Minimum layer thickness and its multiples

Hi guys!
I’ve been reading several topics in this forum and could not find a clear answer to one of my doubts regarding my Maker Select Plus with BLTouch 3.1 and ADVi3++ version 4.0.6.
As far as I understood, the minimum layer thickness is 0.04mm due to the minimum step of the Z axle step motors profile. The printer states its minimum level as being 0.1mm. I guess that any layer thickness should be a multiple of 0.04mm, or 0.08mm, 0.12mm, and so on. How does the printer interpret the 0.1mm height? Does it adjust to 0.08mm? Since then I’ve started using 0.08mm in Cura slicer instead of 0.1mm but I’m still a little bit confused about these layer settings. If anyone could provide me an explanation, it would be highly appreciated.
Thanks

Hi guys! No clue about this subject?

The thickness of plastic is not the same than the minimal movement of the Z motors. It is related, but far complicated than that and it is also related to your nozzle (the diameter).

Also, even if theoretically the step motors can make a movement of 0.04mm, the printer is far from perfect from a mechanical point of view and you never get a perfect 0.04mm move.

But 0.04mm is not the actual theoretical minimal value because there are micro steps. In the case of the motors used by the i3 Plus, there are 16 micro steps per step, or 400 steps per mm (you can see this value under Settings / Motors / Steps). So the minimal increment is 1mm/400 = 0.0025mm.

Regarding more precisely the answer to your question, the computation is:

lroundf(z * settings.axis_steps_per_mm[Z_AXIS])

Regarding lroundf: "the nearest integer value to arg , rounding halfway cases away from zero, is returned.

So in your example (0.1mm), we have:

0.1 * 400 = 40 micro steps without any rounding.

Again (sorry to insist on this), this (rounding) has no actual incident on the print due to many other mechanical factors (and some are non-linear). From my understanding (I am not an expert on this subjects at all), the diameter of the nozzle is far more important to get in practice a better resolution.

Thank you, Sebastien!
Your explanation was perfect. I was wondering why you have set 0.04mm as minimum distance when adjusting the BLTouch and now everything is crystal clear.

This is quite arbitrary. I thought it was a reasonable value but I now think it is too high. I may change that in version 5.