Automatic bed leveling is quite a common feature in consumer FDM 3D printers in 2019. Most machines with auto-leveling, however, use a contactless inductive sensor which is simple to install, operate, and configure. These inductive probes work well with a metal build plate, but build platforms made of other common materials, such as glass, are practically invisible to inductive sensors.
That might have been the way BLTouch sensors came onto your radar: If you need to use a non-metal bed but also want auto-leveling, these sensors are an accurate option. Or maybe accuracy was your prime concern. After all, the original BLTouch readings have one of the lowest standard deviations of all auto-leveling sensor types.
So without further ado, let’s break down the BLTouch probe and show you all you need to know about this contactless auto-leveling sensor.
According to Antclabs, the maker of the probe, “BLTouch is an auto leveling sensor for 3D Printers that can precisely measure the tilt of (sic) bed surface.” This sensor works on any type of bed surface, be it metal, glass, wood, etc.
The sensor itself is fairly complex as bed sensors go. It consists of a microcontroller, a solenoid switch, and a push pin 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 push pin, 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 controlled by a servo motor. When the toolhead lowers to home the nozzle in the Z-axis, the pushpin triggers the hall sensor, at which point the pushpin retracts and the toolhead raises.
In terms of accuracy, the BLTouch is on par with optical endstops which trigger using light.
Let’s compare the BLTouch to other common bed leveling sensors:
The key difference between an inductive probe and the BLTouch is that one sensor physically touches the bed in the leveling process. (Hint: It’s not the inductive probe.) The inductive probe uses currents induced by magnetic fields to detect metal objects nearby, eliminating the need to physically touch the bed in order to sense it. But therein lies the problem: Inductive sensors only work on metal beds, since they’re only capable of triggering when in contact with metal. This might be a deal breaker if glass is your preferred bed material.
Microswitch (Physical Endstop)
Let’s not discount the old-fashioned physical microswitch. Compared to the BLTouch, this option is less accurate and possibly less reliable in the long term, since the sensing depends on physical components which can wear over time (at least for the physical switches found on most FDM machines). However, these physical switches give the other fancier sensors a run for their money in the cost and ease of configuration department. Since physical switches are the simplest and earliest form of Z-homing sensors, they’re easy to obtain and trivial to set up.
An optical endstop functions with the use of light, which has made it impractical for many new machines that end up being hybrids. After all, milling wood blocks with a spindle tends to put out some dust in the air. In addition, these sensors are impractical for many entry-level machines due to their more complex wiring and firmware setup. In the small number of applications where they are practical, though, their accuracy is equal to that of the BLTouch.
The setup process for this probe varies by machine, but here are the general steps:
Make sure to look for a BLTouch setup guide for your specific machine just in case there are some special configuration steps for your hardware.
There are a couple of sources you can buy the original BLTouch auto-leveling sensor from, as you can see below.
If you can’t quite afford a genuine BLTouch, try other sensor types such as the ubiquitous inductive probe or the good old-fashioned microswitch, for example.
License: The text of "2019 BLTouch Sensors Guide – All You Need to Know" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.