How to Smooth 3D Prints

3D printing is an incredible technology that allows for the creation of complex objects layer by layer. However, one common issue with 3D-printed parts, particularly those made using Fused Deposition Modeling (FDM), is the appearance of layer lines. These lines can detract from the aesthetic appeal and functionality of the printed object. Fortunately, there are several methods to smooth 3D prints, enhancing their appearance and making them feel more like traditionally manufactured products. This blog will cover various techniques for smoothing 3D prints made from different materials, including necessary safety precautions.

Understanding the Basics of Smoothing 3D Prints

Before diving into the methods, it’s essential to understand why smoothing is necessary and how different materials react to various smoothing techniques.

Layer Lines: 3D prints are made by depositing material layer by layer. The layer height (or resolution) of the print dictates how visible these lines will be. While a finer layer height reduces the visibility of these lines, they will still be present to some extent.

Material Properties: Different 3D printing materials have unique properties that affect how they can be smoothed. For instance, ABS (Acrylonitrile Butadiene Styrene) is more receptive to chemical smoothing than PLA (Polylactic Acid).

Smoothing Methods for Different Skill Levels

Beginners

For those just starting out with 3D printing and smoothing, these methods are generally easier to master:

• Sanding: A straightforward technique that requires minimal equipment and can be learned quickly.
• Filler priming: Relatively simple to apply and can hide minor imperfections.
• Heat smoothing (for ABS): While requiring some practice, a heat gun is readily available and the process is relatively intuitive.

Intermediate

As you gain more experience, you can tackle these methods:

• Chemical smoothing (ABS and resin): Requires careful handling of chemicals but can produce excellent results.
• Wet sanding: Offers a finer finish but requires more attention to detail.

Advanced

For those seeking professional-level results:

• Airbrushing: Mastering airbrushing takes practice and skill but can create stunning finishes.
• Multiple method combinations: Combining techniques like sanding, chemical smoothing, and airbrushing can achieve exceptional results.

Methods to Smooth 3D Prints

1. Sanding

Sanding is a straightforward and widely used method to smooth 3D prints. It involves using sandpaper to manually or mechanically smooth out the surface of the print. This method works well for both FDM and resin prints, though the process varies slightly depending on the material.

Steps for Sanding FDM Prints:

1. Start with a coarse grit (100-220): Begin by using coarse sandpaper (around 100-220 grit) to remove the most visible layer lines. This step is crucial for leveling the surface and preparing it for finer sanding.
2. Move to a medium grit (400-600): After the initial sanding, switch to a medium grit sandpaper (400-600). This step further smooths the surface and removes any scratches left by the coarse sandpaper.
3. Finish with a fine grit (800-2000): To achieve a polished finish, use fine grit sandpaper (800-2000). This step will give your print a smooth, almost glossy appearance.
4. Wet Sanding (Optional): For an even smoother finish, especially on PLA prints, you can use wet sanding. This involves dipping the fine grit sandpaper in water before sanding. Wet sanding reduces dust and helps achieve a more uniform finish.

Steps for Sanding Resin Prints:

1. Start with a fine grit (400-600): Resin prints are generally smoother than FDM prints, so you can start with a finer grit sandpaper (400-600) to smooth out the surface without damaging the details.
2. Use higher grits (800-2000): Continue with finer grits to achieve a polished finish. Resin prints can benefit greatly from wet sanding, especially if you're aiming for a transparent or semi-transparent finish.

Safety Precautions:

• Protective Gear:Always wear a dust mask or respirator when sanding, as fine particles can be harmful if inhaled. Protective eyewear is also recommended to prevent dust from getting into your eyes.
• Ventilation:Sand in a well-ventilated area or use a vacuum system to capture dust particles.

2. Chemical Smoothing

Chemical smoothing involves using solvents or other chemicals to dissolve the surface layer of the print, effectively eliminating layer lines and creating a smooth finish. This method is particularly effective for certain materials like ABS and resin. However, working with chemicals requires strict adherence to safety precautions to avoid health hazards.

Chemical Smoothing for ABS Prints:

• Acetone Vapor Smoothing: ABS is highly receptive to acetone vapor. The print is placed in a sealed chamber with a small amount of acetone, which vaporizes and condenses on the surface of the print, smoothing out layer lines.
• Method: Place a small amount of acetone in a metal container and suspend the ABS print above the liquid. Seal the container and let the acetone vapor work for 10-15 minutes. Remove the print and allow it to air dry.

