How to Fix Z Banding and Layer Lines

Z banding is a pattern of horizontal ridges, repeating at fairly regular heights, on the side walls of a print. Sovol's troubleshooting guide describes it as lines that come from layers not lining up correctly as the print moves up the Z axis. It looks like brush streaks and is most visible on smooth, vertical, glossy surfaces.

The first job is to work out whether the lines are really Z banding. Several other defects look similar, and they have different fixes.

Is it really Z banding? Symptom table

1. Check the Z axis hardware

Mechanical causes are the classic source of regular banding. The Sovol guide lists a bent or misaligned lead screw, a dirty or dry screw, and loose couplers or bearings as the main ones. The steps it gives, simplified:

1. Switch the printer off and move the gantry by hand through the full height. It should move smoothly, with no tight spots or clicks.
2. Look at the coupler that joins each Z motor to its lead screw. Loose set screws let the screw wobble, which Sovol says can make the Z axis move unevenly.
3. If you can, remove the lead screw and roll it on a flat surface. If it does not roll straight, it is bent and the guide says to replace it.
4. On printers with two Z motors, measure from the base to the smooth rod on both sides. Both sides should match, and the guide says to adjust the motors until the rods are parallel.

Printers with a rigid, sealed Z system and no exposed lead screw often give you little to adjust. In that case, check the maker's maintenance guide and support channel before taking anything apart.

2. Clean and lubricate the lead screw

Old grease collects dust and can make the Z axis move in a rough way. Sovol suggests wiping the old lubricant off with isopropyl alcohol, applying a PTFE-based lubricant sparingly, and running the axis up and down to spread it. It suggests doing this about every three months. Use whatever lubricant your printer maker specifies, and avoid heavy grease, which attracts dirt. The maintenance routine on our 3D printer maintenance checklist page covers this with the rest of the upkeep.

3. Pick a layer height that suits the Z motor

The Z motor moves in discrete steps. A step is the lead screw pitch divided by the motor's full steps per revolution. For example, an 8 mm lead screw driven by a motor with 200 full steps per revolution moves 0.04 mm per full step (8 / 200). Layer heights that are multiples of that value, such as 0.08, 0.12, 0.16 and 0.20 mm, land on whole steps. Sovol's guide mentions a "magic number" layer height that matches the Z axis step size for the same reason.

This is printer-specific. Look up your printer's lead screw pitch and motor step angle in the maker's documentation before applying the arithmetic. Printers with belt-driven or differently geared Z axes work out differently.

Smaller layers can also make the bands harder to see. Sovol notes that many users find going from 0.2 mm to 0.1 mm makes them much less visible, at the cost of print time. See layer height explained for the trade-off.

4. Rule out model and cooling lines

Bambu Lab's wiki describes layer lines that appear only where the geometry changes, such as where the large bottom surface of a box meets thin walls, or on a boat hull. Its analysis points to shrinkage stress from bridging layers that touch the outer wall. The fixes it lists include:

• Add inner fillets or chamfers to the model so bridging does not contact the outer wall.
• Lower the fan speed for overhangs in the filament settings.
• Change the sparse infill pattern (for example gyroid or concentric) and reduce the infill to wall overlap.
• Print several parts at once to lengthen layer time.

Bambu's own note is that these changes help a great deal but may not fully remove the lines. Prusa describes a similar "hull line" on 3DBenchy that it traces to the sudden change from sparse infill to full top layers, and says this is not a hardware problem.

5. Check for random lines from the hotend and filament

If the lines are irregular, Bambu's guide points to three further causes:

• A loose hotend. The nozzle assembly should not wobble. On newer Bambu models this means checking the hotend clip and magnet; on X1 and P1 series it means checking the nozzle fastening screws.
• Abrupt variable layer height. If the lines match the places where layer height changes, use the smooth setting for variable layer height.
• Filament quality. Bambu recommends filament with consistent diameter (it quotes 1.75 mm plus or minus 0.02 mm) and suggests trying a different spool if you see uneven extrusion. Wet filament is another common reason, so try drying the spool.

Quick test to confirm the fix

Print a tall, smooth, single-wall cylinder or a vase-mode part, in a glossy filament, before and after each change. Light from the side makes bands easy to see. Change one thing at a time so you know which fix worked, and note the layer height so you can reuse it.

If the defect is really an X or Y problem, read how to fix ghosting and ringing. For a wider overview of print faults, see common 3D printer problems.