Bands or jumps that repeat up the height of the part: lead screw, coupler and Z axis

Symptom

Bands, marked horizontal lines or small steps appear on the walls of the part and repeat along its height, sometimes every few millimetres; or the Z axis rises in jerks or makes noise when moving.

Likely causes, from most to least likely

1. A bent, dirty or unlubricated lead screw: the Z axis moves unevenly and some layers end up shifted or squashed (Anycubic). Bambu Lab greases the lead screws precisely to avoid jamming and layer lines.
2. A loose or misaligned coupler between the motor and the lead screw, or loose Z motor screws (Anycubic, Creality).
3. Loose grub screws on the lead screw or on the Z timing pulley, on printers with several lead screws linked by a belt (Creality).
4. Something is dragging the axis: debris on the lead screw, a damaged wheel, a deformed lead screw or a badly tilted bed (Creality).
5. It is not always mechanical: uneven extrusion, a fluctuating temperature or filament with an uneven diameter also leave bands (Anycubic, Bambu Lab).
6. A nozzle or hotend with play, or sudden layer height changes in the slicer: Bambu Lab names them as causes of irregular lines.

Checks to tell which one it is

• See whether the bands repeat at the same spacing or appear at random: Bambu Lab links irregular lines to a loose hotend, variable layer height or filament quality.
• Move the Z axis through its full travel and listen: it must go up and down smoothly, with no tight spots, knocks or squeaks.
• With the printer off, check the coupler and the Z motor screws: nothing should wobble.
• Check whether you use variable layer height in the slicer.

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 check the lead screw

   Switch off and unplug the printer. Clean the lead screw and check whether it is bent: Anycubic suggests removing it with an Allen key and rolling it on a flat surface; if there is a gap between the screw and the surface, it is bent and must be replaced.

   Check: The lead screw rolls without leaving a gap and is clean.

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

2. An aligned coupler and a firm motor

   Check that the coupler joins the motor shaft and the lead screw properly and is aligned with both before tightening its screws (Anycubic). Tighten the screws holding the Z motor and its bracket (Anycubic, Creality).

   Check: The lead screw turns without wobbling and the motor does not move.

   If that does not fix it: Check the Z grub screws and pulleys (next step).

3. Z grub screws and pulleys

   On printers with several lead screws linked by a belt, check the grub screws on the lead screw and its timing pulley and tighten them if loose; pull the Z belt by hand to see whether any pulley is noisy (Creality). If the lead screws have gone out of sync, follow your maker's guide before taking anything apart.

   Check: No pulley or lead screw has any play.

   If that does not fix it: Clean and lubricate (next step).

4. Clean and lubricate as your maker says

   Remove the dirt from the lead screw and the rods and lubricate them with what your printer's maker specifies. Careful: Prusa forbids lubricating the Z lead screws and nuts on the MK4/S and MK3.9/S, whereas Bambu Lab and Creality do grease them. Then move the axis up and down several times to spread the lubricant.

   Check: The Z axis moves up and down smoothly and quietly.

   If that does not fix it: Rule out extrusion and filament (next step).

5. Rule out extrusion and filament

   If the mechanics are fine, clean the nozzle, check that the hotend and nozzle have no play, measure the filament diameter or try another spool (Bambu Lab asks for 1.75 ± 0.02 mm) and, if you use variable layer height, enable its smooth mode (Bambu Lab). Anycubic also suggests keeping the room temperature stable.

   Check: The bands disappear or drop a lot.

   If that does not fix it: If they remain, contact the maker's support with photos of the part and a video of the Z axis moving.

Prevention

• Check and clean the Z axis at every maintenance, with your maker's lubricant and schedule.
• If you take the Z axis apart, align the coupler before tightening it.
• Keep the printer in a room with a stable temperature (Anycubic).

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:

• Fixing Z Banding/Wobble: How to Achieve Smooth and Consistent 3D Prints · Anycubic
• Z-Axis Abnormal Noise Handling Procedure (K1C) · Creality
• Troubleshooting for Ender-5 Max Z-axis Abnormal Noise · Creality
• Please lubricate the Z-axis lead screw (Z-axis maintenance) · Bambu Lab
• Troubleshooting and Solutions for 3D Printing Layer Lines · Bambu Lab
• Regular printer maintenance (MK4/S, MK3.9/S) · Prusa Research