UltiMaker 3 - Check the tension of the short belts

Maintaining correct tension on the short belts is important to ensure good print quality. The short belts transfer the movements of the X and Y motors to the print head. If the belts on the UltiMaker 3 are too loose, print head movement may not be accurate, which can cause print inaccuracies such as:

• Layer shifts: A sudden shift in the X or Y direction
• Leaning prints: Gradual shifting in the X or Y direction, making the print look like it's leaning.
• Incorrect angles: Acute or obtuse instead of straight angles, affecting the accuracy and how parts fit together.
• Ovals instead of circles: Similar to incorrect angles, a circle can come out as oval (too wide/narrow) in one direction.

Over time, the belts may become slack. Checking the belts is part of the UltiMaker 3 maintenance schedule. It is recommended to check the tension of the short belts at least once every three months or when you notice inaccuracies in your prints.

Checking instructions

Caution: Turn off the printer or ensure the UltiMaker 3 cannot accept new print jobs through the Digital Factory.

Pluck the two short belts to check their tension. They should resonate, like guitar strings. It should not be possible to press the belt against itself. Furthermore, the tension of the two belts should be equal.

Correct belt tension	Belt too loose

Tightening the short belts

To restore the tension, perform the following steps. Use the 2 mm hex screwdriver from the UltiMaker 3 accessory box.

1. Loosen the Y motor by using the hex screwdriver to loosen the four bolts that hold the Y motor to the left panel. Do not remove the bolts. The motor should be able to slide up and down.
2. Firmly press down on the motor with one hand. This ensures maximum tension on the short belt.
3. While still pressing the motor down, tighten the four bolts of the Y motor in a cross pattern. First tighten the top-left bolt, then the bottom-right, followed by the bottom-left and ending with the top-right. This ensures that the motor is attached straight.
4. Perform the above steps for the X motor that is attached to the back panel. Afterward, check the tension of both belts again.

Firmly push down on the motor	Tighten the motor bolts in the frame

Tip: After retightening the belts, especially when this was done because of print quality issues, run a quick test print to check right angles and circles. Look for a suitable print on Thingiverse.