Z offset and first layer

The first layer makes or breaks a print. On the G1, the most common first-layer problem is a wrong Z offset — the distance between the nozzle tip and the bed at the start of printing.

Watch it

G1 Bed Level & Prep Surface — 4:49, official Ginger Additive video. More on Official videos.

Symptoms

• First layer is too squashed — very wide, glassy, hard to remove from the bed
• First layer is too high — round, “rope-like” lines that don’t stick, the print warps or detaches
• The nozzle drags or scratches the bed at the start of printing
• After a nozzle change, the first layer suddenly looks completely wrong
• After moving the machine or changing cables, the bed mesh “doesn’t load” correctly
• “It was fine yesterday, today the first layer is a mess”

Possible causes

1. Wrong live Z offset — most common; just needs adjustment
2. Nozzle changed but Z offset not updated — different nozzle = different protrusion → different Z
3. Bed mesh leveling not saved correctly — saved from display but G-code expects the slicer’s mesh
4. Probe Z offset drifted — the bed-leveling probe and the nozzle have different Z offsets, which can drift after cable / endstop changes
5. Bed not flat / not clean — debris, residue, scratches under the nozzle

How to know the Z offset is right

There is one test, and it is a measurement rather than an opinion:

Measure the layer, compare it with the slicer

Print a first layer, then measure its height with a caliper. It must equal the layer height set in the slicer. If it does not, the Z offset is wrong — and the difference tells you which way to move it.

This works on the G1 because the layers are millimetres thick. Filament printers rely on how the first layer looks because nobody can measure 0.2 mm reliably; here you can simply measure it, so there is no reason to judge by eye.

The visual signs below are useful for spotting a problem quickly mid-print, but the caliper is what settles it.

Adjusting live during the first layer

1. Start the print
2. Watch the first lines (skirt or first wall)
3. While printing, on the printer display open the Tune / Z offset menu
4. Adjust in small steps (0.05 mm)

What you see	Action
Lines too squashed, very wide, shiny	Raise Z offset (positive direction, +0.05 mm)
Lines round, rope-like, lifting	Lower Z offset (negative direction, −0.05 mm)
Nozzle scratching the bed	Stop the print immediately, raise Z offset by +0.1 mm before restarting

Typical adjustments are within ±0.7 mm of the saved baseline. Once you find the right value, save it from the display so it persists.

After a nozzle change

Different nozzles have different lengths. The Z offset is invalidated every time you swap nozzles.

1. Re-run bed leveling with the new nozzle installed
2. Re-tune the live Z offset on the first print
3. Save the new Z offset

If the mesh runs but the height is still wrong

The pattern: levelling visibly probes the bed, the heightmap looks sensible, and then the nozzle starts the print far too high or too low.

This is worth understanding, because the printer has two different ways of getting a mesh and the slicer decides which one is used.

Mode	What the printer does
Adaptive (KAMP_LEVELING=1 from the slicer)	Probes the bed fresh at the start of every print, over the area the part actually occupies. Whatever you saved earlier is ignored
Stored (anything else)	Loads the mesh saved under the name global. Nothing is probed

So in stored mode there has to be a mesh called global, and only one thing creates it: the BED_LEVEL macro, which probes and saves under that name.

A mesh made any other way is not the one the printer loads

Running BED_MESH_CALIBRATE from the console and then SAVE_CONFIG stores the result as default, not global. It looks saved, the heightmap shows it, and the printer will not use it.

Use the BED_LEVEL macro button. That is what puts the mesh where the print sequence looks for it.

Fix

1. Run BED_LEVEL from the macro buttons — not BED_MESH_CALIBRATE from the console
2. Let it finish; it saves the profile itself
3. Reprint

If the probe and nozzle have different Z offsets

After replacing endstops, cables, or moving the machine, the probe Z offset can drift relative to the nozzle. Symptom: bed mesh looks right but the nozzle hits the bed (or stays way too high) at print start.

1. From the printer display, find the Z offset tuning menu
2. Run a print and adjust live Z offset to the correct value
3. Save the new probe-vs-nozzle Z offset

Diagnostic flow

First layer wrong
        │
        ├── Wrong everywhere uniformly?
        │       └── Live Z offset adjustment
        │
        ├── Wrong only after nozzle change?
        │       └── Re-level, re-tune Z offset, save
        │
        ├── Mesh ran but Z is way off?
        │       └── Re-run it with the BED_LEVEL macro
        │           (not BED_MESH_CALIBRATE)
        │
        └── Wrong only in some regions?
                └── Bed not flat / debris / surface damaged
                    Clean the bed, re-level

How to prevent

• Always re-level after a nozzle change before printing
• After moving the machine, run a fresh bed leveling
• Keep the bed surface clean — wipe with isopropyl alcohol between materials
• Don’t change endstops or homing-related cables without re-running calibration
• Save your final Z offset to firmware via the display

Notes

• The single most common first-print problem after the assembly is finished
• Live Z offset tuning is quick, and worth learning once — it is the adjustment you will reach for most often
• Saving from the display vs. saving from the computer: small but real source of confusion

Related notes

• Bed leveling system
• Rotation Volume calibration
• Nozzle set
• Bed adhesion sprays