Loose pulleys or grub screws: shifted layers, play and noises in the axes

Symptom

Layers shift like a staircase in X or Y, you feel play when moving the toolhead or the bed with the motor still, the belt runs crooked or an axis makes a strange noise, sometimes the Z axis when going up.

Likely causes, from most to least likely

1. A grub screw on the motor pulley has come loose or does not sit on the flat of the shaft: the pulley slips and the axis no longer follows the motor. Prusa names it as the main cause of staircase layer shifts.
2. A pulley misaligned with the one at the other end: the belt does not run straight and may rub (Prusa).
3. A loose motor or motor bracket: Prusa asks for the X and Y motors to be tight in their mount, and Creality checks the Z motor screws when it is noisy.
4. On the Z axis, loose grub screws on the lead screw or its timing pulley: Creality checks them when the Z axis is noisy going up.
5. Eccentric wheels with play or too tight, on printers with V-wheels (Elegoo).

Checks to tell which one it is

• With the printer off, hold the motor shaft by its flat with pliers and try to move the toolhead or bed: there must be no play (Prusa).
• Look at each pulley: both grub screws tight and one of them on the flat of the shaft (Prusa, Elegoo).
• Check that the belt runs straight between the two pulleys without rubbing.
• If your printer has V-wheels, gently push the carriage sideways: if it wobbles, check the eccentric wheels (Elegoo).

Before you start

Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.

Step-by-step fix

1. Switch off and find the loose pulley

   Switch off and unplug the printer. See which axis the part shifted in and check that motor's pulley. If you cannot see the grub screw, turn the motor by hand to bring it into view; on the MINI, Prusa suggests turning it from the move-axis menu; then switch the printer off again before tightening.

   Check: You can see both of the pulley's grub screws.

   If that does not fix it: If you cannot reach the pulley, follow your printer's disassembly guide.

2. Tighten the grub screws on the flat

   With an Allen key of exactly the right size (on the MINI, Prusa uses a 2 mm one), set one grub screw on the flat of the motor shaft and tighten both firmly (Prusa, Elegoo). If the pulley had moved, first line it up with the one at the other end so the belt runs straight.

   Check: With the motor shaft held, the toolhead or bed has no play any more.

   If that does not fix it: Check the motor and its bracket (next step).

3. A firm motor and bracket

   Tighten the screws holding the motor to its bracket (Prusa). On the Z axis, also check the motor screws (Creality, K1C) and the grub screws on the lead screw and its timing pulley (Creality, Ender-5 Max).

   Check: The motor does not move when you pull the belt.

   If that does not fix it: Adjust the eccentric wheels (next step).

4. Eccentric wheels with no play and no drag

   If your printer has V-wheels, turn the eccentric nuts with the supplied wrench until the carriage no longer wobbles but still moves smoothly, neither loose nor tight (Elegoo). Do it with the printer off and cold, as you sometimes need to remove the toolhead or the bed.

   Check: The carriage has no play and slides without jerks.

   If that does not fix it: Check the belt tension (next step).

5. Check the belt and test

   With everything tight, check the belt tension: Prusa wants it to sound like a low bass string when plucked, and Elegoo warns that an over-tight belt loads the motor. Then print a test part.

   Check: The part comes out without steps.

   If that does not fix it: If it shifts again, look for rubbing, lower speed and acceleration or check the motor with the layer shift guide.

Prevention

• At every maintenance, check that the pulley grub screws are still tight on the flat of the shaft (Prusa checks them every 200 hours on the MK4).
• Keep Allen keys in the sizes your printer uses at hand.

Still not fixed?

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Printers it applies to

Any FDM (filament) 3D printer, from any brand.

Official sources

This guide summarises the official documentation linked here:

• Layer shifting · Prusa Research
• Regular printer maintenance (MK4/S, MK3.9/S) · Prusa Research
• Layer Shift (FDM printer troubleshooting) · Elegoo
• Eccentric Wheel Adjustment (Neptune 4 / 4 Pro) · Elegoo
• Troubleshooting for Ender-5 Max Z-axis Abnormal Noise · Creality
• Z-Axis Abnormal Noise Handling Procedure (K1C) · Creality