Z-axis move past home position before printing

Hi there,

I am building my first mendel prusa i2 and got everything running and working (calibrated). Using pronterface if I tell my x-axis to move 100mm it moves 100mm. I get the same result for the y-axis. If I tell the
Z-Axis to move 10mm it moves 10mm. All the axis both directions works fine. Using pronterface if I home any one of the axis it does so perfectly, and when I home all three together (bottom left option) it homes perfectly.
I am comfortable with the movement speeds of the axis and the current settings on the pulolo boards on my RAMPS 1.4.

My problem is when I try and print a file the z-axis moves past the homing position after its initial home. In other words, when I click on print (the temperatures of the hotend and bed is at the correct temeratures before I press print.),
all the axis home fine, and then pronterface waits for 10 seconds before it starts the print. But after this 10 seconds the z-axis moves down again, pressing the home switch, it seems to ingore the switch and moves down about 3-5mm more.
I am not sure by exactly how much, it is hard to tell.

I have tested this by moving the endstop for the Z-axis higher up and further away from the print bed, it still happens and for the life of me I do not understand why it would do that. I have only one extruder and I imagine home is almost always set to be paperheight above the print bed, why would the software want to move the z-axis past that 0 point and push the hotend into the heatbed?

What am I missing? I use slic3r to generate the gcode and can not see any settings I may be configuring incorrectly on there. I am pretty sure my Marlin code is set up correctly too.

Any input would be appreciated!

hello, I had the same problem and solved it by removing this line in the start g-code. I was using Slic3r

G1 Z5 F5000; lift nozzle (see pic)

also having the auto bed leveling activated in your firmware (if you don't have ABL ) will produce similar results.

Ray

Edited 1 time(s). Last edit at 05/25/2016 05:35PM by Shank man.

EDIT:

Thank you Ray!

Your screenshot has solved my problem!
Auto bed leveling is disabled in my Marlin FW, and I have read many posts where people mention this gcode nozzle lift issue. I then read on the slic3r documentation about gcode, and where I can edit it within the program, but could not find anything useful.

This has fixed my problem.
I am not sure why the nozzle would move DOWN when it states "lift nozzle", but I would probably just reverse the axis in the FW if I needed that function.


Again, thank you for pointing out where in the slic3r configuration I can fix this issue.

Edited 1 time(s). Last edit at 05/26/2016 03:14AM by v1talogy.