Prusa XL 5 Head failing Z-Axis Test and Tool Offset Calibration
I have just recently set-up the Prusa XL with the 5 tool heads last week. The setup went smoothly however the printer has been failing the z-axis test and tool offset calibration tests. The z-axis test had failed several times and then all of a sudden the test passed without me making any adjustments to the printer. After re-running the test it has randomly failed and passed numerous times and I've not been able to identify what is allowing it to pass or causing it to fail - the test gives no information, just pass or fail.
The tool offset calibration has yet to pass after multiple attempts. The calibration fails during the first tool calibration and I have swapped over the extruder head so that the calibration starts by using a different extruder to check if it was a problem with the extruder but the test still failed at the exact same spot as all prior tests. I have also re-run all prior calibrations which have all passed but when it comes to the tool offset calibration it has always failed in the same spot and comes up with the error message attached.
Has anyone had similar issues that could share some advice?
Best Answer by OverServed:
I faced a similar problem and spent a month troubleshooting it with tech support. Ultimately, it was discovered that the core XY was not locked in place properly. The Z-axis extrusion pins need to be properly locked in place in the holes in the base and the core XY. It would seem obvious, but the pins can shift slightly out of their holes when being assembled and still be tightened down. It was a stupid mistake on my part, but was obvious when I reassembled the printer. Works like a champ now. Super pleased with the print quality. Note of caution: put the Z-axis bearing stops in before disassembly to avoid losing bearings.
RE: Prusa XL 5 Head failing Z-Axis Test and Tool Offset Calibration
I faced a similar problem and spent a month troubleshooting it with tech support. Ultimately, it was discovered that the core XY was not locked in place properly. The Z-axis extrusion pins need to be properly locked in place in the holes in the base and the core XY. It would seem obvious, but the pins can shift slightly out of their holes when being assembled and still be tightened down. It was a stupid mistake on my part, but was obvious when I reassembled the printer. Works like a champ now. Super pleased with the print quality. Note of caution: put the Z-axis bearing stops in before disassembly to avoid losing bearings.
RE: Prusa XL 5 Head failing Z-Axis Test and Tool Offset Calibration
Thanks for your response. I have just noticed a notable gap between the top of the z-axis extrusion and the core XY frame. I have attached some images, would you be able to say if this looked similar to what you had seen on your printer? Just before I begin disassembling. Also, do I need to disassemble the back plate and extruders before I try take off then re-attach the core XY, or can I just undo whatever is holding down the core XY and re-jig it to remove the gap and then fasten down again?
RE: Prusa XL 5 Head failing Z-Axis Test and Tool Offset Calibration
Thanks for your response. I have just noticed a notable gap between the top of the z-axis extrusion and the core XY frame. I have attached some images, would you be able to say if this looked similar to what you had seen on your printer? Just before I begin disassembling. Also, do I need to disassemble the back plate and extruders before I try take off then re-attach the core XY, or can I just undo whatever is holding down the core XY and re-jig it to remove the gap and then fasten down again?
Good gracious, that's not right. The surfaces should have zero gap and torqued together tightly. The bump on the vertical extrusion should be entirely within the groove of the horizontal extrusion. It's a tight fit and you need to "wiggle it" together before torquing down the bolts.
I would personally disassemble. Lowers the risk of damaging nearby parts.
RE: Prusa XL 5 Head failing Z-Axis Test and Tool Offset Calibration
That looks like the same issue that I faced. There shouldn't be any gap between the extrusions when done correctly. The pegs won't be visible.
I had to disassemble most of the printer, especially the back/side plates and the cabling, to maneuver the core XY. I took off the toolheads from their pegs and disconnected the cables. It will probably depend on your workspace and whether you have a second set of hands to help. I decided to take most of it apart and organize the parts/fasteners in small bags to keep everything organized to go back together. It's a pain, but it's worth it in the end. Good luck!
