Inconsistent first layer calibration (solved)
I have been the proud owner of a Mk4 for some time now. I upgraded it myself from the Mk3, which I also received as a kit at the time.
So far so good. I enjoyed the new features, including the automatic first layer calibration using a load cell.
One day I realized that, contrary to my expectations, the first layer was not perfect everywhere. Quite the opposite. Somewhere on the print bed, the first layer was suddenly calibrated far too high, which meant that the object barely made contact with the print bed at this point. At first I dismissed this as a one-off.
Unfortunately, from then on it happened again and again that the calibration of the first layer did not work everywhere. Sometimes the layer was too high at one point of the print bed, sometimes too low. Incorrect measurements happened randomly all over the print bed.
It got to the point where the nozzle ground on the print bed after an incorrect calibration point.
I then worked through all the possible causes according to the forum/internet.
- Clean the nozzle to avoid incorrect measurements of the load cell due to filament residues.- Clean the print bed incl. sheets from all sides to prevent dust and other particles from falsifying measurements- Loosen the filament spool slightly so that there is no tension on the print head during the measurements- tighten the nozzle and make sure that it sits firmly in the print head. - Tighten all screws on the print bed in the specified order.
None of this had any effect.
A footnote in one of the forum posts finally led me to the solution:
Trapezoidal nuts of the Z-axis
It turned out that the trapezoid nuts had a lot of play and no longer sat snugly on the threaded rods of the Z-axis motors.
This made it possible to move the entire Z-axis up and down in the micrometer range.
This in turn distorted the measurements of the weighing cell at different locations on the printing bed in different ways, depending on the position of the thread.
After replacing both nuts, the Z-axis can no longer be moved and the calibration of the first layer immediately works reliably again across the entire print bed.
I hope I can help others with this experience report who have the same or similar problems with the Mk4 and the calibration of the first layer.
Translated with www.DeepL.com/Translator (free version)