Chemical Smoothing for PLA Prints:

• Tetrahydrofuran (THF) or Ethyl Acetate: PLA is less receptive to common solvents like acetone. However, it can be smoothed using THF or ethyl acetate. These chemicals are more aggressive, so care must be taken to avoid over-exposure, which could damage the print.
• Method: Apply a small amount of THF or ethyl acetate to the surface of the print using a brush, or suspend the print in a vapor chamber as with ABS.

Chemical Smoothing for Resin Prints:

• Isopropyl Alcohol (IPA): For resin prints, isopropyl alcohol (99%) is often used during the post-processing stage. While it doesn’t smooth the print, it cleans off uncured resin, which can contribute to a smoother finish.
• Method:Submerge the resin print in an IPA bath and gently agitate it to remove uncured resin. Follow with UV curing to harden the surface.

Chemical Safety Precautions:

Acetone (ABS Smoothing):

• Protective Gear: Wear nitrile gloves, safety goggles, and a respirator with organic vapor cartridges.
• Ventilation:Perform the process in a well-ventilated area or under a fume hood. Acetone fumes are highly flammable and toxic if inhaled.
• Fire Safety: Keep acetone away from open flames, sparks, and heat sources. Store it in a cool, dry place in a tightly sealed container.

Tetrahydrofuran (THF) and Ethyl Acetate (PLA Smoothing):

• Protective Gear: Wear chemical-resistant gloves, safety goggles, and a respirator with organic vapor cartridges.
• Ventilation: Use THF and ethyl acetate in a well-ventilated area or under a fume hood. Both chemicals can cause respiratory irritation and are flammable.
• Handling: Avoid skin contact, as these chemicals can cause irritation or burns. Use only the amount needed for the task and store the rest securely.

Isopropyl Alcohol (Resin Smoothing):

• Protective Gear: Wear gloves, safety goggles, and a mask. While IPA is less aggressive, it can still cause skin irritation and is flammable.
• Ventilation: Use IPA in a well-ventilated area, especially when working with large volumes. Ensure proper storage away from heat sources and open flames.
• Handling: Avoid prolonged skin contact, and do not ingest. Use in moderation to prevent excessive exposure.

3. Heat Smoothing

Heat smoothing involves using controlled heat to soften the surface of a print, allowing the layer lines to meld together. This method works well for thermoplastic materials like ABS and PETG but is not recommended for PLA, which has a lower melting point.

Heat Smoothing for ABS Prints:

• Heat Gun: A heat gun can be used to smooth ABS prints. The heat is applied evenly across the surface of the print, softening the plastic and reducing the appearance of layer lines.
• Method: Hold the heat gun a few inches away from the print and move it back and forth to avoid overheating any single spot. This method requires a steady hand and careful control of the heat.

Heat Smoothing for PETG Prints:

• Heat Gun: Similar to ABS, PETG can also be smoothed using a heat gun. However, PETG is more sensitive to heat and can easily deform, so it’s essential to use a lower heat setting and keep the heat gun moving.

Safety Precautions:

• Protective Gear: Wear heat-resistant gloves to protect your hands from burns. Safety goggles are also recommended to shield your eyes from debris or accidental contact with the hot nozzle.
• Fire Safety: Be cautious of flammable materials in the workspace, and avoid pointing the heat gun at anything other than the print.

4. Filler Priming

Filler priming involves applying a filler primer spray to the surface of the print, filling in the gaps and layer lines. This method is often used in conjunction with sanding to achieve a smooth finish.

Filler Priming for FDM Prints:

• Application: After the initial sanding, spray the print with a filler primer, which will fill in the small gaps and imperfections. Once dry, sand the print again with fine grit sandpaper to achieve a smooth surface.
• Painting: Filler priming is an excellent preparation step if you plan to paint your print. The smooth, even surface it creates ensures that paint adheres well and looks uniform.

Safety Precautions:

• Protective Gear: Wear a respirator or mask to avoid inhaling fumes from the primer. Safety goggles and gloves are also recommended.
• Ventilation: Spray in a well-ventilated area or a spray booth to minimize exposure to fumes.

