Acetone Vapor Smoothing: Definition, How It Works, and Advantages

Acetone vapor smoothing is a process used to reduce the surface roughness of certain 3D-printed polymers, primarily for aesthetic reasons. Due to the nature of fused deposition modeling (FDM), which lays down discrete layers, the surface finish of parts is often very bumpy. This can be refined by using a smaller layer height, but this increases the print time and only goes so far. Acetone vapor smoothing dissolves the outermost layer of the print to smooth the surface, leaving behind a glossy finish. The acetone vapor smoothing method increases the aesthetic appeal of 3D printed parts and it’s faster than other surface smoothing processes.

This article will discuss acetone vapor smoothing, how it works, and its advantages.

What Is Acetone Vapor Smoothing?

Acetone vapor smoothing is a post-processing technique used to reduce the surface roughness of 3D printed parts. It is most commonly applied to ABS (acrylonitrile butadiene styrene) and ASA (acrylonitrile styrene acrylate) parts printed on FDM machines. The vapor fumes of acetone dissolve and smooth the part’s surface. FDM 3D printing creates very rough surfaces in the printer’s z-direction, so the parts often need post-processing. 

Which Types of 3D Printing Materials Are Compatible With Acetone Vapor Smoothing?

Acetone vapor smoothing works on any material that can be dissolved by acetone. Some filament types that don’t respond the same way to acetone may be damaged by the process or may remain completely unaffected. The five most common 3D printed materials which benefit from acetone vapor smoothing are:

1. ABS (acrylonitrile butadiene styrene)
2. ASA (acrylonitrile styrene acrylate)
3. PMMA (polymethyl methacrylate)
4. HIPS (high-impact polystyrene)
5. PC (polycarbonate) 

For more information, see our guide to 3D printing.

How Is Acetone Vapor Smoothing Work?

There are six key steps to the acetone vapor smoothing process:

1. Preparation

During preparation, sand the 3D printed part to remove any particularly coarse surfaces, including those with 3D printed supports. Use a clean file to ensure no foreign particles get lodged in the material. This surface preparation does not take long but is required to remove larger deformities. 

Evaluate how to suspend the part such that the acetone vapor contacts all surfaces that need smoothing. This usually means only the sides and top faces will be smoothed during a single session. Also, ensure that the part will fit inside the container with the lid closed. The part will need a base to rest on that will not dissolve in acetone. Metal foil is usually a good option. 

2. Acetone Vapor Generation

There are several ways to generate acetone vapors. The easiest way is to add some acetone to a container and cover (but do not seal) it. This method takes advantage of the fact that acetone quickly evaporates in the air. Make sure that the container is not also made of acetone-soluble material. Glass is usually best as it does not react to the vapor and it is transparent so you can see the part while the process runs. To improve the quality of this method, you can soak a paper towel with acetone and suspend it around (but not touching) the part. 

3. Object Suspension

Next, place the part into the container. The part must be suspended in the container such that it is not touching either the liquid acetone or the acetone-soaked paper. If it does touch, the part will dissolve quicker at the contact point. Seal the part in the container. 

4. Vapor Exposure

Leave the part in the container and monitor it continuously. There is no set timeframe or method of calculating how long the part might need to be in the container. This will depend on several variables including: the rate of acetone evaporation, the size of the container, the size of the part, and the initial surface roughness.

5. Smoothing Process

Once the liquid acetone has vaporized and started to dissolve rough surface features and layer lines, keep a close eye on the object to ensure ‘over smoothing’ doesn’t occur. This is why optically transparent containers are best. Proper observation will ensure a glossy finished product. 

6. Ventilation and Drying

The final stage of the acetone vapor smoothing process is ventilation and drying. Remove the container carefully to prevent contact between the paper towels and the 3D-printed part. Place it in an isolated, well-ventilated area so that any excess acetone can evaporate into the air. It may take anywhere from a few hours to a couple of days to dry out and harden completely. This stage is important to ensure the finished product will have a smooth, rigid finish that is ready to be handled and used. 

What Are the Advantages of Acetone Vapor Smoothing in 3D Printing?

Acetone vapor smoothing is a good option for several reasons. The advantages are discussed below:

1. Surface Quality

Acetone vapor smoothing improves the surface quality of printed parts. Naturally, 3D-printed parts have rough surfaces because they are made in layers. Acetone vapor smoothing is an effective process of reducing surface roughness and improving surface quality, mainly for aesthetic purposes. 

