Q2
Ironing Function: Even Beginners Can Smooth the Top Surface of Models
The Ironing Function in QIDI Studio effortlessly eliminates tiny striations on your model's top surface. After printing, the nozzle moves like an electric iron, slowly re-melting and flattening filament to fill gaps and create a perfectly smooth finish. Ideal for flat surfaces where aesthetics matter, it's an easy-to-enable feature for achieving professional-quality results on your 3D prints.
Ironing is a second, near-empty pass the nozzle makes over a finished top layer. It runs slowly, extrudes only a small percentage of normal flow, and spaces its lines far closer than a normal infill, so the hot nozzle flattens curled plastic and fills the gaps between top-layer lines. The result is a glassy flat top at the cost of extra print time.
Is your model generally good, but let down by tiny striations that make the top surface less than perfect? The Ironing Function in QIDI Studio offers a targeted solution to this issue.
After the top layer of the model is printed, the nozzle continues to move back and forth at an extremely slow speed—just like ironing clothes with an electric iron. Through this action, the small amount of extruded filament is melted and flattened, filling in the gaps between the lines to create a much smoother top surface. The Ironing Function is ideal for models with flat top surfaces, especially when high aesthetic standards are required. However, it is of little use for models with curved tops, pointed tops, or intricate details; in such cases, it will only increase printing time unnecessarily.
Schematic Diagram
Comparison Before and After Ironing:
Ironing Settings at a Glance
Every ironing setting maps to one visible symptom on the finished top surface. This table is the fastest way to go from "what I see" to "what to change".
| Setting | What it controls | Typical starting point (0.4 mm nozzle) | Symptom and the fix |
|---|---|---|---|
| Ironing Type | Which layers get an ironing pass | Top Surfaces | Print time ballooned on a stepped model — switch to Topmost Surface |
| Ironing Pattern | The path shape of the ironing pass | Rectilinear | A visible dot or knot in the centre of a round top — that is Concentric; switch to Rectilinear |
| Ironing Speed | Nozzle travel speed during the pass | 30 mm/s (QIDI Studio default), lower for a better finish | Streaky, unevenly melted surface — halve the speed before touching anything else |
| Ironing Flow Rate | Extrusion during the pass, as a percentage of normal flow | Around 10–15% is where mainstream slicer profiles sit | Ridges and material piling up — lower it. Grooves still visible between lines — raise it. |
| Ironing Line Spacing | Distance between adjacent ironing passes | 0.1–0.15 mm; always keep it below the nozzle diameter | Gaps not closing — reduce spacing. Nozzle dragging plastic around — raise spacing or lower flow. |
| Ironing Inset | How far the ironing area stops short of the outer contour | Start at 0, increase toward ~1 mm if edges build up | A raised lip or bead around the perimeter of the top face — increase the inset |
Two of these interact and cause most bad results: flow and spacing must be tuned together. Halving the spacing doubles how many times the nozzle passes over the same square millimetre, so the same flow percentage now deposits twice as much plastic there. If you tighten spacing, drop the flow with it.
Operation Guide
1. Enable the Ironing Function
The Ironing Function is disabled by default in QIDI Studio. You can enable it by modifying the Ironing Type in the "Quality" section.
There are two commonly used Ironing Types, with the following differences:
- Top Surfaces: All top surfaces of the model will be ironed.
- Topmost Surface: If the model has varying heights, only the highest layer (i.e., the last layer printed) will be ironed.
Ironing Top Surfaces vs Topmost Surface: which one to choose
This is the single most common point of confusion, and the answer depends entirely on whether your model has more than one flat level. A slicer in this family also exposes a third, rarely used option — All solid layers — which irons every solid layer inside the part, not just the visible ones.
| Ironing Type | What gets ironed | Best for | Cost |
|---|---|---|---|
| Top Surfaces | The last layer of every flat area, at every height in the model | Boxes with recessed pockets, stepped bases, nameplates with sunk lettering, anything with several visible flat levels | Highest print-time penalty of the two common options |
| Topmost Surface | Only the single highest layer of the whole object | Lids, coasters, plaques, tiles — one flat face on top and nothing else that shows | Minimal; usually only a few extra minutes |
| All solid layers | Every solid layer, including internal solid infill | An experimental case: 100% infill parts printed in transparent filament for optical clarity | Very large time increase; not for general use |
A worked example makes the difference concrete. On embossed text lying parallel to the bed, Topmost Surface irons the tops of the letters only and leaves the background field untouched; Top Surfaces irons both the letters and the recessed background between them. If the background is visible in the finished part, you want Top Surfaces.