Filament Types and Post-Processing

Understanding how different filament types react to post-processing is crucial for achieving optimal results. Here's a breakdown of some common filaments and their characteristics:

PLA (Polylactic Acid)

• Smoothing: Responds well to sanding and filler priming. Less receptive to chemical smoothing. Heat smoothing is not recommended due to its low melting point.
• Painting: Adheres well to paint after proper preparation.
• Other considerations: Biodegradable, good for beginners, but prone to warping.

ABS (Acrylonitrile Butadiene Styrene)

• Smoothing: Highly responsive to chemical smoothing (acetone vapor), sanding, and heat smoothing.
• Painting: Adheres well to paint after proper preparation.
• Other considerations: Stronger and more durable than PLA, but requires higher temperatures for printing and has a tendency to warp.

PETG (Polyethylene Terephthalate Glycol)

• Smoothing: Can be sanded and heat smoothed with care. Responds to some chemical smoothing methods.
• Painting: Adheres well to paint after proper preparation.
• Other considerations: Tough, flexible, and has good print quality, but can be prone to stringing.

TPU (Thermoplastic Polyurethane)

• Smoothing: Difficult to smooth due to its flexible nature. Sanding can be challenging and may damage the material.
• Painting: Adhesion can be problematic due to the material's oily surface. Special primers might be necessary.
• Other considerations: Flexible and elastic, often used for creating rubber-like parts.

Nylon

• Smoothing: Can be sanded and heat smoothed with care. Some types of nylon respond to chemical smoothing.
• Painting: Adhesion can be challenging due to its smooth surface. Proper preparation is essential.
• Other considerations: Strong, durable, and resistant to chemicals and abrasion.

Other Filaments

• HIPS: Similar to ABS in terms of post-processing. Often used as support material for ABS prints.
• TPU/PLA blends: Properties can vary depending on the ratio of TPU to PLA. Generally, more difficult to smooth than pure PLA.
• Metal-filled filaments: Post-processing can be challenging due to the metal particles. Sanding and painting might require special considerations.
• Wood-filled filaments: Sanding and finishing can be similar to wood, but the plastic matrix can affect the results.

Painting and Sealing Sanded 3D Prints

Once you've smoothed your 3D print, painting and sealing it can further enhance its appearance and durability. The process of painting and sealing differs slightly between FDM and resin prints.

Painting FDM Prints

After smoothing an FDM print, you can apply paint to achieve the desired color and finish.

Steps for Painting FDM Prints:

1. Prime the Surface: Start by applying a primer coat to the sanded surface. This helps the paint adhere better and creates a uniform base color. Use a spray primer for even coverage.
2. Apply Paint: Once the primer is dry, apply the paint in thin, even coats. Acrylic paints are commonly used for 3D prints because they dry quickly and offer a wide range of colors.
3. Allow Drying Time: Let each coat of paint dry completely before applying the next. This prevents smudging and ensures a smooth finish.
4. Seal the Paint: After the final coat of paint has dried, apply a clear sealant to protect the paint and give it a glossy or matte finish, depending on your preference.

Safety Precautions:

• Protective Gear: Wear gloves and a mask when painting, especially when using spray paints. Safety goggles are recommended to protect your eyes.
• Ventilation: Paint in a well-ventilated area or a spray booth to avoid inhaling fumes.

Painting Resin Prints

Resin prints typically have a smoother surface right out of the printer, making them ideal for painting without extensive sanding.

Steps for Painting Resin Prints:

1. Clean the Surface: Before painting, clean the resin print with isopropyl alcohol to remove any remaining uncured resin or dust.
2. Apply Primer: Just like with FDM prints, start with a primer to help the paint adhere. Resin prints often need a primer designed for plastic surfaces.
3. Apply Paint: Use thin coats of paint, allowing each layer to dry before adding the next. Because resin prints have finer details, it's important to apply the paint carefully to avoid obscuring them.
4. Seal the Paint: Once the paint has dried, apply a clear coat to protect the finish and add durability to the print.

Safety Precautions:

• Protective Gear: Use gloves, safety goggles, and a mask when handling paints and primers. Resin prints should be handled with care, as uncured resin can cause skin irritation.
• Ventilation: Ensure good ventilation when painting resin prints, as fumes from the paints and primers can be harmful if inhaled.

Types of Paint for 3D Prints

Different types of paint can be used on 3D prints, each offering unique benefits. The choice of paint depends on the material of the print and the desired finish.

