Bed leveling and the first layer: the right Z-offset and what good looks like
Manual vs auto leveling, setting the Z-offset with paper and tuning it in 0.02-0.05 mm steps, telling a too-high, too-low and good first layer apart, and bed cleaning.
- Leveling the bed and setting the nozzle distance (Z-offset) are two different jobs. You need both, and auto leveling only does the first.
- A sheet of copy paper is about 0.1 mm thick and gives a safe starting point, but the final value comes from the printed line, not the number in the menu.
- A good first layer is lines pressed flat enough to touch with no ridges. Gaps between lines mean too high; ridges and curled edges mean too low.
- A dirty bed causes more first-layer failures than an unlevel one. Clean with 90%+ IPA, and occasionally with dish soap.
Almost every print that fails in its first ten minutes fails at the first layer. It is the foundation for everything above it; if it does not stick, or sticks only in places, the rest comes loose. This lesson covers two things people often treat as one, bed leveling and nozzle distance, and how to read what the first layer tells you.
The numbers assume an FDM printer with a 0.4 mm nozzle and a 0.2 mm first layer, the default in most profiles.
Two different jobs
Bed leveling makes the nozzle-to-bed distance the same everywhere: left equals right, front equals back. On a tilted bed one corner gets squashed while the opposite corner floats.
Z-offset (Prusa calls it Live Adjust Z) is the real distance from the nozzle tip to the bed surface when the printer believes it is at Z = 0. However level the bed is, if this value is wrong the whole first layer is wrong.
Auto leveling fixes the first job only. On almost every printer the second is still yours.
Manual: four screws and a sheet of paper
Many budget bed-slingers use four spring-loaded screws under the bed. The standard routine:
- Clean the bed and the nozzle tip of any stuck plastic. Heat the bed and nozzle to printing temperature first, because metal expands when hot. (Klipper’s docs choose to do it cold instead; the point is to do it at the same temperature every time.)
- Home, then move the nozzle over each corner screw.
- Slide one sheet of copy paper (about 0.1 mm thick) between nozzle and bed. Turn the screw until the paper moves but drags slightly.
- Go round all four corners at least twice, because each corner pulls on the opposite one, then check the centre.
Paper gives a safe start, not the answer, because every hand feels “slight drag” differently. The final value comes from the printed line.
Auto: what the sensor does for you
Most newer printers carry a bed sensor: inductive (PINDA and similar), a touch probe with a retracting pin (BLTouch and relatives), or a load cell that taps the bed with the nozzle itself. Before a print the machine probes a grid, say 3×3 or 4×4 points, and builds a height map (a mesh). During the first layers Z follows that map, so a slightly bowed bed still gets an even first layer.
What the mesh cannot do:
- It does not know the true nozzle distance. Most sensors sit beside the nozzle, not at its tip. The distance between where the sensor triggers and where the tip is, is the Z-offset you set yourself. (Load cells, which probe with the nozzle, are the exception.)
- It does not fix mechanics. A loose bed, a slack belt or a skewed axis stay broken; Klipper’s docs say plainly that software correction will not achieve perfect results. If the bed is badly tilted, bring it close with the screws and let the mesh handle the rest.
- Sensors drift with temperature. Many inductive probes trigger at a different height hot than cold. Klipper recommends probing at the same temperature every time, several minutes after reaching it.
Setting the Z-offset from a printed line
Print a single-layer test. Prusa printers have a First Layer Calibration menu that prints a zigzag then a solid square; on other machines use a 30×30 mm square one layer tall, several copies spread across the bed. Adjust the Z-offset from the menu while it prints and watch the line.
| What the line looks like | Meaning | Action |
|---|---|---|
| Round, rope-like lines; gaps between lines in the square; peels off easily | Nozzle too high | Lower the nozzle |
| Flat lines touching each other; smooth surface, no gaps, no ridges | Just right | Stop and save the value |
| Ridges between lines; square edges curl up; filament thin enough to see through | Nozzle too low | Raise the nozzle |
Prusa’s summary is that a good line is “flattened, but not squished.” On a textured sheet a too-high line looks round and a too-low line curls at the edges.
