RE: Motor step angle and screw pitch for MK3: 1.8* and .8mm?
@philippe-m11
The magic number should be calculated using the number of natural steps in 360 degrees and distance traveled in Z per full rotation. Given the 1.8 degree step of the Prusa i3 MK3S motor, the number of natural steps is 200. Given the 8mm diameter rod with a lead of 8mm, Z will move by 8mm per complete revolution. The magic number is (Z distance travel/steps per full rotation) = 8/200 = 0.04 mm. As such, your layer heights should ideally be divisible by 0.04 mm. This will avoid any possible variation in height thickness in the resulting print due to micro-stepping variations. A somewhat decent discussion of this is here: https://www.youtube.com/watch?app=desktop&v=WIkT8asT90A . Note that the video referenced above includes an example of a print done at 0.10mm and 0.12mm thickness, where the 0.12mm was a multiple of the magic number for the Ender 3 he was using. Under a microscope you can see the variations in the layer thicknesses that resulted with using the 0.10mm layer height.
RE: Motor step angle and screw pitch for MK3: 1.8* and .8mm?
I started doing some more systematic tests of the effect of magic numbers, see http://repstrapdk.blogspot.com/2021/01/tests-of-magic-numbers-part-1.html. Will post again when I have more results.