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.