2. Set Key Parameters
Ironing Pattern
There are two patterns available: Rectilinear and Concentric.
- Rectilinear: The more widely used option, with strong versatility.
- Concentric: May deliver better ironing results on the edges of the top surface, but tends to leave a small dot in the center of the model.
Concentric vs Rectilinear Ironing: the practical difference
| Aspect | Rectilinear | Concentric |
|---|---|---|
| Toolpath | Straight parallel lines sweeping across the surface | Closed loops following the outline, working inward |
| Edge quality | Good; the inset setting handles most edge buildup | Often better, because the path runs parallel to the contour |
| Centre of the surface | Clean and even | Tends to leave a small dot or knot where the last loop closes |
| Irregular or multi-island shapes | Handles them predictably | Path quality degrades as the outline gets complicated |
| Light reflection | Directional; the surface can show faint striping in raking light | Circular sheen, which some people prefer on round parts |
| Use it when | Default choice for almost everything | Simple round or ring-shaped tops where edge finish matters most |
Ironing Speed
Refers to the moving speed of the nozzle during ironing, with a default value of 30mm/s. As the saying goes, "slow work yields fine results"—a slower speed usually leads to better ironing performance.
Ironing Flow Rate
Refers to the filament extrusion rate during ironing, and this value is relative to the flow rate used for normal printing. If you notice material buildup after ironing, reduce the flow rate; if gaps fail to be filled, increase the flow rate appropriately.
Because ironing flow is a percentage of normal flow, it is indirectly tied to layer height: a lower layer height means less volume extruded per millimetre of travel, so the same percentage delivers less plastic and may need to be raised. Ironing is also unusually sensitive to extruder calibration — if your flow multiplier is off, the ironing pass is where you will see it first, as either shiny unfilled grooves or plastic being dragged to the edges.
Ironing Line Spacing
Typically, the smaller the distance between ironing paths, the better the ironing effect. However, if the flow rate is too high and the spacing is too small, it may cause over-extrusion—ruining the surface finish or even scraping the already printed parts.
The governing rule is that spacing should stay below the nozzle diameter, which is what makes ironing work at all: the nozzle physically passes over the same spot several times, and each pass irons the ridge left by the last one. With a 0.4 mm nozzle, that puts the useful window at roughly 0.1–0.2 mm. The PrusaSlicer ironing documentation and the OrcaSlicer wiki entry on ironing both state the same constraint.
Ironing Inset
This value represents the distance between the ironing area and the contour boundary. Adjusting it to an appropriate value can prevent material buildup at the edges.
What ironing inset does, in one sentence: it stops the ironing toolpath short of the perimeter so the extra plastic has somewhere to go other than over the edge. Set to 0, the ironing path starts directly at the perimeter wall, and any surplus material gets pushed outward into a raised lip you can feel with a fingernail. Raising the inset toward 1 mm pulls the path inward and leaves that border alone. The trade-off is that a large inset leaves a narrow un-ironed band around the top face, which can be more visible than the lip you were trying to remove — so raise it in small steps and stop as soon as the edge bead disappears.
How Different Filaments Behave Under the Iron
Ironing settings are not material-specific in the slicer, but materials do not respond identically to a hot nozzle dragging across them.
| Material | How it irons | What to watch |
|---|---|---|
| PLA | Irons very cleanly; the easiest material to get a flawless top from | Most prone to heat creep during long ironing passes, because its glass transition is only around 60–65 °C. Make sure hotend cooling is working before ironing a large flat area. |
| PETG | Irons well | Higher tendency for filament to stick to and accumulate on the nozzle, then drop back onto the print as a dark blob |
| ASA / ABS | Irons very well and produces particularly smooth top surfaces | Needs a stable chamber temperature; treat ironing as one more reason to print these enclosed |
| TPU and other flexibles | Difficult | The nozzle-sticking problem of PETG, much more pronounced |
| Wood-filled and other composites | Poor results are common | Filler particles do not reflow like neat polymer, so the surface stays textured |
If you are choosing a filament specifically for a flat, showable top face, matte PLA is the forgiving option and the rest of the filament range is worth checking against the notes above. For transparent parts, the interaction is different again — see our notes on printing with transparent filaments.
