Z Calibration

This instruction set reflects improvements added in software application version 3.0.4. In the Settings menu of the user interface, check the Updates tab to make sure your software is up-to-date. You can find instructions to update the software in the Maintenance section, under Software Update

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.

  1. In the Temperature menu of the user interface, enter the bed and chamber temperatures you will use to print.
  2. 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.

  1. In the Temperature menu of the user interface, enter the extrusion temperature of the material loaded in your hot end.
  2. Once the tool has reached the extrusion temperature, navigate to the Motion tab of the Control menu. Make sure the correct toolhead is selected.
  3. Select 10 for the Extrusion Distance. Extrude filament until material begins to come out of the nozzle.
  4. Retract 20 mm of filament by tapping Retract twice.

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.

  1. Lower the hot end temperature to 200ºC.

In order to protect from damage during probing, changing the hot end temperature is blocked during the probing process.

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

Set the Probe Bounds

If you are not using the entire build surface, you can choose a smaller section to probe. The preview shows the points that will be probed within your chosen bounds. The black dots are probe points and the blue lines are the boundaries of the defined probing area. The red dots show the position of the bolts on the High Temperature Build Plate.

Probe Bounds and preview in the Z Calibration tab

  1. Determine the bounds of your printing area using the Print Preview in the Simplify3D software. In the left toolbar of the Print Preview, under “Show in Preview”, select “Build table” to show the build area grid lines.
  2. Enter these limit values in the Probe Bounds (Left/Right and Front/Rear). The number is the distance in millimetres relative to the (0,0) origin located at the front left corner of the build platform. The probing area must be at least 30 x 30 mm.
  3. The preview will automaticaly update to show the area you have selected.
  4. The X and Y Counts are the number of points equally distanced on each axis that will be used to build the probing grid. Enter the number of points you want to probe. You must probe at least three (3) points in each axis.

    A higher count adds more definition to the grid. A lower count reduces the time it takes to probe the bed.

Restrictions on Probe Bounds are summarized below.

Probe Bound Default Value Minimum Maximum
Left 35 0 Right - 30
Right 415 Left + 30 450
X Count 8 3 10
Front 35 0 Rear - 30
Rear 415 Front + 30 450
Y Count 8 3 10

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

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.

Probe the Bed

  1. Use the Tool Select buttons to select the tool you want to probe with.

    Tool Select and Probing buttons in the Z Calibration tab

    If you will be using both toolheads on the same print, you will need to probe your print area with both toolheads.

  2. Tap Start to initiate the probing sequence for the selected tool.

  3. The machine will home the axes and proceed to probe the bed. Each point in the probing grid will be measured several times. Watch the first few probe points to make sure the probe is moving smoothly.

    If the machine has difficulty compressing the probe, or if the probe gets stuck in the compressed state, you may have forgotten to retract the filament. Tap Stop to stop the probing sequence and follow the instructions above to retract the filament before initiating the probing procedure again.


You can tap Stop at any point in the probing procedure to cancel it. This stops the probing sequence and the active toolhead will go back to its initial X position.

Probed values are reset to the default configuration (30 mm) when probing is stopped. If you stopped the sequence because you did not intend to probe the bed, you can use M501 to retrieve the values from the last successful 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. A rough calibration is done before printing. This will be fine-tuned while printing your first layer.

Offset Adjustment buttons in the Z Calibration tab

  1. Use the Tool Adjustment Distance buttons to select the distance to adjust the Z offset. Pressing this will not trigger a modification of the offset. For this rough calibration step, use the 0.1mm and 0.05mm distances.
  2. Tap Farther or Closer to adjust the distance from the bed to the nozzle. This command is executed instantly.
    Farther will move the bed down by the selected Tool Adjustment Distance.
    Closer will move the bed up.
  3. Modify the Z offset so that the nozzle is just barely touching the bed, or just above.

    Make sure the probe is not compressed at this point. This can happen if you adjust the offset too close. For this rough calibration step, it is better to leave a small gap between the nozzle and bed than push them too close. This avoids the risk of collisions, or having the nozzle scrape the bed.

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

Before Printing

Once the machine is probed, do not home again before printing as this can introduce error in the calibration.

  1. 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.
  2. Raise the temperature back up to the extrusion temperature required for the material being printed.
  3. Re-extrude the 20 mm of filament you retracted earlier.
  4. 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

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 extruding a sacrificial skirt or brim for the first layer.

  1. Set up your print with a brim, skirt, or raft that may be treated as sacrificial. These settings can be found in the Additions tab in Simplify3D.

    All FFF profiles provided by AON3D are pre-set with sacrificial additions for fine-tuning the offset. You can find FFF profiles in the Materials section.

  2. Use the 0.05 mm and 0.01 mm distances to adjust the offset at the start of your print.

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. For new users, we recommend running the fine-tuning practice print before each new print. This is also a useful excercise when switching to a new nozzle size or new material for the first time.

Last modified: July 7, 2020