ABL Problems on i3v 8"

[mwyrick]

I have an i3v 8" that I have added clough42's (thingiverse 335632) onto and now I am working on the code. Like most other I ran into problems and have a few questions.
Using a RAMPS with Mega 2560.

The code I am using is https://github.com/beckdac/Marlin on the Marlin_V1 branch checked out a few days ago. I made a few changes as shown in the attached configuration.h file.

EEPROM is disabled
SAFE_HOME is turned on, It can't be off due to the same problems others have that when it is turned off the Y axis will move with the initial Z upwards movement throwing the Y axis off.

This part only deals with G28, Not a following G29.

My first question is should the Z_PROBE_OFFSET_FROM_EXTRUDER have any real world meaning or it it just set to a value that will put the print head where it needs to be. I ask this because I have measured with calipers the real offset from the print nozzle to the switch as 3.9mm (nozzle is higher than the switch). But when following what others do I have to put -7.9 into the configuration.h file to bring it back down to the bed height. I have watched that the G28 code once done finding the "zero" position will raise the Z axis higher than the 5 mm it thinks it was told to move. This is confirmed by measurement after the move and by the number of rotations the Z motors due. The move is 9 mm up, but the code thinks it only moved 5 mm (the Z_RAISE_BEFORE_PROBING) value so after the homing it sets Z to 5mm then adds the -Z_PROBE_OFFSET_FROM_EXTRUDER to that value. The extra 4mm I have to put into the OFFSET lets things "work". I have traced the code and found it does think it is told to move 5mm but looks like the plan_buffer_line code is messing that up. This same code also seems to be what is causing the Y axis to move when the G28 code has not told it to.

So does anyone's offset match the real world offset? After the G28 command, if I raise the Z Axis by 10mm it does indeed go 10mm.

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That is only using the G28 command. If I do a G28, then a G29 the 4mm is no longer a problem and my offset matches real world. I would prefer to get the G28 command working on its own so I don't always have to level.

- M

Still working on cleaning this up a little.

[INFO] SENT: G29 V4 T
[INFO] RECV: Roxy's Enhanced G29 Auto_Bed_Leveling Code V1.81:
[INFO] RECV: Full support at http://3dprintboard.com
[INFO] RECV: Bed x: 20.00 y: 20.00 z: 3.44
[INFO] RECV: Bed x: 97.00 y: 20.00 z: 3.62
[INFO] RECV: Bed x: 174.00 y: 20.00 z: 3.65
[INFO] RECV: Bed x: 20.00 y: 97.00 z: 3.56
[INFO] RECV: Bed x: 97.00 y: 97.00 z: 3.70
[INFO] RECV: Bed x: 174.00 y: 97.00 z: 3.69
[INFO] RECV: Bed x: 20.00 y: 174.00 z: 3.63
[INFO] RECV: Bed x: 97.00 y: 174.00 z: 3.70
[INFO] RECV: Bed x: 174.00 y: 174.00 z: 3.66
[INFO] RECV: Eqn coefficients: a: 0.00 b: 0.00 d: 3.49
[INFO] RECV: Mean of sampled points: 3.628222
[INFO] RECV:
[INFO] RECV: Bed Height Topography:
[INFO] RECV: +0.02253 --0.00897 --0.18622
[INFO] RECV: +0.06628 +0.06853 --0.06797
[INFO] RECV: +0.03028 +0.07153 +0.00403
[INFO] RECV:
[INFO] RECV: planeNormal x: -0.00 y: -0.00 z: 1.00
[INFO] RECV:
[INFO] RECV: Bed Level Correction Matrix:
[INFO] RECV: 1.000000 0.000000 0.000799
[INFO] RECV: -0.000000 1.000000 0.000603
[INFO] RECV: -0.000799 -0.000603 1.000000
[INFO] RECV: ok
[INFO] RECV: echo:endstops hit: Z:3.66