A tuning example. Start from the paper value and print the test square. There are faint gaps between every line across the whole sheet, so the nozzle is slightly high.
- Lower the nozzle by 0.05 mm and print again. The gaps are almost gone, but one corner still shows a faint groove.
- Lower another 0.02 mm. No gaps anywhere, no ridges, and the square peels off as one sheet. That is your value.
- If you overshoot and see ridges, back off 0.02 mm.
The steps are small because the first layer is only 0.2 mm tall; 0.1 mm is half a layer. Klipper describes the same work in “tens of microns” (0.01-0.05 mm).
The number in the menu means nothing across machines. Prusa says its own Live Z usually lands between -0.400 and -1.500 mm and must be judged by eye, not set to a figure; a touch-probe printer lives in a different range entirely. Redo it after changing the nozzle, the sheet or the hotend. Textured sheets are thinner than smooth ones and need their own value; printers with sheet profiles let you save one per sheet.
Cleaning the bed, the overlooked culprit
A first layer that looks right but still lets go is usually not a leveling problem but finger grease. From the Prusa Knowledge Base:
- Isopropyl alcohol (IPA), 90% or higher, before every print. Not rubbing or cosmetic alcohol, which contain oils and moisturisers.
- Warm water with a few drops of dish soap, occasionally, when IPA stops working; IPA does not remove sugars and some greases. Dry thoroughly; do not soak the sheet.
- Acetone only on smooth PEI, about once a month. Never on textured or satin sheets, and never before printing PETG.
- A PVA glue stick as a release layer for PETG, ABS/ASA, nylon, PC and flexibles. PETG on smooth PEI bonds so hard it can tear the coating; Prusa goes as far as saying not to print PETG on the smooth sheet at all.
- Do not touch the surface with bare fingers. Hold the sheet by its edges.
First-layer temperature and speed
Manufacturer figures; adjust for your filament.
| Material | Bed | Notes |
|---|---|---|
| PLA | 50-60 °C | If adhesion is still weak, go up about 5 °C |
| PETG | 80-90 °C | Fan off for the first few layers; textured sheet or glue stick |
| ABS | 100-120 °C | Use an enclosure; cold draughts lift the edges |
Simplify3D and Prusa both recommend a slower first layer, around 50-75% of normal speed, so each line has time to be pressed down and cool onto the bed. Prints that let go mid-way or warp are the subject of lesson 11.
Safety
The bed runs at 60-120 °C and the nozzle above 200 °C. Never check the gap with a finger while hot; use paper only. A nozzle pressed too low scrapes the sheet and blocks its own opening, which leads to a clog; if nothing comes out on the first layer, stop immediately. Do not leave the printer alone during the first layers.
Common mistakes
- Lowering the Z-offset to cure parts coming loose when the line already looks right. The fault is a dirty bed or temperature; over-squishing scars the sheet.
- Trusting a number from another machine or a video. It depends on that printer’s sensor, sheet and nozzle.
- Adjusting in 0.1 mm steps and jumping back and forth over the sweet spot.
- Leveling cold and printing hot, or switching between the two. Metal and sensors shift with temperature.
- A blob of plastic on the nozzle tip during the paper test, which throws the distance off by the blob’s thickness.
- Forgetting to clean after handling the sheet. One fingerprint is enough to lose that corner.
With the first layer sorted, the next step is understanding what each slicer setting trades for what.
Sources
FAQ
My printer has auto bed leveling. Do I still need to set the Z-offset?
Yes. The sensor measures where the bed tilts or bows and compensates, but the real distance from the nozzle tip to the bed still has to be set by you. The exception is printers with a load cell that probe with the nozzle itself.
How much should I change the Z-offset per step?
0.02-0.05 mm, then look at the result. The first layer is only 0.2 mm tall, so 0.1 mm is half a layer and changes the line dramatically.
The first layer will not stick. Should I lower the nozzle further?
Not to fix adhesion. If the line already looks right, the problem is usually a dirty bed, bed temperature or a first layer printed too fast. Going too low scars the sheet and can block the nozzle.
Circuits and code were tested on sample boards. Boards differ in pin layout, so check your board's pinout before you power anything.