Quick diagnosis
Skipping layers means the Z axis fails to rise the full expected height for one or more layers, so new material either gets crushed into the layer below it or a chunk of the part’s total height goes missing. This is different from a layer shift, which is a sideways X or Y offset, and different from z-banding, where the axis keeps moving but unevenly, producing a repeating ripple rather than a missing or compressed section.
1. Confirm the axis, not just the symptom
Measure the height of the affected section against what the model and layer count expect. A section that is genuinely shorter than it should be, or where several layers look fused into the thickness of one, points to a real Z-height problem. If the print instead shows a sideways offset or a repeating ripple that does not change the total height, work through the layer-shift or z-banding guides instead.
2. Check for mechanical binding
Power off, let the printer cool, and move the gantry up and down by hand with the Z motor disconnected, the same check used for z-banding. Binding at any point in the travel, not just a wobble, points to a dry or dirty leadscrew, debris on a rod, or a gantry that is not parallel to the rails. A stepper motor that cannot overcome resistance will simply fail to move for that step rather than moving unevenly, which is what separates a skipped layer from a banding ripple.
3. Check the coupler and driver for slipping steps entirely
A grub screw seated on the round part of the motor shaft rather than its flat can let the shaft spin freely under load instead of turning the leadscrew at all for that moment, which drops a full step rather than just introducing play. A Z driver running hot enough to thermal-throttle under sustained load can have a similar effect, especially on tall prints where the axis rarely gets a break. Check that grub screws are tight on the shaft flats and that the driver and stepper are not running unusually hot for the printer.
4. Match layer height to the axis’s real resolution
Every Z axis has a physical step resolution set by its motor, leadscrew pitch and microstepping configuration, and a layer height that does not divide cleanly into that resolution forces the firmware to round on some layers and not others. Stick to layer heights the printer manufacturer documents as tested values rather than an arbitrary fraction, particularly on printers with an unusual leadscrew pitch or a non-default microstepping setting.
5. Rule out a gcode or recovery-level cause
A print resumed after a power loss or a paused/thermal-runaway recovery does not always restore the exact Z position it left off at, and a corrupted or truncated gcode file can occasionally omit a movement command outright. Treat any print that survived a power interruption or a firmware-triggered pause as a candidate for a Z discrepancy at that exact point, and verify height at the resumed layer before trusting the rest of the job. If skipped layers only ever appear after this kind of interruption, the fix is in how the recovery is handled, not in the mechanical Z axis itself.
Skipping layers checklist
- Confirmed missing/compressed height, not a sideways shift or a repeating ripple.
- Gantry moves freely by hand with the Z motor disconnected.
- Coupler grub screws are tight on the shaft flats; driver is not overheating.
- Layer height matches a manufacturer-tested value for the axis’s resolution.
- Any power-loss or pause/recovery event has been checked against the affected height.