Auto Bed Level Providing Un-Even First Layer

Hi all, I have built a gMax 1.5 Printer, it is using Marlin and it has autobed level setup on it, but since installing the upgrade, not once has it provided a perfect first layer. The adjustments are measured using a 3 x 3 grid, when probing the results seem to be accurate to the actual print bed. However when the printer starts printing the first layer, EVER time, the first layer is no where near even, i always have 1 side too far from the bed, and the other too close. It's like the autolevel is compensating the wrong way around, where it should be going closer to the bed it gets further, and vice versa. I have scoured the net and come across a few similar instances of this, but there has never really ever been a fix for it, other than making sure the bed is as close to level physically as possible; which kind of defeats the purpose of autoleveling... im using 4mm toughened glass as my print surface, it is completely flat with no uneven spots.

Any advice is greatly appreciated.

Thanks

Alex

Edited 1 time(s). Last edit at 08/17/2015 09:19AM by xelad.

Hello,

Did you properly set the distance between the nozzle and the bed leveling probe in the firmware? if this distance is very wrong, for instance -50mm instead of 50mm in one axis, then I guess it could cause an issue similar to what you describe.

David.

I have never played with auto-level, went with a delta rather than cartesian printer. However my first thought was that perhaps the results from the leveling process were not being saved. So issuing a G28 to home the axis at the start of print (part of the sliced g-code) is clearing the results of the auto-level routine.

Quote
Kurzaa
I have never played with auto-level, went with a delta rather than cartesian printer. However my first thought was that perhaps the results from the leveling process were not being saved. So issuing a G28 to home the axis at the start of print (part of the sliced g-code) is clearing the results of the auto-level routine.

Yes, the purpose of homing is to set the position as x=0,y=0,z=0 (or another position if set otherwise in the firmware), so I do believe it removes previously stored info from bed leveling, But homing should occure before bed leveling, in your start.gcode, you should first have g28 and then g29. I checked a gcode file, and their is no g28 generated by the slicer, what slicer are you using?

Anyways, in case it could help, here is the start.gcode I am using both in cura and slic3r in order to use bed leveling:

G21        ;metric values
G90        ;absolute positioning
M82        ;set extruder to absolute mode
M107       ;start with the fan off
G28        ;move X/Y/Z to min endstops
G29        ;bed auto leveling
G92 E0      ;zero the extruded length
G1 F200 E6  ;extrude 6mm of feed stock
G92 E0      ;zero the extruded length again
G1 F100
M117 Printing...;Put printing message on LCD screen