How To Smooth 3D Prints: 5 Effective Strategies

FDM printers allow you to create decorative objects and collectibles, but they may not have the desired visual appeal.

This is where smoothing steps in. This procedure refers to diminishing printing defects and creating a smoother, more aesthetic surface.

Depending on the material and purpose, you can smooth 3D prints with acetone or other chemical vapors. Sanding is a common method that works well on most filaments, or you could use fillers and primers to mask small defects. Heat smoothing also works with some materials, but it can be hard to achieve.

5 Ways To Smooth 3D Prints

Smoothing 3D prints can be tedious, but the task is typically straightforward.

Here are the most common methods you can use.

1. Sanding

Sanding the surface of the print with increasingly fine sandpaper can help remove rough edges and imperfections.

This is a common and effective technique regardless of the material the prints are made of. To sand your 3D prints:

1. Start with a coarse-grit sandpaper, around 80 to 120 grit. This will help remove the outer layer of the print and any rough edges or bumps. Sand the print in a circular motion to ensure a uniform finish. Apply even but not excessive pressure as you sand to avoid damage to the print.
2. Switch to a finer grit, such as 220 to 320 grit. This will help remove any remaining roughness and scratches left by the coarse sandpaper.
3. Finally, use the finest grit sandpaper, around 400 to 600 grit, to create a smooth finish. This will help remove any remaining scratches and give the print a polished appearance. After sanding, wipe the print with a soft cloth or a damp paper towel to remove any dust or debris.

It’s important to note that sanding can be a time-consuming process, especially for larger prints.

Be patient as you work through each grit and don’t lose focus, or the results may not be as expected.

2. Chemical Smoothing

Chemicals, such as acetone and tetrahydrofuran, can be used to smooth the surface of prints made from ABS, PLA, and other similar materials.

This is achieved by exposing the print to chemical vapors, which melt and smooth the surface of the plastic, or through direct contact and immersion.

The secret to chemical smoothing is choosing the appropriate solvent. For example, acetone is used to smooth ABS, and tetrahydrofuran (THF) is used to smooth PLA.

It’s important to use the correct solvent for the material your print is made of, or the method won’t work.

To smooth the print by immersion: 

1. Choose a container that is large enough to hold the print and the solvent. The container should have an airtight lid to prevent the chemical from evaporating too quickly. It goes without saying that it should be made of a material that is resistant to the solvent you will be using.
2. Place the print in the container and make sure it is fully submerged in the solvent.
3. The length of time it takes for the solvent to work will depend on the size and complexity of the print, as well as the strength of the solvent. As a general rule, you should leave the print in the solvent for at least eight to 12 hours. Once the time lapses, remove the part and rinse it thoroughly with water to remove any remaining solvent. Dry it with a clean cloth or paper towel.

If the method worked, the surface of the print should be smoother and shinier. If the results are not satisfactory, you may need to repeat the process with a stronger solvent or for a longer period of time.

Keep in mind that chemical smoothing can be dangerous and should be done with caution. Always wear protective gloves and work in a well-ventilated area.

Follow the manufacturer’s instructions for handling and disposing of the solvent.

3. Heat Smoothing

This method involves using a heat gun or other heat source to slightly melt the surface of the print, resulting in a smoother surface.

It is more straightforward than sanding or chemical smoothing, but it requires some practice and great care to avoid damaging the print.

Heat smoothing is commonly used for ABS prints. The lower melting point of the material makes it easy to diminish printing defects.

However, remember that excessive heat can cause the filament to warp, deform, or even catch fire. It’s always a good idea to test the method on a small filament sample or a test print before attempting to smooth your final item.

Due to the higher melting point of PETG, PLA, and nylon, heat smoothing is typically ineffective for this filament type.

4. Fillers and Primers

Fillers and primers can be used to fill in gaps and imperfections on the surface of the print, resulting in a smoother finish.

These materials can be sanded and painted over for an even smoother appearance, but the method is laborious. This method is best used for TPU and ABS.

To smooth the print: 

1. Sand the surface to remove any bumps, ridges, or layer lines. Use fine-grit sandpaper (around 220 grit) to sand the surface of the print until it is smooth.
2. Apply a thin layer of filler to the surface of the print using a spatula or scraper. Filler can be a type of putty, spackle, or body filler. Spread the compound evenly across the surface of the print, making sure to fill in any holes or gaps. Allow the product to dry according to the manufacturer’s instructions.
3. Once the filler has dried, use sandpaper to sand the surface of the print again. Start with coarse-grit sandpaper (around 120 grit) and work your way up to fine-grit sandpaper (around 400 grit) until the surface is smooth and free of imperfections.
4. Apply a layer of primer to the surface of the print using a brush or spray can. This helps to create a smooth surface for paint or other finishes to adhere to. Allow the primer to dry according to the manufacturer’s instructions.
5. Once the primer has dried, use sandpaper to sand the surface of the print one final time, until it is smooth and free of imperfections. You can now apply a final finish such as paint or a clear coat to protect and enhance the appearance of the print.

5. Vapor Smoothing

Vapor smoothing involves exposing the print to the vapor of a solvent such as acetone or isopropyl alcohol, which melts and smooths the surface of the print.

