# Mechanical resolution of the Z axis

I’m looking how Velleman found a mechanical resolution of 0.781 µm to the Z axis while it is a M6x125 screw and 200 steps motor (1.8 ° / step)

If i do the calculation I get: 1.25 / 200 = 0.625μm.

However, I can find the value of 0.781 microns with the following calculation:

screw thread step / number of step to 1mm
1.25 / 160 = 0,781 microns

number of step to 1mm = value in the configuration file / driver microstepping
160 = 2560 / 16

But it’s a mistake, what do you think ?

M8
1,25 mm is 1 rotation or 200 full stepps (3200/16 stepps) by z-axis
1mm is 0,8 rotation or 160 full stepps (2560/16 stepps) by z-axis

and the entry is 2560 spepps per (1)mm
so i will get 0,39micron and this was the entry i had found in the 3Drag datasheet on reprap.org/wiki/3drag

And 1,25mm /200 Stepps = 6,25µm

@eytec : You are agree with me resolution is 6.25µm

But on 3Drag datasheet, it’s the same it’s specified :
Accuracy Diameter of nozzle 0.5 mm, - X e Y: 0,015 mm - Z: 0,39 µm Diameter of nozzle 0.020”, - X e Y: 0,00059" - Z: 0,39 µm

So half as K8200 (0.781µm). From where this value is coming from ?

PS: sorry for mistake on screw size M8 and not M6, and for calculate value 6.25µm and not 0.625µm, I search to find orign of mistake and I made mistake !!!

Yes full stepp size is 6,25µm but the stepper driver are coded to 1/16 of Full stepp
so 1,25mm / 200 / 16 = 0,390625µm
why they write down the 1/8 Full Stepp (0,781µm) ?

I think this resolution is not possible with a normal z-axis (tollerace) so they double this