XYZ Calibration compromised.
Front calibration points not reachable.
The solution of this error, the user manual says
Move the left / right Y threaded rods in the Z frame away from you
This is wrong. I had to pull the Z frame towards me so that the print bed gets closer to the probe.
Adjustment of Z frame’s position along the Y-axis is not practical. The easiest way I found is to flip the printer, top of the Z frame seats on the table. Slowly loosen left or right side M17 nuts backward or forward direction and tighten back enough to hold Z frame. Then do the same on other side. I used a vernier caliper to measure the distance between Z frame and the threaded rod crossing the two threaded rods to keep parallelism. If you loosen the bolts too much, the Y-axis frame will drop.
I suggest taking extra care of Y-axis frame when you assembly that prevents skewed XY plane later on. On page 44, 12.1 Nozzle/print surface gap is greater in the middle than at the corner describes how to check squareness of Y-axis frame.
Y-axis belt got loose during calibration. To prevent another incident, I secured the belt with zip ties.
If X, Y, and Z axis are in right angle, XZY calibration will report perpendicular.
Self test can’t tell faulty connection of the Hotend thermistor, which implies the user manually decide the thermistor’s condition.
I ran into bad connection of the Hotend thermistor during the troubleshooting of Mesh bed leveling failure. When I turned it on the printer, it shows MINTEMP ERROR. Then Hotend temperature was 19 degrees Celsius which was five to six degrees lower than room temperature.
Out of curiosity I ran Preheat. Hotend temperature was at 20 degrees Celsius when K-type thermometer of my multimeter indicated 110 degrees Celsius and kept rising.
I cut the 2-pin connector of the Hotend thermistor, installed new 2-pin connector. And the temperature reading of Hotend became fine.
Failure of Mesh bed leveling freezes the printer.
After successful XYZ calibration, whenever I tried to print a gcode file, Mesh bed leveling failed and freezed the printer. I spent a whole day to solve this problem. When it happened, previous calibration data wouldn’t be stored.
Calibration and bed leveling are complete different routine. I have experienced of Marlin, Repetier-Host, RepRapFirmwar-dc42. Calibration is part of the final stage of building a 3D Printer not a routine that the user chooses as a feature like auto bed leveling. Actually well-built machine does not require auto bed leveling before each printing.
I think this is grave bug that Prusa Rearch will have to fix ASAP.
The error message is:
Bed leveling failed. Sensor disconnected or cable broken. Waiting for reset.
On the user manual and Prusa Research’s support page the solution is:
Verify, whether the PINDA probe cable is plugged into the RAMBo board correctly. If it is the case, the PINDA probe is broken and it needs to be replaced.
I doubted it because XYZ calibration, Z calibration were successful many times. If it was bad connection of the probe cable, calibration would fail too. I thought it caused by firmware at some point. Later on out of frustration I remembered the suggestion of a user on Prusa Reasearch’s forum saying wrong probe’s height might trigger such error.
The fix was to lower the probe height 1.00 mm or 1.50 mm.
The first print
I ran V2calibration.gcode in the SD card three or four times to find the correct Z height, which was -0.800 mm.
The layer height was 0.15 mm. It took one hour forty minutes.