Occasionally, you might see a sudden shift on your print. It could look something like this:
This is a different issue from the slanting or leaning print issue explained here.
What is a hard shift?
The short answer: A hard shift occurs when the X or Y motor misses a step (or several).
The long answer: Your Ultimaker printer learns its origin point at that the start of every print by finding the home position with the endstops, and counting steps after leaving the home position. If your motor encounters resistance during printing, it won't move the right number of steps. However, the printer doesn't have any way to know that it didn't move the right number of steps. This will cause your print to continue building, but at a shifted position from where it should be.
Why does this happen?
The short answer: Your printhead encountered resistance while trying to move.
The long answer: Your printhead encountered resistance while trying to move; sometimes these things happen. If it happens once, it's not a critical issue, but there are some maintenance items you should check before resuming printing. If it happens repeatedly, and the maintenance issues have already been checked, there are other things to check.
Maintenance issues (check if this happens once):
- Are the printhead shafts and perimeter rods on the XY gantry clean?
- Are the printhead shafts and perimeter rods on the XY gantry well-lubricated?
- Are your sliding blocks and pulleys in proper alignment?
- How does the printhead feel when you move it by hand? Are there unusual noises from the bearings?
- Are your short belts adequately tight?
Other issues (if maintenance issues have already been ruled out and you experience shifts again):
- Are you enclosing your printer? To confirm that nothing is overheating, try removing the enclosure and printing.
- If you feel resistance from one motor in particular and you've already checked the belt tension, unscrew the motor and turn the motor by hand. Check how difficult it is to move. It should turn pretty easily; I recommend leaving the motor pulley in place while you do this as it's easier to grip than the shaft itself.
- If the shift always happens on the same axis, you can try switching the X and Y motors to confirm whether the issue is with the motor itself, or the electronics board.