A regular repeating texture on the vertical surface of the print — evenly-spaced ridges or alternating thick/thin layers. The pattern repeats at a consistent interval matching the lead screw pitch (typically every 8mm on an M8 lead screw, or every 2mm on a T8 lead screw). This is different from ghosting, which is concentrated near corners.
Identify Z-Wobble vs. Inconsistent Extrusion
Z-wobble: The pattern repeats at a consistent, predictable interval that matches the lead screw pitch. The ridges appear on all four sides of a printed cube simultaneously. Getting worse doesn’t track with print speed changes.
Inconsistent extrusion: The pattern is irregular, changes with print speed, and appears more as varying line widths than regular ridges. This is an extruder or filament issue, not a Z-axis issue.
Print a tall cylinder and look at the pattern. Regular repeating ridges at consistent intervals = Z-wobble.
The Lead Screw Is Almost Always the Cause
Take the lead screw out and roll it on a flat glass surface. A bent screw will rock visibly. Even 0.3mm of runout across the screw length causes visible banding. Replace bent lead screws — they’re inexpensive and not worth trying to straighten.
A straight screw still causes wobble if it’s constrained at both ends. Z lead screws should be coupled to the motor at the bottom and left free at the top (no bearing at the top). A rigid top constraint forces the screw to transmit any eccentricity directly to the gantry.
Coupler Type Matters
Rigid couplers (solid aluminum hex couplers) transmit lead screw runout directly into the gantry motion. Flexible couplers (spider couplers, jaw couplers) absorb the small eccentricities in the screw and motor shaft alignment. If you have rigid couplers and Z-wobble, switch to flexible couplers. Don’t use jaw couplers on dual-Z setups — the compliance can allow one side to lag.
Linear Rails vs. Smooth Rods
Tight linear rails constrain the gantry well enough that a slightly eccentric lead screw can’t deflect it laterally. Smooth rods with LM8UU bearings allow more play, which means lead screw runout translates into visible surface variation. If you have smooth rods and persistent Z-wobble after replacing the lead screw, consider a rail upgrade or at minimum ensure the rods are parallel and the bearings aren’t worn.
Anti-Backlash Nuts
A brass nut on the lead screw with significant wear introduces backlash — the gantry moves freely for a fraction of a turn before the thread engages. This shows as inconsistent Z steps and a particular kind of banding that’s worse in one direction. Replace worn brass nuts with an anti-backlash nut (POM or Delrin). These are spring-loaded against the screw thread, eliminating backlash without excessive friction.
Lubrication
A dry or poorly-lubricated lead screw creates jerky Z movement that shows in the print surface. Wipe down the lead screw and apply a thin layer of PTFE-based grease (not oil — oil flings off onto the print). Re-lubricate every few months on actively-used printers.