Inaccurate calibration of Lulzbot Mini

General LulzBot Mini
1

Recently, the calibration process of my Mini becomes inaccurate. The nozzle is always a little bit lower than expected, and this can cause terrible results in the first 5 to 10 layers:

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As you can see, the skirt is abnormally wide, because the nozzle is squeezing the filament onto the printbed. Also, the nozzle is stirring in the printed part because it is ~1mm lower than expected. (This has nothing to do with the printing tape I added. Its thickness is negligible compared with the height error of the finished part.)
The situation could become better after it starts printing the internal supports with cavities, because the overflowed material has somewhere to go.
In the end, my printings end up with terrible surface finish on the bottom, and an unacceptably large error in height.
How can I solve this? The calibration process is automatic and I can do nothing with it. Where could things be wrong?

2

Check your Z-offset setting. The printer probes the washers and the offset is relative to the top of those washers. A washer is typically 1.5mm thick. But if you set that value the nozzle would be “on” the build plate. I find my printer needs a Z offset of roughly -1.1.

But never mind the number… look at the filament. You want a moderate amount of “squish” but not too much. If it doesn’t squish at all (nozzle too high) then the bottom of the filament barely has any surface area in contact with the the build plate … the part could break free of the build plate while you are printing.

You can also adjust your layer #1 filament flow. Normally 100% … but Cura will let you increase or decrease layer 1 … independent of the flow you use for all the other layers.

3

Thank you so much! My problem is solved.