MK3 Kit - XYZ Calibration problems
Here is the way the story goes...
Assembled the printer. Self-test hung up on the X test. Fixed that by updating the BIOS and moving a rogue ziptie back into position. Self-test passed.
XYZ Calibration started. Z goes up. Z comes down. Auto-fail. Check the axes. Moved the PINDA (several times). Same result. Checked the forums. Realized that extruder was in too low. Disassembled and reassembled correctly. Prayed. Same result. Updated the BIOS again. Same result. Moved the PINDA. Same result.
I’m starting to feel a little disheartened now. I’ve tried everything on the forums I could find to no avail. It still keeps saying to ‘Check the axes’. I’ve got no idea what to do anymore. Hopefully someone on here can help me figure out what’s wrong. There is only one weird thing that is does during calibration that I noticed. When the Z is going all the way up to the top, the right motor keeps going for a second after the left motor hits the top (enough to make the x-axis bars crooked). Then it asks if the plate is on the base and to clean the extruder before it descends and fails. Not sure if that means anything, but I want to give you guys the full picture.
Thanks for any help you can give. 
Thanks,
Greg Remind me to put something witty or profound here sometime in the future.
Re: MK3 Kit - XYZ Calibration problems
It’s something with the left z-axis motor - it seems to get caught on sonething that I can’t see and won’t go up all the way. I’m sure of this because I manually moved the left side up all the way and it passed the xyz calibration.
Thanks,
Greg Remind me to put something witty or profound here sometime in the future.
Re: MK3 Kit - XYZ Calibration problems
Make sure your Z-screw cover on the left is not screwed down too tight http://manual.prusa3d.com/Guide/4.+Z-axis+assembly/509?lang=en 
Also loosen the four motor screws on the left and the top bracket screws. Run your X carriage to the top and bottom a couple of times then take it back right to the top. While it is there carefully tighten the left top bracket bracket screws one at a time, a little at a time. Then take the axis right to the bottom and retighten the motor screws again one at a time in the usual diagonal pattern. This will ensure that the left side assembly is as aligned as possible with the frame and components.
Let us know how you get on.
Re: MK3 Kit - XYZ Calibration problems
I too am having issues with the MK3 kit and the XYZ calibration. Here is what I have seen on my new kit, which I received 4/2 and assembled by 4/6.
I finished assembly by Friday evening, and was really excited that I was almost ready to print! I went through the pre-flight check and all looked good. Then I started the unit up and went through self test. The self test completed without any issues and it moved on to the XYZ calibration.
First step is to find the 4 calibration points. Point 1 proceeds, and about 2 minutes later it does a little dance once it has found the spot, it goes up and down in small movements 3 times then fines tunes location. It then proceeds t point 2 and does the same. Point 3 it starts the same way, it seems like it finds the point, but it does not do the little 3 step up/down movement and then fine tune, it just heads right to the point 4. and at Point four, it does the same as point3. Then it pauses and starts iteration 2, and repeats the entire process. Then iteration 3 and repeats the entire process again. At the end of iteration 3 it says it failed and consult manual.
The bed has been checked for square between bed and x-axis rods as well as between bed and z-axis main metal frame. I checked the bed with a speed square to the frame and a flat ruler between the bed and frame to check if parallel. I have pics of all this as well and a video of the little 3 step movement.
I flashed the firmware and tried again, no luck.
I flashed the firmware with the previous version, in case it was 3.1.3 problem, and still failed.
The unit auto homes OK.
I checked the bed to hot end at all 4 corners without moving the z axis, and the distance is within a sheet of paper at all corners.
I am thinking there is a heat bed issue, sensor issue or software issue. Chatting with someone from Prusa and they guessed maybe sensor or heat bed, waiting for them to confirm by Monday.
Has this happened to anyone else? Did anyone have a sensor or heat bed issue?
Re: MK3 Kit - XYZ Calibration problems
Hello,
I´m having the same issue and drive crazy to me.
I´m thinking to disassembly again but tring to found a solution iun the forum before.
Thanks to help me with more feedback on this topic to get more ideas.
I´m thinking that for some reason this issue happen so often on this model.
Please if you get the answer or solution thanks to let me know.
BR
Re: MK3 Kit - XYZ Calibration problems
I found my issue.
I had run through the self test and all seemed OK, the printer said OK for X, Y, Z, hot end, bed and filament sensor.
Then when it tried to do the xyz calibration it did three iterations of finding 4 points and failed, never improved.
The problem I had was the x-axis pulley on the motor. Apparently the pulley was on the shaft and the two set screws were tight enough to pass the self test of x-axis but they were not completely tight. I could slightly rotate the pulley screws, and when I checked the screws, both of them could be tightened. Once the screws were completely tight and there was no play in the pulley, the unit did the complete calibration.
My calibration came back with a skew of 0.00 and the y axis to origin was 10.38 and 10.30 ( or something similar, doing from memory.)
Re: MK3 Kit - XYZ Calibration problems
I had a similar behavior; turned out all I had to do was swing the filament bracket around to the back. If it's in front, the Y carriage taps it on the way up and caused an error.
Re: MK3 Kit - XYZ Calibration problems
I experienced that problem when I first received the MK3. In my case I found that the 3d printed part a the top of the z axis was screwed down to a point where it cause friction between the z-axis and the plastic, which therefore caused the machine to think it was at the top of the axis. Try loosening the two screws holding it to the frame until it is little bit loose. If that doesn't work I would try getting lithium grease to try and make the z travel smooth.