RE: Prusa XL 5 Head failing Z-Axis Test and Tool Offset Calibration
Thank you for the responses @mikeo-2 & @nhand42. I was able to disassemble the side enclosure panels and both electronics covers on the back plate. This was all that was needed to access the screws to free up the core XY. From here I re-jigged the core XY to fit better on the pins, at this point there was still a gap between vertical extrusions and core XY extrusions. Upon torquing up the screws this gap was closed.
The setup instructions note that a small gap can be expected at the stage of installing the core XY onto the vertical extrusions and the gap will be addressed in a later step. The instructions do not mention anything about ensuring the gap closes. I have placed a comment at that stage of the setup regarding this.
RE:
Is this an acceptable degree of separation? I've stripped 25 screws, had to grind down 3 hex heys about 10 times and this is as far as I can get as I now have one of the screws permanently stuck in the frame. 
RE: Prusa XL 5 Head failing Z-Axis Test and Tool Offset Calibration
These pictures helped me soooo much. Once I eliminated the gap calibration ran perfectly. Relieved to know I wasn't the only one that missed this detail on assembly. Thanks for sharing. Happy printing.
RE: Prusa XL 5 Head failing Z-Axis Test and Tool Offset Calibration
Similar, situation here, while the z calibration would work on and off - different heads would fail the calibration. Looking that the photos was epic and I was able to see a small gap on either side - great fun taking apart what I just put together 🙂 but the end result was no gap and full calibration success. Thank all for the assist.
RE: Prusa XL 5 Head failing Z-Axis Test and Tool Offset Calibration
Like I wrote in my thread I have the same problem with my new factory assembled XL failing the offset calibration. Just checked, but I have no such gaps. Spend several hours yesterday with support trying all kind of things with finally doing a factory reset and flashing the firmware and start calibration all over again. Didn't help. Running out of options they suspected the motherboard and offered to send me a new one.
They offered to send it back to the factory for repair or refund too. Sad to say, but I will take the refund. The prusa experience wasn't what I expected! Paying almost 5000 Euros for getting a machine that doesn't work just should not happen. I am very frustrated (and angry) spending 2 days building this machine and taking it apart again just to send it back. Waste of my time.
The only good thing: The support operators were always very helpfull and friendly.
RE: Prusa XL 5 Head failing Z-Axis Test and Tool Offset Calibration
Hello!
I had this issue myself and noticed the nozzle wasn't touching the calibration pin at some points. I redid the X and Y calibrations first, and then had no more issue with the Tool Offset Calibration. Hope this helps someone else!
RE: Prusa XL 5 Head failing Z-Axis Test and Tool Offset Calibration
How do you "re-jig" it to get the vertical extrusion bump to fit into the grooves properly? I'm in the process of attaching the CoreXY to the extrusions and none of the extrusions are completely seated. I put in the screws, and maneuvered it to sit upright. I was hoping that tightening the screws up would cause the extrusions to pop into place, but I tried on one and that did not occur.
So now I've removed the screws, put it back on its side, and reseated the whole CoreXY. Still not lining up. Do I need a second set of hands? Do I need to use more force on the extrusions?
Do I need to also loosen the torqued screws that are securing the extrusions to the base, so I get some wobble in the extrusions?
How do I get all 4 bumps to fit into the grooves properly so I can eliminate the gap?
RE: Prusa XL 5 Head failing Z-Axis Test and Tool Offset Calibration
I found it easier to mount the top frame while the unit it upside down.
Mind you though that you need to add some wooden pieces or other blocks below the frame as the gantry the toolhead mounts to need to have it's room below the frame.
RE: Prusa XL 5 Head failing Z-Axis Test and Tool Offset Calibration
Ha, brilliant!
I found that I was able to tighten it up sufficiently while it was lying on its side, but not when it was upright.
Once I tightened it up, I checked for gaps with a thickness gauge, and there's still a .04 mm gap between some of the extrusions.
Does a gap this small matter?