How to Use Ironing for Smoother 3D Print Tops

What ironing does

Standard FDM top layers leave parallel extrusion lines and tiny valleys where the toolpath turns. Ironing is a slicer setting that adds a second finishing pass over the flat top surface. The nozzle stays at the same Z-height, moves slower, and extrudes only 5% to 15% of normal flow. The heat from the nozzle tip and that thin stream of plastic smooth out the ridges without adding height to the part.

The result is a more uniform satin or gloss finish. It can make badges, lids, and enclosures look finished without sanding or vapor smoothing.

How the settings work

Ironing changes more than just flow. Speed drops to 10-30 mm/s, line spacing tightens to 0.08-0.15 mm, and the toolpath usually switches to a cross-hatch or perpendicular pattern. The printer does not raise the Z-axis after the final top infill. Instead, it runs the ironing pass directly on that same layer.

When to use it

Ironing works best on flat horizontal planes. Large badges, coasters, lids, and mechanical baseplates are ideal. Recessed debossed text on a flat surface also benefits.

Avoid ironing on curved or organic shapes, shallow stepped roofs, fine raised text, small isolated pins, and tall narrow columns. Those geometries either do not need it or can be damaged by the extra heat and slow pass.

Starting settings by material

PLA is the easiest material to iron. Try 10%-12% flow, 20-25 mm/s, and 0.10 mm line spacing with full fan cooling.

PETG is stickier. Drop flow to 5%-8%, slow to 15-20 mm/s, and reduce fan to 30%-50%. If the nozzle picks up blobs, lower flow a little more.

ABS and ASA need heat balance. Use 8%-10% flow, 20-25 mm/s, and 0.10-0.15 mm spacing. Keep fan low or off inside an enclosure. Too much heat in one spot can warp the part.

Common problems

Rough lines remain: increase flow by 2%-3% and tighten line spacing to 0.08 mm. Check extrusion multiplier and nozzle calibration.

Blobs or raised ridges: flow is too high. Drop flow by 3%-5%, increase the ironing inset to 0.30-0.35 mm, and clean the nozzle tip.

Edge lip bulge: increase inset and verify outer wall flow and pressure advance.

Surface smearing: speed up the ironing pass by 5 mm/s, drop nozzle temp by 5 degrees, and confirm cooling is running during top layers.

Nozzle dragging or gouging: add more solid top layers, reduce flow slightly, and recheck bed leveling and Z-offset.

Testing workflow

Print a small flat calibration tile. Examine it under low-angle light. Change one setting at a time. Filament brands, nozzle wear, and motion systems all change the outcome, so your best numbers will differ from someone else's.