FDM 3D print quality: the settings for a smooth, flawless part

A good FDM part does not come from one magic setting. It comes from a dozen parameters, checked in the right order, on a machine in good condition and with healthy filament. Changing everything at once leads nowhere: you no longer know what helped and what made things worse.

Here are those settings, from the most fundamental to the finest. They apply to every FDM printer, whatever the brand. The values given are starting points, to adjust to your machine and your spool.

1. Start with the filament: dry, or nothing

This is the most common cause of surface defects, and the most often overlooked. Filaments absorb moisture from the air. In the nozzle, that water turns to steam abruptly. The result: bubbles and craters on the surface, popping sounds during printing, a grainy and dull finish, and often stringing.

Not all materials react the same way to moisture:

• PLA: not very sensitive, but a spool left open for months eventually degrades.
• PETG and TPU: sensitive. A few weeks in open air are enough for bubbles to appear.
• Nylon and polycarbonate: very sensitive. They are almost always dried before printing.

Drying for several hours at a moderate temperature, in a dedicated dryer, solves the problem. Temperatures and durations depend on the material: follow the spool manufacturer's recommendations. Then store spools in airtight boxes or bags with desiccant.

2. A calibrated, clean machine

Before touching the slicer, check the basics:

• The build plate must be clean and degreased (isopropyl alcohol). A greasy plate ruins the first layer, and the first layer conditions everything else.
• The nozzle wears out, especially with carbon- or glass-filled filaments. A worn or partly clogged nozzle produces uneven extrusion and marked walls.
• Flow calibration prevents over-extrusion, which creates ridges, and under-extrusion, which leaves gaps between lines.
• Pressure advance calibration (called flow dynamics on Bambu Lab machines) prevents excess material in corners and gaps when exiting a turn.

On Bambu Lab machines, some of these calibrations run automatically. That does not replace checking the profile of each new spool, especially from another brand.

3. Layer height: the first visual lever

Layer lines are the signature of FDM. You do not remove them, you reduce them.

Layer height (0.4 mm nozzle)	Result	Use
0.28 mm	Clearly visible lines	Draft, hidden part
0.20 mm	Standard	Functional part
0.12 to 0.16 mm	Subtle lines	Visible part, gentle curves
0.08 mm	Very fine	Small details, at the cost of much longer print times

On a part with gentle curves, variable layer height (adaptive layers) is a good compromise: thin layers in curved areas, thicker layers on straight walls.

4. Speed and acceleration: slow outside, fast inside

Recent printers print very fast. That is an asset for infill, much less so for visible walls. Vibrations and sudden changes of direction leave ripples (ringing) on the surface.

Good practice: lower the speed and acceleration of outer walls, and keep high values for inner walls and infill. Print time increases only moderately, and the visible surface improves clearly.

5. Temperature and cooling

Nozzle temperature is chosen within the range printed on the spool. Too hot, the material runs, strings and forms blobs. Too cold, layers bond poorly and the surface turns matte and rough. A temperature tower, printed once per new spool, gives the right value in a few minutes.

Cooling depends on the material:

• PLA: strong part cooling after the first layers. It sets each layer quickly and cleanly.
• PETG: moderate cooling. Too much cooling weakens layer adhesion.
• ABS and ASA: low cooling, and printing in an enclosure to avoid warping.

6. Walls, top layers and seams

Wall count. With only two walls, the infill pattern can show through the surface. Three walls or more give a more even surface and a stronger part.

Top layers. Too few solid top layers, and the top surface bulges over the infill (pillowing). Aim for at least 5 top layers on a visible surface, more with thin layers.

Ironing. On flat top faces, the nozzle passes over the last layer again while extruding very little material. The surface becomes noticeably smoother, at the cost of a few extra minutes of printing.

Seams. Every layer starts and ends somewhere, and that point leaves a small mark. Place it on an edge or on the back of the part rather than at random. Recent versions of Bambu Studio also offer a scarf seam, which makes it almost invisible on curved surfaces.

7. Orientation and supports: think about the visible face

Orientation matters as much as settings:

• The most visible face should be vertical (fine, regular lines) or placed on the build plate (flat, clean surface).
• Supports always leave a mark. Place them on hidden faces, and use a support interface for a cleaner separation.
• Overhangs beyond roughly 45° degrade without support. A slight change of orientation is sometimes enough to avoid them.

If your file comes from CAD software, our guide to preparing an STL file also avoids visible facets caused by a coarse export.

The limits of FDM, even well tuned

A perfectly tuned FDM printer produces clean, regular parts, but not a mirror finish. Layer lines remain perceptible to the touch. To go further, two options:

• Resin, which gives a smooth surface and fine detail straight off the printer. See our FDM or resin comparison.
• Post-processing: sanding, primer, paint on an FDM part.

To go further on the process itself, our FDM page covers how it works and its materials. And if you do not have a printer at hand, you can also get your part quoted.

Frequently asked questions

Why does my 3D print have bubbles?

In the vast majority of cases, the filament is wet. Absorbed water turns to steam in the nozzle and creates bubbles, craters and popping sounds. Dry the spool following the manufacturer's recommendations, then store it with desiccant. An excessive nozzle temperature can make it worse.

Which layer height should I choose for a smooth part?

With a 0.4 mm nozzle, 0.12 to 0.16 mm is a good compromise between finish and print time for a visible part. Below that, the visual gain becomes small compared with the extra time.

How do I get rid of layer lines in FDM?

You can reduce them (thin layers, moderate outer wall speed, good orientation) but not remove them at the printing stage. For a perfectly smooth surface, you need post-processing (sanding, primer) or resin printing.

Does printing slower improve quality?

Mainly on outer walls. Lowering the speed and acceleration of those walls reduces ripples and surface defects. Slowing down infill usually brings no visible benefit.

What is ironing for?

Ironing makes the nozzle pass over the last top layer again while extruding very little material. It makes flat top faces noticeably smoother. It has no effect on vertical walls.