Every 3D printing enthusiast who has utilized automatic bed leveling knows how much of an impact it has on the printing process, both in terms of the consistency and accuracy benefits it brings to the print and the quality of life benefits it brings to the user.
On the other hand, similar to many other things, the automatic bed leveling process is not entirely automatic or flawless either since it relies on the configuration we provide it to function correctly, which makes room for problems to occur in the case of a misconfiguration.
Today, we will be examining the widely encountered issue of the 3D printer nozzle hitting the bed during the auto-home process or the printing process itself while utilizing the BLTouch auto bed leveling sensor, a critical problem that requires resolving as soon as possible due to the damage it can cause.
So, what can cause the nozzle of your 3D printer to crash into the bed while printing or homing with the BLTouch auto bed leveling sensor?
The primary reason that will cause the nozzle of your 3D printer to crash into the bed while using the BLTouch is an incorrectly set Z Probe Offset value, which is what the 3D printer uses to calculate the difference between the BLTouch and the nozzle.
In the upcoming parts of the article, we will dive deeper into what can cause the nozzle to hit the bed while using the BLTouch sensor, find out how to fix the problem as optimally as possible, and take a quick look at a specific scenario, where the BLTouch probe is positioned too high above the nozzle.
What Can Cause the Nozzle to Hit the Bed While Using BLTouch?
The nozzle hitting the bed is a scenario that can be damaging to both the bed and the nozzle itself, which is why it’s essential to identify the root cause behind the problem as quickly as possible before trying to print again.
A Z Probe Offset that is not configured correctly is the most common culprit behind the nozzle of your 3D printer hitting the bed while automatically leveling your bed with the BLTouch sensor.
In a nutshell, the Z Probe Offset value is the distance that the 3D printer will use to lower the nozzle after the BLTouch makes contact with the bed, essentially meaning that this value will always equal the distance between the nozzle and the tip of the BLTouch push-pin at the trigger point.
When this value is incorrect, the 3D printer has no way of knowing how far up the nozzle is positioned compared to the tip of the BLTouch pin, meaning that in cases where this value tells the 3D printer to lower the printhead a greater distance than required, the nozzle will end up crashing into the bed.
How to Fix the Problem of the Nozzle Hitting the Bed While Using BLTouch?
While the process of applying the necessary solution to prevent the nozzle from hitting the bed is a straightforward one, it does require some focus to ensure that you are getting the value correct, which will determine whether the nozzle will keep hitting the bed or not.
To fix the problem of the nozzle hitting the bed while using the BLTouch, you will need to configure the Probe Z offset value correctly, which you can conduct in a few different ways:
- M851 G-Code – The M851 G-code allows you to directly set the X, Y, and Z probe offset values, which you can send to your 3D printer by using a 3D printing interface software such as OctoPrint or Pronterface. In most cases, it should also be possible to find this option on the LCD panel of your 3D printer, such as the Probe Z Offset option in the Ender 3.
- Probe Offset Wizard – The Probe Offset Wizard is an optional Marlin firmware feature that, when activated, creates a new entry on the LCD panel that merges the process of moving the printhead in the Z position and saving the probe Z offset into one.
- Firmware Modification – It’s possible to directly hardcode the probe Z offset values to the firmware configuration if you wish to, but these values will be overridden by any changes you make through the above options.
- Babystepping – Babystepping is a feature that allows you to tune the probe Z offset value in real-time during the printing process, with its primary purpose being to perform fine adjustments that will only apply to a particular print.
While the methods we have specified above are exclusively for the Marlin firmware, it should be possible to find similar functionality for any popular 3D printer firmware by referring to the documentation.
The BLTouch Probe is Too High Above the Nozzle – What to Do?
The BLTouch probe being positioned way too high above the nozzle is a specific scenario that will always cause the nozzle to hit the bed, as the BLTouch will try to lower the printhead all the time due to it thinking that the build plate is not in reach yet.
Mounting the BLTouch at a position where it’s way too high above the nozzle will make it impossible for the sensor to detect the bed, which will always result in the nozzle crashing into the bed as the BLTouch keeps lowering the printhead to find the bed.
To fix the issue, you will need to re-mount the BLTouch at a position where the distance between the tip of the BLTouch case and the tip of the nozzle falls into the range of 8 to 8.5 millimeters, which will ensure that you won’t have problems with the probe being too high above the nozzle again.
For the best results, we highly recommend measuring the distance with calipers, which will ensure that your measurements are exact and without any error, as even an error of a few millimeters can cause the issue of the nozzle hitting the bed.
The nozzle of your 3D printer crashing into the bed is definitely something you would want to avoid due to the potential damage that can be caused by such a scenario, which is why we highly recommend ensuring that everything is in order before moving on to the printing process again.
To quickly recap, a misconfigured Z Probe Offset value is the first factor that comes to mind if the nozzle of your 3D printer is crashing into the bed while using the BLTouch, as such a scenario will prevent the 3D printer from knowing the correct position of the nozzle relative to the BLTouch.
As you will need to configure the Z Probe Offset precisely to avoid such as situation, or the exact opposite where the nozzle hangs in the air after automatically leveling the bed instead, we highly recommend taking your time with it to be on the safe side.
Mike started his 3D printing journey with the Anet A8 when it first came out back in 2017, and has been obsessed with 3D printers ever since. Nowadays, he primarily uses his Ender 3 to print functional parts that make his life more convenient whenever possible.