According to Antclabs, the Korean manufacturer of the probe: “BLTouch is an auto-levelling sensor for 3D printers that can precisely measure the tilt of a bed surface.” This sensor works on any type of bed surface, be it metal, glass, wood, or something else entirely. That is probably how you first found out about BLTouch sensors. If you need to use a non-metal bed like glass but also want auto-levelling, these sensors are a great option. You also could have thought about adding one for its accuracy. After all, the original BLTouch readings have one of the lowest standard deviations of all auto-levelling sensor types. Without further ado, let’s break down the BLTouch probe and show you all you need to know about this contact-based auto-levelling sensor.
The sensor itself is fairly complex as far as bed sensors go. It consists of a microcontroller, a solenoid switch, and a pushpin probe which comes into contact with the bed. The original BLTouch uses a hall sensor for high accuracy, and this sensor, in conjunction with the physical pushpin, is what allows it to be used with many bed types. In a sense, this sensor is equivalent to a microswitch, mounted on a servo arm, and controlled by a servo motor. When the tool head lowers to “home” the nozzle in the Z-axis, the bed pushes the pushpin slightly upwards, triggering the hall sensor, at which point the pushpin retracts and the tool head raises.
The BLTouch is one of the most accurate and reliable sensors available, so it’s no surprise that a few manufacturers such as MakerGear and CraftBot use this device on their high-end machines.
General Setup: Mounting the Probe
The BLTouch probe will need to be mounted as close to the print head as possible. You can find many designs available for you to download directly, or if you’re in the mood to design one on your own, make sure to read the BLTouch documentation to get the correct measurements. Some users run into an issue where the nozzle digs into the bed on one side and print perfectly on the other. The reason that this happens is that the BLTouch is mounted at an angle with respect to the nozzle.
So, when designing and mounting your hardware, make sure to have the BLTouch mounted perfectly square and aligned with the nozzle. Once you’ve mounted the probe, make sure to note the distance between the probe of the BLTouch and the centre of the nozzle in both the X and Y directions.
To get the BLTouch up and running, the printer’s firmware will need to be modified in a few places such as the servo angles, but all of this as available on the Antclabs website.
Once the firmware settings are dialled in, you’ll need to check if the BLTouch is working as intended by running a basic test. Once that’s completed, you can get started with adjusting your Z-offset. There’s a great video by 3DMakerNoob that takes you through the entire process step-by-step. Configuring the Slicer Make sure to add a G29 command in your start G-code, right after the G28 command, as shown above.