The surface quality of 3D printed parts

Surface quality of 3D printed parts cover

Source: 3Faktur, EAH Jena

The quality of the surfaces of industrial 3D printing technologies varies greatly. In addition to the 3D printing process, the geometry to be printed and its positioning in the printer also play a major role in the surface quality of the 3D printed object. In case of technologies that require support material, there are areas that require special attention, especially at the points of contact between support and the actual object.

We have compiled detailed information for you on the surface properties of the major industrial 3D printing technologies. Click on the respective technology to learn more.

Several 3D printing processes, including stereolithography (SLA/STL), digital light processing (DLP), two-photon polymerization (2PP) and continuous liquid interface production (CLIP) are all based on this principle of operation. Support structures are always necessary for these procedures.

The liquid raw material is cured by selective exposure at the specified areas. The above mentioned methods differed with regard to the exposure sources used (Stereolithography → Laser; Digital Light Processing → Projector) and the resolution in the Z direction (CLIP → no layers; all other methods layer thickness: 20 – 100 µm) or X-Y direction (2PP: resolution in the nanometer range).

Surface quality

The surface roughness in stereolithography varies greatly depending on the orientation in the printer. While the upper side is already in the low single-digit µm range without reworking at the Ra value, the underside is very rough due to the support structures scars.

However, the material (epoxy based) is relatively easy to rework. Since the material is largely non-porous, very good surface values can be achieved by blasting or manual grinding (see illustration for details).

Surface roughness Ra and Rz Stereolithography

Image: surface roughness Stereolithography
Source: 3Faktur; EAH Jena

Finishing Options

On the support side, the processing is usually done with sandpaper. In order to obtain homogeneous surfaces, the objects can also be blasted (usually using aluminum oxide).

Microscopic images of Stereolithography printed parts (bottom side without post processing)

Bottom side raw; Ra 13,3 µm / Rz 113,71

Microscopic images of Stereolithography printed parts (bottom side shot blasted)

Bottom side blasted (aluminum oxide); Ra 4,6 µm / Rz 29,8

Microscopic images of Stereolithography printed parts (bottom side shot grinded)

Bottom side blasted (aluminum oxide) and grinded; Ra 0,4 µm / Rz 3,3

Image: microscopic images of the bottom side of a stereolithography printed part.
Source: 3Faktur; EAH Jena; The part was printed on a Raplas 450 HD using the material RR60Cl (SLA detail resin).


The objects are largely non-porous and very good surfaces can be produced by repeated grinding. In addition to “normal” rapid prototyping applications, these objects can also be used for prototypes or for applications that require coating.

Layered structure (schematic)

Surface stereolithography schematic
  • X – Y plane: Surfaces printed horizontally to the building platform have a very good, smooth surface. An exception are the areas to which support structures are attached, where residues may be visible (not shown).
  • Z plane: The layers are perceptible through minimum inaccuracies during printing, or by the fact that transitions are not realized continuously, but only at intervals of one layer (usually ~50 – 100 µm) (Figure: right & left). These layers can largely be removed with (abrasive) finishing processes (red line).
  • Other characteristics: Since the printing process generally does not take place in a vacuum, small amounts of trapped air can build up. However, these are usually not visible to the naked eye.

Print sample

Sample print Stereolithography magnified
Sample print Stereolithography profile

Design: Thingiverse | LuluPaw

Print sample

This 4.5 cm tall owl figure was printed in standard grey stereolithography material. Even in the greatly enlarged image, the pressure layers are hardly visible. Only a few print layers can be identified.

The best known and most commonly used technologies are HP Multi Jet Fusion, Selective Laser Sintering, and Colorjet. In this technology, powdery starting materials are selectively bound. This can be done by a chemical process (gluing) like the Colorjet process or by a thermal process (SLS → Laser; HP Multi Jet Fusion → Infrared). With the exception of metal printing (SLM), support structures are not necessary for these forms of additive manufacturing, since the object is completely embedded in the material powder.

