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AON-M2 Machine Calibration


The information on this page is for firmware version 18.08 and newer. If you are unsure of what firmware version you are using, please verify that you are using version 18.08 or newer with the command M115 before proceeding. To update firmware, see this guide.

Bed Leveling

The AON-M2 uses active bed leveling while printing to compensate for any irregularities that may occur in the bed surface. This is especially critical when repeatedly cycling the plates from room temperature up to 200ºC and back again which can cause slight warping and deformation of the plate surface. The bed-probing process should be run every time your printer may undergo changes in dimensionality. This includes but isn't limited to:

  • print-plate changes
  • nozzle changes
  • significant temperature changes (> 10ºC)
  • machine relocation

AON3D recommends probing the bed before every print, however if you are running multiple prints consecutively without significant changes to the bed or tools, you may find it unnecessary to probe again.


If using both toolheads, you will need to probe the bed using both. This prevents any error that may exist on one tool from influencing the other, as well as ensuring that if one tool is out of service, the other can function normally.

The M2 compensates for bed irregularities by using a 25 point topographic mesh and tool probe offsets to compute a value that is then applied to the machine's Z position ensuring that the tool is always the correct distance away from the bed surface. When printing parts that need to be geometrically precise, this can introduce error as the bed topography is inherently transferred onto the part. To combat this, the bed leveling compensation is faded out gradually in the first few layers of a print to minimize the effect. The process is as follows.

Probing a Mesh

Each tool has its own mesh and probe offset and should be treated as an independent calibration. By default, meshes are set to 20mm at all points, and the probe offset is 3mm. This in effect results in the bed having a zero point 23mm below the z-endstops.


These default values are only present until overwritten! Once you have probed the bed, the mesh will be saved to the last recorded values.

Preheat your bed and chamber to the desired printing temperatures and wait for the machine to reach a steady state. Home the machine with the G28 command. Once preheated, run the command G29 in the terminal with the desired tool active. This will initiate the probing sequence. Once completed, the tool will return to its respective "home corner" (i.e., the front left for the left tool, and the front right for the right tool).

You will see that the nozzle will move very close or possibly touch the bed. To correct this and "touch off", use the command M290 Znnn to modify the probe-offset so that the nozzle is just barely touching the bed. Please note, this must be done at the operating temperature for the material you intend to print.

For example, the command

M290 Z0.1

will move the bed 0.1mm away from the nozzle, while

M290 Z-0.2

will move the bed 0.2mm closer to the nozzle.


In the terminal page of the user interface, you can use the up and down arrows on your keyboard to quickly cycle through past commands.

Once the initial calibration is complete, you may switch tools, and repeat the process for the opposite tool if required. It is important to note that this is only a rough calibration, and small adjustments will likely be necessary when printing your first layer. It is for this reason that we recommend always printing parts with a brim, skirt, or raft that may be treated as a sacrificial.

Once all probing has been completed, run the command G28 X to move both tools to their parked positions.

Probing with "High Temperature Build Plates"

If you are using a PEI Plate bed (not PEI Film, but ¼ inch plate), the probing process has a few additional steps and precautions that must be taken.

Preheat Time

Because PEI has a much lower thermal conductivity than aluminum, it is necessary to wait for at least 30 minutes once the bed has reached its target temperature on-screen. This will allow for the plate to fully expand and reach the desired temperature before probing.

Nozzle Temperature

Probing on a PEI Plate requires lowering hot-end temperature so as not to damage the plate. We recommend lowering the hot-end temperature to 200ºC, then once probing and calibration is complete and the tool has been moved to its parked position, raise the temperature back up to the extrusion temperature required for the material being printed.

Filament Retraction

Before probing, make sure the filament has been removed from the "meltzone" of the hot end. This can be done by heating to the material's operating temperature, extruding until material is extruded, 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.

Printing - "On the fly adjustment"

Once you have probed the bed and calibrated the offsets, you may run a print.

While printing the first layer, you will need to fine-tune the probe offset value by sending more M290 commands to the printer to adjust the bed-to-nozzle distance to get the appropriate distance. Once this has been done, only minor adjustments should need to be made for future prints (typically +- 0.1mm).