BlTouch Ender 3 V2 - nozzle always low, even when Z-Offset is set higher than bed

I recently purchased an AntClabs BlTouch sensor from 3D Printing Canada, and it has become a major source of frustration for me for the past day.

I first started with installing Jyers Fork of Marlin Firmware and tried to tune the BlTouch via the Z-Offset. I made sure my GCode add line G29 after G28 before I started my print. I made sure the bed was level, and that a Piece of paper was snug against the nozzle beforehand. I press print… and the nozzle was too low, causing a clog and scratching my bed.

I played around with it some more with it resulting in more failures. I then made the decision to flash Creality’s fork of Marlin for the BlTouch. Tried again, tried my best to tune the Z-Offset, resliced the file for good measure, and same issue.

While playing around with it, I noticed that even when I set the Z-Offset to where the paper was not snug against the nozzle, the printer would still send the nozzle low into the bed.

If anyone has any suggestions that would be very appreciated!

Why are you using paper with a BL touch? The BL touch sensor up should be (correction) 2.3-4.3 mm above the bed.

There are a number of BL touch cal targets. Basically you start so the point of the touch is above the bed and let it probe down. They you adjust the height with baby stepping in the menus.

I’m using a piece of paper only because that’s what I’ve seen recommended on tutorials online. I’ve seen a BlTouch spacer - but never this, in theory could both solve my issue?

Don’t use paper. That is a kludge system for manual bed levelling. Get the bed as accurate as you can then set up the bl touch and only here and there will you need to ‘level’ Tram the bed.

This might help

First off, I don’t have a BL Touch, but hopefully I’m grasping the problem well enough to provide a meaningful reply. If I’m wrong, someone chime in and correct me, please.

Z-Offset only comes into play AFTER the print head has been homed on the Z-Axis. On a printer without a BL Touch, the printer will perform the homing function by bringing the bed and nozzle together until the Z-Axis limit switch is triggered. Only then will it back off a distance equal to the Z-Offset. If the nozzle impacts the bed, it means the Z-Axis limit switch is not being triggered early enough. On my Ender 5 Pro, this is set by a thumb screw at the back of the bed that you can raise and lower in order to trigger the limit switch just as the nozzle touches the bed.

When you state that the nozzle is being sent “low into the bed”, I’m interpreting that to mean it is impacting it.

On a BL Touch, you aren’t using the Z-Axis limit switch. The BL Touch probe is supposed to do that job. It suggests to me that there are three possibilities:

  1. you either don’t have the firmware set up to use the BL Touch as a limit switch having, presumably disconnected the Z-Axis limit switch as part of the BL Touch installation.
  2. the BL Touch is not wired properly to send the signal to the controller to indicate that the probe has been triggered.
  3. there is a remote possibility that you have the Z-Offset set negative. That is; when the probe is triggered, the printer tries to move the nozzle down instead of up.

Both 1 and 2 I’ve confirmed are not being at play - however, I do set my Z-Offset to a negative. It is from what I’ve learned required so the firmware knows how much it needs to move the nozzle down. So it should go like this:

  1. Probe,
  2. Bring nozzle down towards bed
  3. Print
    However when it brings the nozzle down towards the bed, it is way too low - I’m trying Kitedemons 3D print later tonight, hopefully that’ll help solve the issue

Your Zero point is the point at which the limit switch or BL touch are triggered and it should be the point where the nozzle just touches the bed (ie. you are 0 mm above the bed). The Z-Offset is offset from Zero and so must be a positive number.

Remember, there’s no point in having a negative Z-Offset. When you’re BL Touch pin gets pushed in or when a non-BL Touch printer hits it’s Z-Axis homing switch, it means the switch has been physically impacted. That’s why it’s called a “limit” switch - it’s as far as you can move. Any further and you risk damaging something.

Change your offset to a positive number.

By the way, in case you’re wondering why it’s even possible to have a negative Z-Offset; there are “limit switches” (sensors actually) that are optical. They consist of an infra-red transmitter and an infra-red receiver and are triggered when something passes between them. No actual collision is involved so it’s technically possible to enter negative territory without doing damage.

Ender 3, Ender 5 and BL Touch are all impact-type sensors and as such, you can’t go past them (negative values) without risking damage.