Surface quality

The surfaces of the objects are of good quality. Due to the elimination of the support structures, the surfaces are largely homogeneous. Depending on the material (powder grains of ∅ approx. 60 µm ), holes/pores occur on the object surface. This means that even during grinding, no completely smooth surfaces can be produced. However, processes differ, e.g. laser sintering produces more porous parts than the HP Jet Fusion process (More details: Laser sintering vs. HP jet Fusion).

Surface roughness of laser sintered parts - Ra and Rz
Surface roughness Ra and Rz Multi Jet Fusion

Image: surface roughness Laser Sintering & Multi Jet Fusion
Source: 3Faktur; EAH Jena

Finishing Options

Common post-processing methods are grinding, shot blasting or vibratory finishing (in particular SLS). This allows the surfaces to be smoothed, but the surface quality of liquid-based processes cannot be achieved. In laser sintering, creating an almost pore-free surface is only possible with great effort (vacuum infusions or a multi-stage process of surface filling with subsequent multiple grinding).

In the example below, laser-sintered parts were infiltrated with epoxy resin in a vacuum and then polished. A very good surface quality can be achieved by closing the pores. In most cases, however, this is practically not cost effective. If Ra values of 1 µm (+/-) are required, stereolithography or the Polyjet process are usually used.

microscopic image of the surface of laser sintering parts - raw

Laser Sintering | PA2200 (raw); Ra 13,1 / Rz 90,5

microscopic image of the surface of laser sintering parts - shot blasted

Laser Sintering | PA2200 (blasted with Aluminum oxide); Ra 6 / Rz 38,7

microscopic image of the surface of laser sintering parts - vacuum infiltrated and grinded

Laser Sintering | PA2200 (vacuum infiltrated and grinded); Ra 1,3 / Rz 9,3

Image: Microscopic images of laser sintered parts
Source: 3Faktur; EAH Jena; The parts weere printed on a EOS P390 with the material PA2200.


All typical applications of rapid prototyping as well as end-use parts (additive manufacturing). Laser sintered and Multi Jet Fusion parts are relatively cheap, very resilient and of high quality, and therefore often used for fully functional parts in end-use products.

Layered structure (schematic)

Laser Sintering 3D printing layer build-up schematic
  • X – Y level: No homogeneous surfaces possible, smallest pores are created by the powder grains from of the raw material.
  • Z plane: The same applies here as for the X-Y plane.
  • Other characteristics: Pores can be partially “closed” by infiltration. Grinding only brings a limited increase in quality.

Sample prints

Surface quality ColorJet sample print magnifiedSurface quality ColorJet (post-processed) sample print magnified

Design: Thingiverse | LuluPaw

Sample print Colorjet (top images)

The upper figure (owl, 4.5 cm) shows the Colorjet technology without finishing, the lower image shows a Colorjet print with surface finishing. The surface is basically “granular” due to the powder, but this effect can at least be improved by processing.

Oberflächenqualität Lasersintern Detailausschnitt
Oberflaecheneigenschaften Lasersintern Seite

Design: Thingiverse | LuluPaw

Print sample Laser Sintering

The surface in laser sintering is slightly finer, but the layers of the 4.5 cm large owl are still visible.

There are a variety of technologies that use the extrusion method. The best known are FDM/FFF (filament 3D printing), special extrusion processes e.g. fiber-reinforced systems (carbon/glass fibers), syringe-based systems (Bio-3D printers, food printers, concrete printers). Support structures may be necessary depending on the geometry of the part. The process works according to the following principle: a thermoplastic material is discharged through an extruder and hardens during cooling.

Surface quality

The quality of the surfaces is rather low. The outer layers (Z-direction) are strongly corrugated, but they are almost pore-free (in industrial, high-quality printers) and can be reworked to a high-quality level. The underside is usually very smooth in places without support, on the upper side the surface roughness is comparable to other 3D printing technologies (see data below).

