Need help with Auto bed leveling.

Sazabi

Hi there,

I've moved to inductive Z-probe recently and decided to activate auto bed leveling feature. I've spend a day trying to understand and configure it. But no luck. And I really need your help.

Here's what I have:

- Repetier firmware 0.92.9.

- probe offsets are 20/60 (yes, sensor is bg, I had to move it this far, moves with hotend).

- Table dimensions (keeping probe above table) 280*160mm

- ENDSTOP_Z_BACK_ON_HOME 10

- Z_PROBE_BED_DISTANCE 10

- Z_PROBE_HEIGHT 2.2

- BED_LEVELING_METHOD n*n grid, grid size 5, probe pos.1 20/60, probe pos.2 280/60, probe pos.3 20/160.

If I home all axis, keep hotend at 0/0, and try to run G32, hotend hits endstops making mechanics crack. If after homing I move hotend to, i.e. 100/100 (X/Y), than running G32 makes hotend move in probe coordinates 20/60 (which is physically hotend and table 0/0).

Why does it forces hotend to move beyond 0/0 after homing? If I put first probe pos.1 to 0/0, it also tries to break the limits despite of hotend placement.

Another thing I don't understand is:

Having ENDSTOP_Z_BACK_ON_HOME 10 makes print run (tried on dry run) 10mm above the table. Making ENDSTOP_Z_BACK_ON_HOME 0 helps. But with it in 0, I have to manually move Z axis to prevent plastic blob on hotend.

MartinH

First, i recoend using the dev version of firmware, many improvements in probing .

Use homing option z up X Y Z this will open a section in config tool where you can set the X Y coords for z homeing.
setting ENDSTOP_Z_BACK_ON_HOME 10  artifitially moves the Z0 position to 10mm off the endstop trigger point.

Sazabi

MartinH said:

First, i recoend using the dev version of firmware, many improvements in probing .

Use homing option z up X Y Z this will open a section in config tool where you can set the X Y coords for z homeing.
setting ENDSTOP_Z_BACK_ON_HOME 10  artifitially moves the Z0 position to 10mm off the endstop trigger point.

Sir,

Option Z up X,Y, preheat,Z opens XY Homing pos. for Z option. By default those are 999999. But note says - [mm / 999999 = do not change]. So I asume these coords shouldn't be changed?
And for the ENDSTOP_Z_BACK_ON_HOME 10 - how could I make Z axis to drop table 10mm after Z homing without ruining Z0?

MartinH

yes you can change them, then nozzle will move up the set amount and move to the X Y co'ords that you set instead of the 999999

MartinH

I run homing and bed levelling from the script option buttons,

homing just send  G28

levelling, i like to make sure the sensor is over the bed before it starts ,so i set in button 2
G1 Z10 F700
G1 X30 Y30 F1200
G32

Sazabi

MartinH said:

I run homing and bed levelling from the script option buttons,

homing just send  G28

levelling, i like to make sure the sensor is over the bed before it starts ,so i set in button 2
G1 Z10 F700
G1 X30 Y30 F1200
G32

Can you share how you probe offsets and bed leveling method/probe positions configured?
About homing and lifting Z axis a bit (to keep nozzle clean from plastic blob) - is parameter ZHOME_PRE_RAISE_DISTANCE (appeared when I select Z up X,Y, preheat,Z) what I'm looking for?

MartinH

ZHOME_PRE_RAISE_DISTANCE    this will raise Z before it does the homing, so Z allways needs to have this amount of clearance (below Z max)
G28 ends the homing with a move to X0 Y0 Z0

You could use one of the preset buttons and do

G28
G1 Z5

Sazabi

Ok, I've flashed dev firmware. Left everything as it was, except homing procedure as was stated by MartinH. ZHOME_PRE_RAISE_DISTANCE is 10mm. While homing I get message in repetier, that  hotend is trying to reach unavailable coordinates (-20, -60 - just same as z-probe offset. But why? Should I change X_MIN_POS and Y_MIN_POS to probe offset coords? Why with activated probe all coordinates conects to probe, not hotend?

Repetier

No, you need to set z homing position to 20, 60 to make it work. Guess you home xy being at 0,0 and then it activates probe which means moving to -20,-60 from 0,0 and that is not possible.

Select a homing order with preheat and set preheat temperature 0. That option also allows setting z homing position which is what you need.

Sazabi

Thanks, that helped.
Few more questions:
- Tools-Bed height map makes Host to crash. Runing with 5*5 points. Crushes on about half way done.
- Z_probe_height -1.000. I have inductive probe and alu table. When I try to home Z axis, it crushes into table on first try, but that stops on the correct height. How to prevent this first time probing from breacking my table?:) Looks like it ignores Z_Probe_Height. 

Sazabi

Moved z-probe lower, looks like it works.