How to Get Smooth 3D Prints・Cults

Smooth surface finish is one of the most required aspects of a 3D print, but it’s not only an aesthetic need: it happens very often that smoothness is a functional requirement for the end users.

Applications in which smoothness may be a functional requirement include mating parts, moving parts, stress/load-bearing surfaces, etc.

Below you will find the list of the 3 key factors for ensuring smoothness of your finished 3D printed parts, suggested by the engineers from Xometry, the marketplace for on-demand 3D printing with more than 2.000 manufacturers in Europe.

Smooth 3D Prints: the best technologies

Because of the layer by layer printing involved in FDM printing and the diameter of the nozzle, FDM doesn’t always produce a very smooth surface finish. However, modern industrial FDM machines are capable of much finer surfaces. SLS, MJF, and DMLS produce a grainy surface as a result of the powdery nature of the raw materials used in these technologies. Regardless of 3D printing technology, a smooth surface can always be achieved in printed parts, using post-processing operations.

There are several 3D printing technologies capable of producing smooth as-printed parts. Those are explored below.

SLA 3D printing

Stereolithography 3D printing produces parts with the highest accuracy and smoothest surface finish among all 3D printing technologies. Although it is a layer-by-layer process, the raw material is usually in resin form and solidifies to give a smooth surface.

Polyjet 3D printing

Like SLA, Polyjet prints photopolymers. Most Polyjet parts are ready to use as-printed in terms of look and feel. The main reason for this smoothness is the combination of ultra-thin layer printing and high-quality resin.

Carbon DLS

Carbon DLS uses resin materials like polyurethane. The surface finish of the 3D part produced with this method is as smooth as glass. This process produces impeccable parts that can replace prototypes from MJF or SLS. In addition to a high-quality surface finish, Carbon DLS produces external and internal details perfectly.

Smooth 3D Prints: the best materials

Material consideration for smoothness typically goes together with printing process consideration, as, in most cases, the process is a far more significant factor. Thermoplastics, thermosetting resins, photopolymers, and polyurethane are typically 3D printing materials with a smooth surface finish.

But it is important to consider not only smoothness but also strength, heat resistance and accuracy for making the best choice.

Smooth 3D Prints: post-processing operations

Post-processing is the most effective way of guaranteeing a smooth surface finish in 3D printing. In most cases, post-processing can be used to achieve this result, even if the technology or the material are not so performative.

It is important to consider the geometry and the material of our 3D print for choosing the right post-processing method, because it will deliver different textures and appearances.

Bead Blasting

The bead blasting technique involves spraying a pressurized stream of tiny beads of media (plastic or glass) from a nozzle onto the surface of the part. This removes the layer lines leaving a smooth finish. In addition, the end product resembles a uniform matte finish. One of the advantages of bead blasting over sanding is speed. The process takes about 5 to 10 min for a part. However, the duration will depend on the part size. Another advantage of bead blasting is the preservation of the part’s dimensions.

Comparison of MJF Nylon PA12 parts: as printed (left) vs. bead blasted (right)

Vapour Smoothing

The industrial vapour smoothing device operates through a multistage process. It lowers the pressure within the sealed chambers containing the 3D printed parts. Then, a heated tray at the bottom receives the pumped solvent, turning it into vapour.

An air-circulation system pulls the resulting vapour and circulates it around the surface of the part, causing condensation on the surface. This melts away the surface of the printed part, leaving a smooth surface. This process takes about three hours.

Vapour smoothing is commonly applied in consumer products but cannot accommodate more materials like sanding or bead blasting.

Comparison of MJF Nylon PA12 parts: as printed (left) vs. black spray painted and vapour fused (right)

Tumble Finishing

The tumble finishing technique, also known as tumbling or rumbling, is usually used on relatively small parts. It is very effective for parts that contain a high percentage of metal powder.

In just an hour of polishing, the smoothness of metallic prints can be exponentially increased. The tumbling process uses a horizontal barrel filled with parts, media, water, or any other materials. A vibrator rotates the barrel, causing the media (stones) to continuously brush the parts and progressively smoothen them.

Comparison of SLS Nylon PA11 parts: as printed (left) vs. tumbled finished (right)

Sanding and polishing

Sanding is the process of progressively removing a very thin layer of material to expose a smoother one underneath. A rough surface simply means that some points on the surface are more elevated than others. Sanding is the process of evening out the surface using relatively rough materials such as sanders or grinders.

It can be carried out by hand or with the use of belt sanders and is done progressively. Sanding is most often paired with polishing.

One of the shortcomings of sanding is the difficulty in smoothening small, intricate geometries. Also, sanding may also affect a part’s dimensions. When very tight tolerances are required from the 3D parts, sanding may not be the best option.

Comparison of post-processing options for a smooth surface finish in 3D printing

Are you interested in testing the most effective method to achieve a smooth surface for your 3D prints? Feel free to upload your Craftez3D file on Xometry’s Instant Quoting Engine, select the technology, the material and the finishes you’re looking for and receive an immediate quotation.