In places with support material the surfaces are partly strongly impaired. However, some printers use soluble (water or other chemicals like limonene) support materials, which allows for significantly better quality.

Surface roughness Ra and Rz FDM

Image: Surface roughness FDM
Source: 3Faktur; EAH Jena

Finishing Options

For PLA and PA6/PA66, finishing is usually limited to the removal of support material. ABS can be reworked quite well and can be polished, blasted or tumbled.

Microscopic images of surfaces of an FDM printed part - raw

FDM | ABS (raw); Ra 8,8 / Rz 88,4.

Microscopic images of surfaces of an FDM printed part - grinded

FDM | ABS (grinded); Ra 2,4 / Rz 28,3.

Image: Microscopic images of FDM printed parts
Source: 3Faktur; EAH Jena; The parts have been printed on an Ultimaker 3 with the material ABS (Ultimaker).


The most common applications for extruded plastic objects are functional parts. The objects are only suitable for the production of moulds or for painting with great effort.

Layered structure (schematic)

FDM 3D printing layer build-up schematic
  • X – Y plane: The surface is less corrugated, but the individual layers are visible (from the running direction of the print head).
  • Z Layer: The layers can be differently pronounced, smooth surfaces in Z direction are possible by grinding, especially with ABS (red line).
  • Other characteristics: Gaps between layers are possible due to the process → Reduction of tensile strength in Z direction.

Sample prints

Surface of FDM prints magnified
Surface of FDM prints profile

Design: Thingiverse | LuluPaw

Sample print

The FDM technology produces clearly visible grooves. These can be reworked differently depending on the material. The PLA shown here can be post-processed to a limited extent. The ABS, on the other hand, can easily be mechanically and chemically refined.

The best known processes are Polyjet and Multijet Modeling (MJM). Light-curable polymers are applied to a work platform by a print head with several nozzles. The still liquid material is immediately cured by UV light. Support structures are always necessary for these procedures.

Surface quality

These technologies produce good to very good surfaces. The applied material droplets melt to form very low layer heights. This results in very homogeneous surfaces with barely perceptible layer thicknesses (15 – 30 µm). Here, too, support structures are necessary which impair the quality of the “affected” areas. This restriction no longer applies to 3D printers that use thermally soluble (3D systems) or water soluble (Stratasys, Keyence) support materials. By using material droplets, the deposit layers are also visible in the X-Y direction (direction of movement of the print heads).

Surface roughness Ra and Rz Polyjet

Image: surface roughness Polyjet
Source: 3Faktur; EAH Jena

Finishing Options

Removing the support structures is necessary for “normal” Polyjet printers. With water / thermal-soluble support, post-processing is usually not necessary. The techniques used are in particular blasting and grinding, where very good surface values can be achieved (see figure below).

microscop image of Polyjet 3D prints - raw

Polyjet | VeroBlack (raw); Ra 6 / Rz 29,1.

microscop image of Polyjet 3D prints - shot blasted

Polyjet | VeroBlack (blasted with aluminum oxide); Ra 3,7 / Rz 24,2.

microscop image of Polyjet 3D prints - grinded

Polyjet | VeroBlack (grinded); Ra 0,2 / Rz 1,7.

Image: microscopic images of Polyjet 3D printed parts
Source: 3Faktur; EAH Jena; The parts were printed on a Stratasys Objet 350 with the material VeroBlack.


Like Stereolithography, the surfaces are largely free of pores and can be further improved by repeated grinding. Therefore, the objects are also suitable for the production of original moulds in addition to the usual rapid prototyping applications.

Layered structure (schematic)

Polyjet 3D printing layer build-up schematic
  • X – Y plane: Minimal layers are created by the print head paths.
  • Z Layer: Minimal noticeable layers present can be smoothed out by ablation methods (red line).
  • Other characteristic: Layers are present at all levels (not shown).

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About 3Faktur: 3Faktur is a 3D printing service bureau. We are specialized in the production of plastic parts in low (rapid prototyping) or larger (rapid manufacturing) quantities. Get in touch.