the relatively coarse mesh of the model.