Probing fail // BL touch

Hi all,

I've been struggling this week with our BL touch.
It gets some way through the bed levelling process and then stops with the message 'probing failed'.
Watching it as it happens, the probe lowers but doesn't quite touch the bed resulting in the error and then the BL Touch starts it's error flash sequence.

This began happening every 4th or 5th attempt, but its become progressively worse until now it happens every time and I can't get a print started.

I spoke with the guys at gCreate about this before as we've had this same issue in the past, however all the tips they gave last time aren't working this time so thought i'd cast the search a little wider to see if anyone else has had any luck and could advise.

For reference:
- I've removed the BL Touch and inspected to make sure there are no obstructions.
- I've checked all the wiring looms to make sure they are plugged in correctly and aren't compromised in any way.
- Reset the machine.
- Cleaned down all moving components to make sure there are no obstructions to movement that might be causing the error.



Staff member
Try uploading the firmware again. I have seen this happen on one of our print farm printers. Uploading the firmware basically reset the z-offset. Or reset anything you may have accidentally turned on or off in the settings.
By this do I understand you to mean levelling the rail on which the print head is fitted (running left to right) to the bed?
Yes. If it is far enough out on one side, the probe won't touch the bed. This happens to me if I am working on the printer with the power off and put pressure on the x rail. The z screws move easily when the power is off.
Have you tried measuring the distance between the x axis (the rail on which the print head moves left to right) and the print bed ?
You need to measure on the left and right side of the axis and ensure they are the same value. If not, adjust the z lead screw manually (turn it), measure again, and repeat so long as the measurements are different.

Also, when you select the "Raise Z Axis 100mm" in the menu, does the z axis move up smoothly? Ensure that the Z coupler and Z lead screw holder are properly secured on the machine. Also, check that while the Z axis moves up during the command, the z lead screws aren't moving side to side. While testing this, remember to lower the Z axis each time.

If none of this helps, I would go through the guides for maintaining your 3d printer in this forum and ensure everything is okay.

It could be that your wheels on one side of your printer are not properly turning inside of the v-slots (check this by trying to turn the z axis wheels (on the left and right side of the printer). If they turn easily without moving the axis, they need to be tightened until you cannot move them with your hand. Be careful that they are not over tightened as well, as that can prevent one side from raising with the other.
Thanks for the advice.
I check how level the x axis rail is fairly regularly using a spirit level rested on top coupled with using a datum block to measure the distance between the rail and bed on the left and right side.
When doing this occasionally I find that the distance between the rail and bed (left and right) is equal but the spirit level is slightly off, indicating the bed itself is angled. I take this to be the construction of the printer becoming loose overtime and therefore nuts and connectors etc need to be tightened and maintained regularly as you suggest.

When raising the Z axis there is a bit of reverberation in the rig, but the actual movement of the arm is quite smooth.

The predominant issue i find is that during one print, it all levels up and the layers are equal across the bed yet on the next it might be unequal (layer flattened on one side, beaded on the other) and requires being turned off and reset. This indicates that it might be a firmware / software / gcode issue, hence why I put the question out to see if others have seen this problem.
As Joshua says above, I will try reinstalling the firmware and hopefully it will help.