This method can produce very smooth results, but requires a special vapor chamber or enclosure.

For smaller prints, you can use an airtight container or jar. 

1. Select a container that is larger enough to hold the print and place a support inside it. 
2. Soak paper towels in acetone or isopropyl alcohol and place them on the bottom and walls of the container. The wet paper should stick to the surface. 
3. Place your print on the support and close the container. Let the vapors work their magic for six to 12 hours, preferably overnight. Inspect the print and if you’re happy with the results, remove it from the container and wipe it with a damp cloth. 

When done correctly, vapor smoothing doesn’t require further post-processing.

This method works best for ABS and some specialty filaments such as ASA, HIPS, and PMMA.

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Impact Of Filament Type On Smoothing Techniques

Finding the best smoothing technique for your filament type goes beyond choosing a method from the list above.

You should choose based on the filament type – sanding is the only method that works with all filaments.

ABS

Acetone vapor smoothing is a highly effective method for smoothing ABS prints. This method can be used to melt and smooth the surface of the print, resulting in a glossy finish. 

Alternatively, heat can be used to melt and smooth the surface of ABS prints. Use a heat gun or other heat source to apply heat to the surface of the print, being careful not to overheat and deform the print.

ABS can also be smoothed using other chemicals, such as MEK (methyl ethyl ketone) or THF. These chemicals can be applied with a brush or soaked into a cloth and rubbed onto the surface of the print to melt and smooth the surface.

PETG

PETG is a popular material for 3D printing, and while it is generally more resistant to warping and shrinking than ABS, it can be more difficult to smooth due to its chemical resistance.

Sanding is a simple and effective way to smooth the surface of PETG prints. Use progressively finer grits of sandpaper to achieve a smoother finish.

PETG can also be smoothed using a flame polishing technique that involves briefly exposing the surface of the print to a flame. This method melts the surface of the PETG and creates a smooth, glossy finish.

However, it can be difficult to control the flame and avoid overheating or melting the print.

Chemicals such as dichloromethane or ethyl acetate can be used to smooth PETG prints. Use a vapor technique similar to the acetone vapor method used for ABS. However, the effectiveness of this method can vary depending on the brand of PETG.

PLA

PLA is a popular material for 3D printing due to its ease of use and low warping, but it can be difficult to smooth compared to other materials such as ABS or PETG. Similar to PETG, PLA is best smoothed through sanding.

You can also use chemicals such as THF or a heat gun. 

While acetone is not effective for smoothing PLA, it can be used to create a glossy finish on the surface of the print. Place the print in a sealed container with a small amount of acetone and allow the fumes to penetrate the print for several minutes.

Nylon

Nylon is a durable and strong material, but it can be challenging to smooth due to its high melting point and chemical resistance. 

Chemical smoothing with acetone or ethyl acetate is often the preferred smoothing method for this filament type. These chemicals can dissolve the surface of the nylon and result in a smoother finish. 

You can use a vapor technique or dab the print with a cloth soaked in solvent. It is important to note that this method might not work on all nylon filaments. The alternative is sanding.

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Best Practices For Smoothing 3D Prints

Smoothing 3D prints can be a laborious and frustrating process. These tips might help you achieve the desired result faster.

Don’t Skip Coarse Sandpaper 

Skipping steps and sanding with fine grit sandpaper alone might seem tempting, but you won’t save time. Fine-grit sandpaper is typically unable to remove larger imperfections, or you’ll have to put in extra effort.

If the part is large or intricate, consider using a sander.

Work in Small Sections 

The easiest way to get the job done is by working in small sections at a time. Make sure one section is properly sanded and smoothed before moving on to the next.

In the end, do a final pass with fine-grit sandpaper over the entire surface.

Sand Before Vapor Smoothing 

Vapor smoothing can effectively remove layer lines and other minor defects, but if you’re dealing with major issues, sanding the print before vapor smoothing can speed up the post-processing.

A quick pass with coarse or medium grit sandpaper should suffice in this case.

Test Beforehand

Sanding is the only smoothing technique that you can use without worrying too much. For all other methods, print a small part or use a piece of filament to see how the material reacts to the chemical that you want to use.

The same goes for heat smoothing – testing on a small part can help you set the right temperature for the task.

Consider a Finishing Coat 

No matter what smoothing method you used, consider applying a finishing coat to the part when you’re done.

Plastic spray paints come in a variety of colors, or you could use a clear product to enhance glossiness and make the print even smoother.

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Frequently Asked Questions

Why is my 3D print surface not smooth?

There are various reasons why your print is not smooth.

The most common reason is an incorrect layer height, but improper bed leveling, a too fast print speed, poor filament quality, or using wet filament can all impact the final result.

What filament is best for acetone smoothing?

Acetone smoothing works best on ABS filament.

You might also be able to use it on ASA, but for other filaments, you should consider alternative methods.

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Conclusion

From filament quality to printer calibration, there are a variety of factors that can affect the surface of the print. If the surface is not smooth, you can correct the problem by sanding the imperfections, treating the part with chemical vapors, or immersing the part in solvents.

Other methods involve using heat or fillers and primers. No matter which method you employ, applying a finishing coat can greatly improve part quality.