Layer shifting — the print offset sideways, 6 causes

Symptom: at a certain height the whole print jumps sideways. Everything below is fine, everything above is offset by a few millimetres on the X or Y axis and carries on printing parallel to the lower part. Sometimes the shift happens once, sometimes it repeats several times and the model looks like a flight of steps.

Layer shifting means the stepper motor has lost steps. The controller sent the pulses, the axis did not execute them, and the printer has no idea, because a typical FDM machine has no feedback from the axes. From that moment the whole coordinate system is offset and the error stays in the print for good. The cause is always mechanical or electrical, never in the material. Filament can at most make things worse indirectly, if a warped print starts to foul the nozzle.

Most common causes and fixes

1. The toothed belt is too loose or worn through

A loose belt lets the pulley skip a tooth on a sharp change of direction. The preliminary symptom, before a full skip, is ghosting on the walls and round holes that come out slightly oval.

How to check: with the motors off, pluck the belt with a finger at the midpoint of its length. It should answer with a short, clear note rather than waving softly. Judge the slack on both sides of the axis, because often one pulley is tensioned and the other is not. While you are there, look at the teeth against the light: worn, rounded teeth or a fraying cord mean the end of the belt's life.

What to do: tension the belt with the tensioner screw or by moving the motor. The aim is a firm tension but not an extreme one, because an over-tightened belt removes backlash at the cost of the motor bearings and stretches itself. After tensioning, move the axis through its full travel by hand and check that there is nowhere the resistance increases.

2. The pulley grub screw has worked loose

This is the most insidious cause, because the printer looks healthy. The pulley seated on the motor shaft is held by one or two grub screws. When such a screw loosens, the pulley turns with the shaft most of the time and only slips under greater acceleration.

How to check: grip the pulley with your fingers and try to turn it relative to the shaft. Any perceptible play is a verdict. The characteristic symptom is a shift that happens irregularly and always on the same axis.

What to do: tighten the screw so that it lands on the flat of the shaft, not on the round part. If the pulley has two screws, the first always goes on the flat. A drop of medium-strength threadlocker lets you forget about the problem for a long time.

3. The motor current is too low or the driver is overheating

A stepper motor with the current set too low does not have the torque needed to stop the moving mass of the hotend. A separate variant of the same problem is a driver that reaches its protection temperature on a longer print and briefly limits its output. The shifts then only appear after an hour or two, and the first layers are faultless.

How to check: touch the driver heatsink immediately after a failed print and compare it with the others. Check as well whether the motor is hot to a degree at which you cannot keep your hand on it. Repeatability over time is the best clue here: a temperature-dependent failure always shows up later than a mechanical one.

What to do: raise the motor current by a small step in line with the documentation for your board, and then see to the cooling of the electronics. A case fan directed at the drivers solves this problem more cheaply than replacing anything. If the printer has an enclosed chamber for ABS or ASA, make sure the electronics are outside the 50 °C zone.

4. Speed and acceleration exceed what the mechanics can do

Profiles imported from the internet are sometimes written for printers with a completely different moving mass. An acceleration that a CoreXY with a light hotend will perform without blinking leads, on a machine with a moving bed, to lost steps on the Y axis, because there it is the bed together with the print that is the mass to be stopped. The taller the print, the worse, and that is why shifts usually appear in the upper part of the model.

What to do: lower both print speed and acceleration by about a third, then work back up in small steps. Pay particular attention to travel speed, because that is usually the fastest move in the whole print and it is the one that loses steps. If your printer has a jerk or junction deviation parameter, lower that second.

5. The nozzle catches on a warped or lifted print

A corner that has risen above the printing plane becomes an obstacle. The hotend strikes it during a travel move, the axis loses steps and the print jumps. This is the only cause on this list where the material matters: the shrinkage of ABS, ABS/CF, PC/ABS and ASA is high, so those polymers warp most readily and most often lead to a collision.

How to check: listen to the print. A knock every time the hotend passes over the same place is a warning sign that usually precedes the shift by a quarter of an hour or so.

What to do: tackle the cause, that is warping. High-shrinkage materials require an enclosed chamber and a hot bed, and the appropriate ranges are given in the table below. As an immediate measure enable Z hop in the slicer so the hotend lifts on travel moves, but treat that as a crutch rather than a solution.

Porima material	Bed	Chamber	Tendency to warp
PLA	0–60 °C	open	low
PETG	60–80 °C	open	low
HT PETG	100–120 °C	enclosed recommended, adhesive advised	moderate
ABS	80–110 °C	enclosed, 50 °C	high
ABS/CF	80–110 °C	enclosed, 50 °C	high
ASA	90–120 °C	enclosed, 50 °C	moderate
PC/ABS	100–120 °C	enclosed, 50 °C	high
PA (nylon)	90–120 °C	enclosed and heated	moderate

Source: the official FDM technical data table from the manufacturer, Porima. Full set of ranges: print temperature table.

6. Something is obstructing the movement of an axis

Dirty or dried-out rails, a cable pulled into the path of movement, a cable tie rubbing against the frame, a filament holder standing too close, a deformed roller on an extrusion. Each of these increases resistance over part of the travel and causes steps to be lost always at roughly the same place.

How to check: switch the motors off and move the hotend slowly by hand through the full range of the axis, then do the same with the bed. The resistance should be the same from end to end. Every place where it drags needs inspection.

What to do: clean the rails and apply a thin layer of grease intended for linear rolling elements. Do not lubricate the belts or the pulleys. Tidy up the cable looms, and adjust the rollers on the extrusions with the eccentric so that they can be turned with a finger against slight resistance rather than spinning freely.

How to tell a shift from other defects

It is worth taking a moment on identification, because three different faults look similar. A layer shift is a one-off and sharp: there is a single layer above which everything is offset by the same amount. Ghosting repeats over the whole height as a faint echo after every edge and does not displace the geometry. Play in the Z axis, in turn, gives regular bands every few millimetres which return to the original line instead of staying offset.

If the shift always occurs at the same height on the same model, the cause is almost certainly in the file or in a collision with the print. If it happens somewhere different every time, look for play, motor current or driver temperature.

Related problems

• Ghosting — a loose belt first gives an echo on the walls, and only then loses steps.
• Warping — a lifted corner of the print is the most common physical obstacle for the hotend.
• Dimensional accuracy and shrinkage — oval holes and wrong dimensions foreshadow play in the mechanics.
• The printer stops extruding mid-print — can also result from an overheated driver.
• Blobs & zits — a collision between the nozzle and a lump on the wall is sometimes the start of a shift.
• The print will not come off the bed — the other side of the same balance between adhesion and stress.