Regular Ridges Around the Walls (Z Banding and Z Wobble)

Likely causes, most common first

1. Play in the hotend, carriage or bedMost common
   Polymaker calls a loose extruder carriage and hotend probably the most common cause, followed by worn bearings, loose rollers and a bed with free play. Screws loosen over time with constant movement.
2. Loose beltsCommon
   Polymaker lists a loose belt as the next most common reason after loose parts, and says X and Y belts should have no droop.
3. Z lead screw problemsCommon
   A bent or wobbling Z rod, a lead screw that does not run straight into its coupler, or backlash in the Z nut. On printers with several belt-linked Z screws, Bambu Lab describes a loose timing pulley or a slipped Z belt putting the Z sliders out of sync.
4. Z hop on a printer with a weak or misaligned Z axisOccasional
   Polymaker found that removing Z hop made layer bulges disappear on older single lead screw printers: the axis may lift slightly less than it lowers, squashing a layer.
5. Dry or binding rods and a stiff bedOccasional
   Polymaker suggests lubricating guide rods and lead screws on rod-based machines and checking that the bed moves freely, since over-tightened bed corners add friction.
6. Tall, thin part on a moving bedOccasional
   On bed-moving printers the part itself can sway as the bed moves, so the top shows wobble while the bottom looks fine.
7. Extrusion or temperature changing during the printLess common
   Temporary under-extrusion, a fan cooling the heater block, or speed changes on small layers can leave bands that mechanics do not explain. See Under-Extrusion.

Fix it, one change at a time

1. Tighten the hotend and carriage. With the printer off and cold, check the screws holding the hotend and extruder to the carriage. Replace worn printed parts. If the nozzle or heater block itself is loose, follow your printer maker's procedure for tightening it, since most require doing it hot with the right tools; do not improvise.
2. Remove play from the bearings, rollers and bed. Adjust rollers on V-slot frames so they do not spin freely, replace worn bearings, and tighten the bed mounting screws.
3. Set belt tension by the printer maker's method so there is no droop. Polymaker warns that too tight causes other problems, so avoid overdoing it.
4. Inspect the Z axis. Look for a lead screw that wobbles as Z moves, one that does not drop straight into its coupler, or a loose coupler or timing pulley. Replace a bent rod. On printers with belt-linked Z screws, follow the maker's procedure (Bambu Lab publishes one for re-locking the Z pulley and resyncing the sliders).
5. Lubricate as the maker says. Clean and lubricate rods and lead screws with the lubricant your printer maker specifies, then move each axis by hand to spread it.
6. Test without Z hop on older single lead screw printers. If the bands go, keep it off and use the slicer's avoid-crossing-walls travel option instead to stop the nozzle dragging.
7. For tall, thin parts, add a small sacrificial support next to the part, print it lying down, or split it. A brim helps adhesion but will not stop a tall, skinny part from wobbling.
8. If the mechanics are sound, look for extrusion and temperature causes: check that the fan does not blow on the heater block, use the slicer's layer view to see whether speed changes at the banded heights, and calibrate flow.

Confirm it is fixed

Print a plain cylinder or box with one or two walls, at least a few centimeters tall, with the same filament. Look along the wall under a raking light. The surface should be even, with no regular ridges wrapping around it. If the bands only got lighter, repeat the rattle test: one loose part often hides another.

Why it happens

Each layer is printed at a slightly different place if anything in the machine can move when it should not. A hotend that rocks a fraction of a millimeter, a bed with play in its rollers, or a lead screw that pushes the gantry slightly sideways on every turn all shift the layer a little, and the next layer shifts back. Repeated up the wall, those shifts read as ridges. Polymaker stresses that this is a frame and hardware problem: perfect slicer settings will not fix it.

The Z axis adds its own version. Polymaker traces layer bulges on older single lead screw printers to a lead screw that is not quite at 90 degrees to the bed, and notes the axis may lift less than it lowers, which is why Z hop can make the bands worse on those machines. Bands that appear only at certain heights are often something else entirely, such as temporary under-extrusion, which is why the slicer's layer view is worth checking before any hardware work.

Z banding and ghosting are easy to confuse but come from different motion. Ringing is X and Y vibration after a sharp change of direction, so it appears just after corners and fades. Banding runs all the way around the part. If layers jump sideways by a large amount rather than wobbling, read Layer Shifting.