XYZ calibration issues and what i did to solve them
First off all, i want to congratulate the Prusa team and give my compliments about the quality of the product in general, the quality of the kit assembly/user manuals.
It was a pleasure to build the kit and even more pleasure to see what this printer is capable of.
Great job guys !
I had some issues with a failing XYZ calibration : "XYZ calibration failed, please consult manual".
After some investigation i found a few problems that contributed to this issue. Maybe it helps others that have the same problem, apart from the standard things to check.
To make the Y-frame (thus heated bed) perpendicular to the X frame rods (that run parallel to the Z-frame), i had to adjust the M10 nuts that clamp the Z-frame to the Y-frame. I choose to adjust the nuts at the side of the power supply, because at the side of the RAMBO-box, the Z-frame should stay at about 10mm so the front left calibration point can be reached properly. But before adjusting the nuts at the side of the power supply, i did not loosen the 2 screws of the printed part that connects power supply box to the Y frame. While adjusting the M10 nuts, this printed part pulls at the Y-frame and will also pull at the Z-frame to which the power supply is bolted. So i guess it is best to loosen these 2 screws first before adjusting the M10 nuts, so you don't distort the Y-frame and/or Z-frame while adjusting the M10 nuts.
The Y frame belt idler and Y frame part that holds the stepper motor should be in line with the printed belt holder that is connected to the heated bed. When f.e. the stepper motor is not in line with the belt holder, the printer has trouble to move the heated bed up to the limit switch. I'm not sure if this can lead to a failed calibration, but all bits help in making it more stable.
The following image helped me a lot to get everything in line ; 
I found out that i did not snap the Y-frame 8mm smooth rods completely into the printed parts properly. I didn't realize that it needs quite some force to snap them in properly. The zip-ties held them in place, but snapping them in properly surely contributed to the stability of the frame.
The zip ties that hold the 3 bearings to the heated bed base plate have to be tightened with enough force so the heated bed is firmly connected to the Y-frame. I noticed that when the zip ties are tightened above the base plate, the ends of the zipties will touch the heated bed, so i tightened the zipties at the side of the bearings and with the ends pointing down. This also makes it easier to reach them when extra tightening is needed, because they have to be pulled real tight to clamp the bearings to the base plate properly and prevent extra play of the heated bed.
The PEANUT, euh PINDA probe needs to be adjusted so it is positioned about a millimeter lower than the extruder nozzle tip. I guess the nozzle tip position can vary between a series of extruders, so adjusting it using a picture of the probe position of another printer might not be precise enough.
After all these measures, the printer executes the XYZ-calibration flawless each time and prints like a charme.
Some questions i have :
1) Before starting a new XYZ calibration, is it usefull to do a RESET XYZ calibration first ?
Will a RESET XYZ calibration affect the calibration process in any way ?
2) The first step when executing the XYZ calibration is to move the Z-axes completely up against the end-stops. But i can imagine that, due to tolerances in the printed parts, it is possible that the Z-axis is not perpendicular (enough) with the heated bed plate. Can such tolerances lead to XYZ calibration errors, just because the endstops might not be a good reference ?
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Posted : 07/12/2016 1:01 pm
