ABL testing outside of bed boundary

I've just upgraded the controller on a Tronxy X3A to a RAMPS 1.4 leaving everything else apart from the z-Probe intact.

I have configured the Marlin 1.1.8 firmware for everything I believe I need to.

The problem is when I try to do Auto Bed Levelling, the mesh starts out within the boundary of the bed, but then starts trying to sense outside the bed.

I have tried both linear and UBL types of ABL. They both try to sense outside the bed boundary. The home is correctly set, although it is at X:155 Y:120 Z:10. I have the x, y and z offsets correctly set so that when I do a G1 X0 Y0 Z0 the nozzle ends up precisely on the left front corner of the bed with a paper's width between it and the bed.

The configuration.h is attached.

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Printer: Tronxy X3A (modified)
Modifications: Replaced Z-Probe with an NPN LJ12A3-4-Z/AY
Upgraded Melzi to RAMPS 1.4 with Arduino Mega 2560

Why is home set at X155,Y120,Z10 ?

If the X endstop is on the left and the Y endstop is at the back then theses are min endstops so x,y home should be 0,0 (or a negative value if the nozzle is off the bed at home).

Hi,

I have no idea why the home values for X and Y are the way they are. All the endstops are min ones. The x is on the left and the y is at the back of the bed.

All I did was download the Marlin firmware and configure configuration.h to get it working with the printer I have. It is largely a Tronxy X3a stock printer but with the mods detailed below. This is also my first attempt at 3D Printing, although I have about 35 years experience in IT and engineering. I couldn't find anywhere in configuration.h or adv.h that lets me define the home location. But, the big problem is the offset of the ABL mesh. I printed a G26 test, last night and found it started OK, but when it had finished, the left side of the print was right on the left edge of the bed and the front was about 50mm in front of the bed edge, so the front two rows of circles were printed in thin air. This seems to match up with the position of the ABL mesh used for testing.

So any pointers or help would be greatly appreciated. I suspect I have overlooked something glaringly obvious and will probably look a total fool when I find out, but I don't really care.

The reason I chose a kit that has not had exceptional reviews is that I figure I will learn a lot more by getting it working than if the printer worked straight out of the box.

Mark

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Printer: Tronxy X3A (modified)
Modifications: Replaced Z-Probe with an NPN LJ12A3-4-Z/AY
Upgraded Melzi to RAMPS 1.4 with Arduino Mega 2560

The home positions are set in the printer host program and the slicer. ie. repetier host/matter control/slic3r etc.

Take a look Here on the page 'Getting parts centered on my print bed'

OK, I followed the instructions you pointed at, but it did nothing for the home point and the ABL mesh is still off the bed at front and left. I managed to get the home corrected and doing a G1 X0 Y0 Z0 perfectly aligns the nozzle with the front left corner of the bed and is persistent across restarts thanks to the M206 and M851 commands.

I really need to get the ABL sorted as the Tronxy has a really unstable Y-Axis being mounted on a set of V-wheels on opposite sides of some 2020 extrusion, rather than two parallel linear rails under the bed (that's my next mod together with a leadscrew for the Y-axis motion to replace the belt and gear arrangement).

When I do a G28, it still ends up at x:140 y:92, which I don't understand. When I had the Melzi board in, the home position was much nearer the centre of the bed than this. This seems to be offset by a similar amount to the ABL mesh.

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Printer: Tronxy X3A (modified)
Modifications: Replaced Z-Probe with an NPN LJ12A3-4-Z/AY
Upgraded Melzi to RAMPS 1.4 with Arduino Mega 2560

When the print head is on the x and y endstops. How far is the nozzle of the bed -x and - y ?.

Can you post your current configuration.h and configuration_adv.h.com

To get G28 to go to the centre of the bed,you have to set the bed size in the config

With the X & Y home set to the corner of the bed, the min endstops are at X-15 and Y-28, the inverse of which are what I used to offset the X & Y home points.

I've attached both the requested files to this message.

Edited 1 time(s). Last edit at 04/25/2018 07:15AM by Scoundrel666.

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Printer: Tronxy X3A (modified)
Modifications: Replaced Z-Probe with an NPN LJ12A3-4-Z/AY
Upgraded Melzi to RAMPS 1.4 with Arduino Mega 2560

Try setting in configuration.h

// Travel limits (mm) after homing, corresponding to endstop positions.
#define X_MIN_POS -15
#define Y_MIN_POS -28


allso, you UBL grid should be coords for pt1= front left
pt2=front right
pt3=back left

so try
//===========================================================================
//========================= Unified Bed Leveling ============================
//===========================================================================

#define MESH_EDIT_GFX_OVERLAY // Display a graphics overlay while editing the mesh

#define MESH_INSET 10 // Mesh inset margin on print area
#define GRID_MAX_POINTS_X 6 // Don't use more than 15 points per axis, implementation limited.
#define GRID_MAX_POINTS_Y GRID_MAX_POINTS_X

#define UBL_PROBE_PT_1_X 15 // Probing points for 3-Point levelling of the mesh
#define UBL_PROBE_PT_1_Y 45
#define UBL_PROBE_PT_2_X 170
#define UBL_PROBE_PT_2_Y 15
#define UBL_PROBE_PT_3_X 15
#define UBL_PROBE_PT_3_Y 190

You are my Jedi Master, Obewan! The advice you gave fixed the UBL problem I was having. The mesh now sits firmly on the bed and goes from edge to edge without spilling over. I did have a couple of instances where the print head tried burying itself below the bed, but a couple of resets fixed that. Now I can move on with my next mods, a more stable Y-axis with rails and leadscrew rather than v-wheels and belt, and stabilising bearings at the top of the z-axis leadscrews and redesigned x-axis mounts.

Thanks again for all your help.

Edited 1 time(s). Last edit at 04/27/2018 04:47PM by Scoundrel666.

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Printer: Tronxy X3A (modified)
Modifications: Replaced Z-Probe with an NPN LJ12A3-4-Z/AY
Upgraded Melzi to RAMPS 1.4 with Arduino Mega 2560