There is no single setting that smooths every surface. The change depends on which face is rough. For a flat, visible top, enable ironing in your slicer. For visible layer steps on a sloped or curved wall, lower the layer height, or use adaptive layer height if your slicer supports it. For a rough bottom face, the fix is in the first layer and the bed, not in ironing.
The sections below help you identify the defect first, then choose the setting that targets it. No universal numeric profile exists for this, because printer, slicer, nozzle, filament, and the defect all change the answer.
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Identify which surface is rough
“Smooth finish” covers several different problems. Each one has a different cause and a different first setting, so match the symptom before you touch any values.
| Visible defect | Where it shows up | What it means | Setting to change first |
|---|---|---|---|
| Gaps, grooves, or raised ridges on a top face | Lids, badges, nameplates, flat tops | Top infill lines leave holes or bumps between them | Ironing |
| Stepped lines on a sloped or curved wall | Angled sides, chamfers, domes | Each layer leaves a visible step on a slope | Layer height, or adaptive layer height where supported |
| Rough or uneven bottom face | The face that sits on the build plate | First-layer height or bed preparation problem | First-layer height and bed surface, not ironing |
| Rough curved or organic top | Rounded tops, sculpted shapes | Ironing is designed for flat surfaces and has little or no effect here | Layer height |
Seam marks and general wall roughness are not covered by the guidance this article relies on. If a seam is the visible problem, confirm that it is a seam and not layer stepping before changing layer height.
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Flat top surfaces: enable ironing
Prusa’s documentation describes ironing as a second infill pass at the same layer height. The nozzle runs across the top surface while it is hot, flattening raised plastic and using a small amount of filament to fill holes. It is aimed at flat top surfaces such as lids, badges, and nameplates. On round objects and organic shapes, it has little or no effect.
Ironing is a finishing pass, not a fix for bad geometry or poor calibration. Follow these steps:
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- Confirm the target is a flat, visible top. If the top is curved, ironing will not help.
- Enable ironing in your slicer’s print profile. Look for an “Ironing” group or setting in the print settings. The menu location varies by slicer and version, so search the settings for “ironing.” Some slicers mark it as experimental.
- Set the three tuning controls. Ironing flow controls how much plastic is extruded during the pass. Spacing controls the distance between passes, and it should be smaller than the nozzle diameter. For a 0.4 mm nozzle, that means a spacing below 0.4 mm. Speed should generally be slower than normal, though the sources do not give a universal number.
- Print a small test square. Change one control at a time and compare results. Keep the test small so each attempt is quick.
Use the test results to adjust flow:
- Grooves remain after ironing: the flow is likely too low.
- Excess plastic is pushed toward the edges: the flow is likely too high.
Ironing is sensitive to extrusion calibration. If the top is still rough after you have tuned flow, check your extrusion calibration before adjusting the other controls.
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Trade-offs of ironing
- Print time increases. Each ironed layer adds a pass.
- Edges can become slightly fuzzy. This is most noticeable when the flow is set high.
- Slow, low-extrusion ironing can cause heat creep or a clogged hotend on some machines. Prusa’s observations link this to PLA and warm ambient conditions. Watch for this on printers in warm rooms.
- Filament changes the result. PETG can stick to the nozzle more readily. Prusa reports good ironing results with PLA and ASA, with material-specific caveats, and poor results in its tests with wood-filled filament.
These are manufacturer observations, not guarantees for every printer or brand. Your filament’s recommended profile is the best starting point.
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Sloped and curved walls: lower the layer height
When the visible defect is stair-stepping on a slanted or curved side, ironing does not help, because the steps are on the walls, not the top. Layer height is the relevant setting. Smaller layers reduce the apparent step size and improve detail, but they increase the number of layers and the total print time.
Lower layer height also changes the solid-layer math. Prusa notes that low layer heights need more solid layers to keep the same top and bottom thickness. If you lower the layer height, check the top and bottom layer counts, or the equivalent shell thickness setting, so the top and bottom do not end up thinner than intended.
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Adaptive layer height
Where the slicer supports adaptive layer height, it can use thinner layers on steep sections and thicker layers on flat ones. This targets the stepping on angled surfaces without raising the print time for the whole part. Use your printer’s supported profile as the starting point rather than a single value taken from another machine.
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If the rough area is the face touching the build plate, inspect the first layer before changing any top-surface setting. Prusa identifies poor first layers as a common source of print problems. Its guidance cautions against squishing the first layer excessively to improve adhesion, because that causes other problems.
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Check these first:
- First-layer height, which should match your printer’s supported profile
- Bed levelling and bed cleanliness
- Whether the first layer looks uniform across the whole plate
Ironing is for top surfaces. It will not correct first-layer texture.
Diagnostic sequence
- Identify the rough face: top, sloped wall, or bottom.
- Match the defect: gaps on a flat top, steps on a slope, or first-layer texture.
- Confirm your printer, slicer, nozzle, and filament profile are set correctly.
- Change one relevant setting, such as ironing on a top, or layer height on a slope.
- Print a small test piece and compare it with the previous result before changing anything else.
Cura’s official quality-settings documentation groups settings such as print speed, nozzle temperature, and first-layer height under quality controls. That grouping reflects the same point: the right change depends on the defect, not on one universal value.
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