Z Banding (Z Wobble): Regular Lines on the Side of a Print

If the side of the part has horizontal lines repeating at equal intervals, as if drawn with a ruler, the problem is most likely in the Z axis. A bent screw, a misaligned coupler, motor steps that do not match the layer height or a fluctuating bed temperature can create these regular bands. Measuring the distance between the bands is the shortest way to find out which it is.

Symptoms

• Lines repeating at equal intervals along the full height of the part's side.
• Layers shifting left and right at regular intervals, a wavy surface.
• The distance between bands is usually constant, for example every 2 mm or 8 mm.

Lines at irregular intervals or only in certain sections have different causes, such as under-extrusion or temperature fluctuation.

Measure the band spacing

The distance between bands is the key to finding the cause.

• Measure the total distance across 10 bands with calipers and divide by 10.
• If this distance equals the pitch (lead) of the Z screw (2 mm or 8 mm on many printers), the problem is most likely in the Z screw or the coupler.
• If the bands are irregular, or the spacing does not match the screw pitch, look at temperature and extrusion fluctuations.

1. Check the Z screw and coupler

• Bent screw: If the Z screw is not straight, it pushes the toolhead or the bed slightly sideways on every turn. Rotate the screw without taking it out of the printer and see whether its top end wobbles.
• Coupler alignment: The coupler that joins the motor shaft to the screw produces wobble if the motor and screw are not perfectly aligned. Loosen the coupler screws, run the Z axis to the very bottom and top, then tighten again.
• Lead screw nut: If the brass nut is fixed too rigidly to the body, it passes the screw's bend on to the carriage. Loosen the nut's screws slightly, move the axis up and down, then tighten again. Some people use mounts that let the nut float slightly.
• Top end of the screw: If there is a retaining bearing at the top of the screw, it may be straining the screw. If the screw is bent, the top bearing increases the wobble.

2. Clean and lubricate the Z axis

• Clean the screw and apply a thin coat of the lubricant or grease the manufacturer recommends.
• Make sure the Z axis moves up and down freely by hand (with the motors off).
• On printers with two Z motors, check that both sides are at the same height. If one side is higher, the carriage moves crooked.

3. Tighten loose parts

If the wheels or bearings on the X axis carriage have play, the head shifts slightly with every layer change. Adjust the eccentric nuts on the wheels and check the rails and screws.

4. Choose a layer height that matches the motor step

Stepper motors are most stable at their "full step" positions. If your layer height is not a multiple of these steps, some layers come out a few microns thick and some thin, and that creates regular bands.

• For a 1.8° motor and an 8 mm lead screw, the full step is 8 / 200 = 0.04 mm.
• In that case choose layer heights that are multiples of 0.04, such as 0.12, 0.16, 0.20, 0.24 and 0.28 mm.
• With a 2 mm lead screw the full step is 0.01 mm and almost any layer height is compatible.

Detailed explanation: Choosing layer height.

5. Check bed temperature fluctuation

On some printers the bed heater works in "on-off" (bang-bang) mode. The bed expands as it heats and shrinks as it cools, and this moves the bed up and down at the micron level on every cycle. That creates regular bands on the surface.

• Watch the bed temperature on the screen. If it swings more than ±1 °C, do a PID tune for the bed too.
• If bed PID is off in the firmware, you may need to turn it on.

6. Extrusion and temperature fluctuations

• Check that the nozzle temperature stays steady.
• If the filament diameter is inconsistent, the amount of extrusion varies and irregular bands appear.
• Air drafts near the printer also create layer-to-layer differences.

When is it normal?

No FDM print has a completely flawless side surface. Very faint bands that only show in light from a certain angle are normal. Bands you can feel with a finger and see clearly can be reduced a great deal with the checks above.

How do I tell Z banding from ghosting?

Z banding shows as horizontal bands along the height of the part and repeats across the whole surface. Ghosting is waves that fade out horizontally after corners.

Can I fix a bent Z screw?

Slight bends can be tolerated by mounting the lead screw nut loosely. For a clear bend the best fix is to replace the screw; screws are cheap and widely available parts.