Repetier said:
How did you print with slower speed? Did you reduce z max speed? I don't think xy speed for printing which you set in slicers matters here and for z some slicers rely on firmware reducing speed to a healthy limit.
The code does not depend on z so it behaves always the same. Only external influences can change what happens. E.g. a z max endstop triggering could stop a z move before finished.
I suggest to make some measurements for different Z to see where what happens. Lets say problem starts a 1mm and ends at 5mm go z=0 and then up 1mm, measure real distance, do this then z=0 -> 2 .. 10 and compare results. Also hear if you hear some lost steps. It might be ok going from 0 to target but fail to go from1 to 1.1mm - then acceleration in that area looses steps.
<font face="Arial, Verdana">I just tried to move the extruder up from z=0 step by step</font>
<font face="Arial, Verdana">g28</font>
<font face="Arial, Verdana">g1 z0</font>
<font face="Arial, Verdana">G4 P1000</font>
<font face="Arial, Verdana">g1 z0.4</font>
<font face="Arial, Verdana">G4 P1000</font>
<font face="Arial, Verdana">g1 z0.8</font>
<font face="Arial, Verdana">G4 P1000</font>
<font face="Arial, Verdana">g1 z1.2</font>
<font face="Arial, Verdana">G4 P1000</font>
<font face="Arial, Verdana">g1 z1.6</font>
<font face="Arial, Verdana">G4 P1000</font>
<font face="Arial, Verdana">g1 z2</font>
<font face="Arial, Verdana">G4 P1000</font>
<font face="Arial, Verdana">g1 z2.4</font>
<font face="Arial, Verdana">G4 P1000</font>
<font face="Arial, Verdana">g1 z2.8</font>
<font face="Arial, Verdana">G4 P1000</font>
<font face="Arial, Verdana">g1 z3.2</font>
<font face="Arial, Verdana">G4 P1000</font>
<font face="Arial, Verdana">g1 z3.6</font>
<font face="Arial, Verdana">G4 P1000</font>
<font face="Arial, Verdana">g1 z4</font>
<font face="Arial, Verdana">G4 P1000</font>
<font face="Arial, Verdana">g1 z4.4</font>
<font face="Arial, Verdana">G4 P1000</font>
<font face="Arial, Verdana">g1 z4.8</font>
<font face="Arial, Verdana">G4 P1000</font>
<font face="Arial, Verdana">g1 z5.2</font>
<font face="Arial, Verdana">G4 P1000</font>
<font face="Arial, Verdana">g1 z5.6</font>
<font face="Arial, Verdana">G4 P1000</font>
<font face="Arial, Verdana">g1 z6</font>
and I found that between about 2mm to 4mm the extruder is moving shorter distance than it should be. I think it will also happen if I reduce the height of z max length. And there is no weird sound which indicates any slide. I'm still wondering there is something wrong in the arduino firmware. Is there anyway I can reinstall the program in arduino in order to fix this problem? Thank you.