The Real Costs of Ironing
Ironing is not free, and knowing the three costs up front stops most disappointment:
- Print time. The ironing pass covers the same area as the top layer but at a fraction of the line spacing and a fraction of the speed. On a large flat top it can add a noticeable block of time; the slicer's preview will tell you exactly how much before you commit.
- Heat creep risk. Extrusion during ironing is slow and small, so filament sits in the hot zone far longer than usual. On a big surface this can soften filament above the heatbreak and cause a jam. If you iron large areas regularly, keep an eye on it and make sure the hotend fan is clean.
- Slightly softer edges. The toolpath is planned for a tiny extrusion, but the nozzle is still physically 0.4 mm wide, so a little plastic bleeds past the boundary. Sharp top edges come out marginally rounded. The inset setting manages this, it does not eliminate it.
Best Practices for Using the Ironing Function
To achieve optimal ironing results, remember these key points: use a slow speed, set narrow line spacing, and fine-tune the flow rate based on actual conditions. When you need to print a model with a flawless "ceiling" (top surface), don’t hesitate to try the Ironing Function!
Three additions worth building into your workflow:
- Tune on a test tile, not on the real part. A 40 × 40 × 3 mm plate takes minutes and shows every ironing defect at full size.
- Consider flipping the model instead. A first layer printed against a smooth PEI sheet is usually flatter and glossier than any ironed top surface, and costs nothing in print time. If the showable face can go on the bed, put it there.
- Fix the top layer first. Ironing masks a bad top surface; it does not repair one. If the top layers are already gappy or pillowing, add a top layer or two and check your top infill before turning ironing on. Our guide to reducing visible layer lines covers the settings that matter, and how to smooth the top layer of 3D prints compares ironing against the alternatives.
Hardware matters here too, but less than people expect: ironing quality depends far more on consistent extrusion and a flat bed than on raw speed. A rigid machine with a well-calibrated extruder — such as the QIDI Plus 5 or any of the current QIDI 3D printers — gives ironing a clean top layer to work with, which is most of the battle.
Frequently Asked Questions
What is ironing inset in a slicer?
Ironing inset is the distance the ironing toolpath keeps away from the outer contour of the top surface. At 0 mm the pass runs right up to the perimeter and can push surplus plastic over the edge, leaving a raised lip. Increasing the inset moves the pass inward so the edge is left untouched.
Concentric or rectilinear ironing — which is better?
Rectilinear is the better default. It handles complex and multi-island top surfaces predictably and leaves an even centre. Concentric can produce a cleaner edge on simple round tops, but it tends to leave a small dot in the middle where the innermost loop closes, so it is a special case rather than a general choice.
What is the difference between ironing top surfaces and topmost surface?
Top Surfaces irons the last layer of every flat area in the model, at every height. Topmost Surface irons only the single highest layer of the whole object. On a model with one flat top they produce the same result; on a stepped model, Topmost Surface leaves the lower flat areas un-ironed and finishes much faster.
Why does my ironed surface have ridges or scrape marks?
Too much material for the spacing you set. Either lower the flow rate or widen the line spacing — and if you recently tightened spacing without lowering flow, that is almost certainly the cause. Scrape marks specifically mean the nozzle is meeting plastic that is already above the intended height.
Why are there still gaps after ironing?
Not enough material, or the pass is moving too fast to reflow what is there. Raise the flow rate in small steps first; if the surface still shows grooves, reduce the ironing speed. Very low layer heights need proportionally higher flow, because the percentage is relative to a smaller normal extrusion.
Does ironing work on curved or angled surfaces?
No. Ironing only acts on flat areas parallel to the build plate. On spheres, organic models or angled faces it has essentially no effect and simply adds print time. For those surfaces, the answer is sanding and polishing or a finer layer height.
Can ironing clog my hotend?
It raises the risk on long passes. Because ironing extrudes very slowly, filament dwells in the heat zone much longer than usual, which is the classic setup for heat creep — especially with PLA in a warm room. It is not a common failure, but if you iron large flat areas routinely, keep the hotend cooling fan and its duct clean.
