Several months ago I wrote an in-depth article on How to Setup Auto Bed Leveling which covered the entire process from start to finish… at least almost. As this was my first time using Auto Bed Leveling on my 3D printers, I was still testing out various methods to properly calibrate the sensor and opted to exclude this part from the guide. Nothing I had tested up to that point worked as expected and every print job embedded plastic in to the build surface, to the point I ended up having to replace it several times.

After I grew tired of using a wrench to knock prints off the bed, I found a video from 3D Maker Noob that looked promising. Rather than try to adjust the sensor’s position by hand, we could use g-code commands to calibrate it with ease. Go figure, it took all of 5 minutes and my auto Bed Leveling sensor was near perfect.

Most of this guide will just reiterate the information he provides in the video, but several personal observations have been added as well. Once you understand it, auto bed leveling makes perfect sense, but most of the resources found online are either needlessly complicated or just plain wrong.

Calibrate Software

Before we can get started, we first need to grab some software that can communicate with the 3D Printer over USB. While most slicers have this feature built-in, Cura seems to be the rare exception that lacks direct machine commands (despite otherwise being complete printing solution). There are however several other tools I have linked below that will work just fine for our needs, where I would suggest Pronterface based on the simple, easy to use interface.

Pronterface
Repetier Host

As a third option, Simplify3D ($149) is exceptional software and my preferred slicer software of choice. It is however quite expensive and not worth the price tag for the average person, so unless you already own it, one of the free solutions above will be more than capable of getting the job done.

Instructions

If you haven’t done so already, go ahead and connect the 3D Printer to your computer using a USB cable and power it on. Start up Pronterface (or whatever software you decide to use) and connect it to the machine. The Baud Rate will likely be set to the default of 115200 and the COM port will appear when the 3D Printer is connected, such as COM3.

Step 1: Clear Out Z-Offset

Since there might already be a z-offset configured in the firmware or EEPROM, we will start by clearing out any existing values and reset the offset to 0.00.

G28 Home the nozzle
M851 Z0 Set the z-offset to zero
M500 Store the settings to EEPROM
M501 Load the settings from EEPROM
M851 Echo the current z-offset value, make sure this reports Z0

Step 2: Move to Actual Z-Offset

When the Auto Bed Leveling (ABL) sensor is triggered, the firmware will raise the nozzle up by several millimeters. Since we want to work from the actual 0 z-offset, we need to reposition it at the point the sensor was triggered. To do this, we will use G1 F60 Z0, where G1 is the move command, F60 is the travel speed, and Z0 is where we are moving to.

G28 Z Home the nozzle on the Z axis
G1 F60 Z0 Move the nozzle down to the actual 0 offset

Step 3: Calibrate Z-Offset

Just like we are used to with manual bed leveling, go ahead and insert a piece of paper under the nozzle to test the distance. Using the movement controls in the software, start lowering the nozzle towards the build plate in increments of -0.1mm, until there is a slight drag on the paper when sliding it underneath. We will temporarily disable the software endstops, where that will allow us to go in to negative values on the Z axis while we calibrate the proper offset.

Once you are satisfied with the distance between the nozzle and the bed, make a note of the z-offset on the 3D Printer’s LCD screen, which should look something like “Z-0.5”. Now add the thickness of the paper you used to this value and that is your actual z-offset.

Note: A normal sheet of paper has an average thickness of 0.08mm. If your LCD screen reads Z-0.5, we would configure this as Z-0.58.

M211 S0 Turn OFF the Software Endstops
M851 Z-0.58 Set the z-offset value
M211 S1 Turn ON the Software Endstops
M500 Store the settings to EEPROM
M501 Load the settings from EEPROM

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