Working on a 4th rotating axis
Wil do it with a 38:1 worm gear because i have no better

with a 0.9 degree/step motor
360 / (400steps x 38ratio) = 0,024 degree

on a diameter of 20mm thats 20 x 3.14 / (400steps x 38ratio)  =  0,004mm
on a diameter of 50mm thats 50 x 3.14 / (400steps x 38ratio)  =  0,01mm
on a diameter of 100mm thats 100 x 3.14 / (400steps x 38ratio)  =  0,021mm

Ordered a few bearrings to make the 8mm axis
to rotate smooth and playfree
              

Disconnected the X-axis and connected this rotating axis as X-axis
First try
Text is wrong because axis whas turning wrong way
have to change wires of the steppermotor

First try
Text is wrong because axis whas turning wrong way
have to change wires of the steppermotor

Second try
changed motor wire and resolution from 0,0015 to 0.001mm