Z Calibration

The AON-M2 uses active bed leveling while printing to compensate for any irregularities that may occur in the bed surface. A detailed description of this feature can be found in the Operation section, under Auto Bed Leveling. This page will explain how to use this feature.

Preheat Time

Before probing a mesh, it is necessary to allow the machine, both bed and chamber, to reach thermal equilibrium.

Preheat your bed and chamber to the desired printing temperatures. Use the Standard Preheat Times found in the Operation section to wait for the machine to reach a steady state. Note that it is necessary to wait for the full recommended preheat time, rather than waiting only until the bed or chamber has reached its target temperature on-screen.

Filament Retraction

Before probing, make sure the filament has been removed from the meltzone of the hot end. The meltzone refers to the area between the nozzle and heat break of the heater block assembly where the filament is actually melted. The filament can be removed from the meltzone by heating to the material’s operating temperature, extruding until material begins to come out of the nozzle, then retracting by 20 mm.

Failure to retract the filament will make it much more difficult for the hot end to trigger the bed probe mechanism. This will introduce errors into the calibration results and may damage the hot end and probe assemblies.

Nozzle Temperature

Probing requires lowering the hot end temperature so as not to damage the plate or cause the material in the hot end to break down and clog the nozzle. Lower the hot end temperature to 200ºC.

Homing the Machine

Before probing, the machine axes should be homed. On the touchscreen interface, navigate to the Motion tab under the control menu. Home the machine by tapping the HOME XYZ button. Once the machine is homed and probed, do not home again before printing as this can introduce error in the calibration.

System UI Home Procedure

Probing a Mesh

The Z Calibration tab can be found under the control menu. Here you can enter custom values for the probe bounds and grid size for the mesh, send the command to probe, and also adjust the Z offsets.

Z Calibration tab overview

The Z Calibration tab was added in application version 2.3.0. In the Settings menu of the user interface, check the Updates tab to make sure your software is up-to-date. Contact our Customer Success team at help@aon3d.com if you need help updating your software.

Probe Bounds

To customize the probing sequence, set the limit values of each axis (front/rear and left/right) where the number is the distance in millimetres relative to the (0,0) origin located at the front left corner of the build platform.

The X and Y Counts are the number of points equally distanced on each axis that will be used to build the leveling grid. A higher count adds more definition to the grid.

In the diagram below, you can see the coordinates of key points on the build platform to help plan your probing sequence. The blue square shows the outline of the printing area of the AON-M2 Aluminum Build Plate. Inside the blue square is the PEI plate outline and bolts on the AON-M2 High Temperature Build Plate.

Build plate X and Y coordinates

The default bounds for probing are:

Probe Bound Default Value
Left 35
Right 415
X Count 8
Front 35
Rear 415
Y Count 8

If you are using the AON-M2 High Temperature Build Plate, you must take extra caution to adjust the probe bounds. Do not probe outside the default bounds to avoid probing outside the area of the PEI plate as this can cause the bed to crash on the toolhead and damage it. The default grid created by the probe bounds will probe around the bolts holding the PEI plate to the aluminum base. Avoid using bounds that will probe directly on a bolt head as this will introduce significant error in the resulting mesh.


The dots represent the number of probing points selected. The lines are the boundaries of the defined probing area.

Probe Bed with Tool

This will initiate the probing sequence for the selected tool. Each point will be measured several times. Once you are ready to probe, tap the button for the desired tool.


This will stop the probing sequence. The active toolhead will go back to its initial X position. Probed values will not be saved from a canceled probing sequence.

Z Offset Calibration

Once probing is completed, the tool will move to the center of the probed area. You will see that the nozzle will move very close or possibly touch the bed. At this point, you will use the Tool Adjustment Distance and Adjust Printing buttons to adjust the Z offset and set the zero point for the Z-axis.

Tool Adjustment Distance

Select the distance to adjust the Z offset. Pressing this will not trigger a modification of the offset.

Adjust Printing

The Adjust Printing buttons will adjust the Z offset of the active toolhead, moving the bed farther or closer to the nozzle according to the selected Tool Adjustment Distance. This command is executed instantly. Modify the Z offset so that the nozzle is just barely touching the bed.

Once the initial calibration is complete, you may switch tools, and repeat the process for the opposite tool if required.


After you have probed the bed and done a rough calibration, the distance from the nozzle to the bed will be nearly calibrated, but not as precise as required for printing perfect first layers. This can be fine-tuned while printing your first layer by making further adjustments to get the initial spacing correct. It is for this reason that we recommend always printing parts with a brim, skirt, or raft that may be treated as sacrificial.

Before Printing

Once all probing has been completed, use the jog controls in the Motion tab under the control menu in the user interface to move both tools off the build platform.

Raise the temperature back up to the extrusion temperature required for the material being printed.

Re-extrude the 20mm of filament you retracted earlier.

If you are printing with both toolheads on the same model (ex. using T0 to print the model and T1 to print its support structure), you will also need to calibrate the toolheads in X and Y before printing your part. This procedure shifts the coordinate system of T1 to line up with T0, so the original mesh you got from probing with T1 will no longer be accurate and you will need to probe the bed again with T1 before printing. You can find instructions and more information in the X and Y Tool Calibration procedure under the Calibration section.

AON3D recommends probing the bed before every print, especially if you have changed the printing temperatures or made physical changes to the machine, including changing nozzles, repairing toolheads, or swapping build surfaces. You may have to fine-tune the offset again when printing at different temperatures and after making changes to the machine.

Printing Your First Layer

While the initial calibration will bring the nozzle-bed distance close to its ideal, you will still need to manually fine tune the offsets on each print while extruding a sacrificial skirt or brim for the first layer. Once calibrated, this should only require very small changes to account for minor deviations in machine dimensions that accompany changes in machine temperature due to thermal expansion.

To learn more about printing a good first layer and to practice fine-tuning the Z offset, see the First Layer article in the Operation section.

Last modified: February 13, 2020