I have printed two cubes with 20 mm and 40 mm edges.
When measuring the printout I get the following:
20 mm cube:
X: 20,02 mm (OK)
Y: 19,9 mm
Z: 20,5 mm
40 mm cube:
X: 40,02 mm (OK)
Y: 39,9 mm
Z: 40,5 mm
I seems that there are absolute faults: 0,1 mm i the y-axis and 0,5 mm on the Z-axis which is not acceptable for my purpose.
I’m using 0,2 mm resolution that should result in varying results, but it is always less in Y and too much in Z. The Z-fault is the most annoying for me. Using PLA (210 deg) and a heatbed with Buildtak at 50 degrees, Cura slicer, 20% density and half speed. All other settings: default.
I assume the large z defect is due to the straight connected rod to the stepper… And it’s limited to the amount of steps the stepper can do in 1 revolution. Which doesn’t exactly is 0.2 mm but more in the 0.2025 range (don’t exactly know need to look a bit for the exact value somewhere around this forum.) this is the z part of your problem I think.
Since its not a relative fault there is not a gear-ratio problem. I have found possibilities to adjust hight of first layer and also the nozzle distance to heat bed. My work-around solution is to cut 0,5 mm (using netfabb) from the bottom of the model.