2. Time and Cost-Efficiency

Compared to other post-processing methods that use sandpaper, heat guns, or filler material, acetone vapor smoothing is quicker and cheaper. Those other methods concentrate effects on only one area at a time, so they’re more labor-intensive in general. The acetone vapor, by contrast, affects all areas of the model equally. Thus, acetone vapor smoothing can actually boost your productivity.

3. Smoothing Complex Geometries

Acetone vapor smoothing has advantages over other methods because it can reduce the surface roughness of complex geometries evenly. Other methods have trouble adding or removing an even layer of material, especially over complex geometry. 

4. Strength and Integrity

Prior to acetone vapor smoothing, FDM prints are very anisotropic. This means that their mechanical properties differ when loaded in different directions, and it’s considered a major problem with FDM 3D printing. The vapor smoothing, however, helps to even that directionality out, putting the parts closer to isotropy. In short, the acetone vapor smoothing creates more bonds in the z-axis (perpendicular to the print bed) but decreases strength in the x-axis and y-axis (parallel to the print bed). Such can be advantageous if your item is likely to see z-axis loads. 

How Does Acetone Vapor Smoothing Affect the Thickness or Material of the 3D-Printed Object?

Acetone vapor smoothing has no effect on the overall thickness of the 3D-printed object. The process only smoothes the item’s surfaces. This does not reduce the thickness or overall geometric parameters of the finished product. 

What Are the Best Methods for Applying Acetone Vapor Smoothing to 3D-Printed Objects?

The best method for applying acetone vapor smoothing depends on several factors, including the time required to complete the process and the size of the part. In general, there are three prominent methods used to apply acetone vapor to 3D-printed objects:

1. One method is to apply acetone using a paintbrush. However, this takes more manual work and is less likely than other methods to give you a completely even and glossy finish. 
2. The second method is submerging the part in the acetone. This process, however, generates unpredictable results. 
3. The third method is to use an acetone steam bath where the acetone is either heated gently to create vapor or allowed to evaporate naturally. This final method is considered the best way to create an even, glossy finish. 

Can 3D-Printed Edges Be Improved With Acetone Vapor Smoothing?

Yes, any edge of a 3D-printed part, as long as it’s printed in a material susceptible to acetone, can be improved using acetone vapor smoothing. Parts with large layer heights see the greatest benefits. Parts with smaller layer heights or which are printed via different 3D printing techniques will receive less benefit but are still likely to come out smoother than before. 

Is Acetone Vapor Smoothing Better for Certain 3D-Printed Materials?

Yes, some materials benefit from acetone vapor smoothing while others do not. The viable materials are: ABS, ASA, PMMA, HIPS, and polycarbonate. On the other hand, some will be degraded by exposure to acetone while others will be entirely unaffected. Examples of materials that do not benefit from this post-processing include: PLA, PETG, Nylon, and TPU. 

What Are the Differences Between 3D Printing Post-Processing Methods and Acetone Vapor Smoothing?

Acetone vapor smoothing is a form of 3D printing post-processing. Others include the likes of: sanding, sandblasting, using XTC-3D, using 3D gloop, using Polymaker Polysmooth PVB filament, chemical smoothing, and using a heat gun. These post-processing methods differ in application and target materials. For example, Polymaker Polysmooth and chemical smoothing are similar to acetone vapor smoothing as they all use a chemical reaction to dissolve and smooth the outer layer. The difference is that Polymaker Polysmooth uses a patented filament and chemical exclusive to that filament, and chemical smoothing uses a different chemical such as ethyl acetate to smooth PLA. 

Sanding and sandblasting also differ from acetone vapor smoothing. They are purely abrasive techniques that erode the high ridges of the part, leaving a smooth surface. XTC-3D and 3D gloop, meanwhile, use a filler material to build up the outer surface and give it a smooth and glossy appearance. 

What Are the Differences Between Acetone Vapor Smoothing and Vapor Smoothing PLA?

Acetone vapor smoothing and chemical smoothing of PLA are the same methods in principle. They both partially dissolve the surface layers of the material. However, PLA (polylactic acid) plastic responds to ethyl acetate rather than acetone. Acetone won’t create the proper effect on PLA and ethyl acetate won’t do the trick on ABS and other plastics that respond to acetone. To learn more, see our guide on Vapor Smoothing PLA.

Summary

This article presented acetone vapor smoothing, explained it, and discussed how its works and its advantages. To learn more about copper, contact a Xometry representative.

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