Acrylic Paint

Acrylic paint is one of the most popular choices for painting 3D prints. It’s water-based, easy to use, and available in a wide range of colors.

• Pros: Quick drying, easy cleanup, versatile.
• Cons: May require multiple coats for full coverage, not as durable as some other types.

Steps for Acrylic Painting:

1. Prime the Surface: Apply a primer to ensure the acrylic paint adheres well to the print.
2. Apply Paint: Use thin coats, allowing each to dry before applying the next.
3. Seal the Paint: Apply a clear acrylic sealant for durability.

Enamel Paint

Enamel paint is oil-based and provides a durable, glossy finish. It’s often used for models and miniatures.

• Pros: Durable, glossy finish, good for detailed work.
• Cons: Longer drying time, requires solvents for cleanup.

Steps for Enamel Painting:

1. Prime the Surface: Use a primer that is compatible with enamel paint.
2. Apply Paint: Apply in thin layers, being careful not to obscure details.
3. Seal the Paint: Use an enamel clear coat to protect the finish.

Spray Paint

Spray paint is a quick and efficient way to paint large areas of a 3D print. It provides even coverage and is available in a variety of finishes.

• Pros: Fast application, even coverage, available in many colors and finishes.
• Cons: Requires a well-ventilated area, overspray can be messy.

Steps for Spray Painting:

1. Prime the Surface: Use a spray primer for even coverage.
2. Apply Paint: Hold the can 6-12 inches from the print and apply in light, even coats.
3. Seal the Paint: Apply a clear spray sealant to protect the finish.

Safety Precautions for Painting:

• Acrylic and Enamel Painting: Use a respirator or mask, especially with enamel paints, which can release harmful fumes. Work in a well-ventilated area or use a spray booth.
• Spray Painting: Always wear a mask, gloves, and safety goggles. Spray in a well-ventilated area or outdoors to minimize inhalation of fumes.

Brush Painting vs. Airbrushing

Both brush painting and airbrushing have their place in finishing 3D prints, each offering unique advantages depending on the desired outcome.

Brush Painting

Brush painting is ideal for detailed work and small areas. It allows for precise control, making it perfect for adding highlights, shadows, and intricate designs.

• Pros: Precise control, no need for special equipment, good for detailed work.
• Cons: Can leave brush marks, slower process, requires multiple coats for even coverage.

Steps for Brush Painting:

1. Prepare the Surface: Prime the print and ensure it’s smooth and clean.
2. Apply Paint: Use small, even strokes, and build up layers gradually.
3. Seal the Paint: Once the painting is complete, apply a clear sealant.

Airbrushing

Airbrushing offers a smooth, even finish and is ideal for covering large areas quickly. It’s perfect for achieving gradients and detailed shading.

• Pros: Smooth, even finish, quick coverage, excellent for gradients and shading.
• Cons: Requires special equipment, needs practice for best results, more setup and cleanup time.

Steps for Airbrushing:

1. Prepare the Surface: Prime the print and ensure it’s smooth and clean.
2. Set Up the Airbrush: Mix the paint to the right consistency, and set the airbrush to the desired pressure.
3. Apply Paint: Use smooth, even passes to build up the color. Start with light coats and gradually build up to the desired opacity.
4. Seal the Paint: Apply a clear coat to protect the finish and add durability.

Safety Precautions:

• Brush Painting: Use a mask if working with paints that release fumes, and ensure proper ventilation.
• Airbrushing: Always use a respirator, as the fine mist from airbrushing can be easily inhaled. Work in a well-ventilated area or use an airbrush booth with proper exhaust.

Environmental Impact and Chemical Handling

While smoothing 3D prints can significantly enhance their appearance, it's crucial to be mindful of the environmental impact and safety considerations associated with certain methods.

Environmental Impact

• Chemical Usage: Many smoothing techniques involve the use of chemicals, such as acetone, THF, and ethyl acetate. These chemicals can be harmful to the environment if not disposed of properly.
• Waste Generation: Sanding and other abrasive methods produce dust and waste materials that can contribute to pollution.
• Energy Consumption: Some methods, like heat smoothing, require energy input, which can indirectly impact the environment.

Chemical Handling and Disposal

Proper handling and disposal of chemicals are essential to protect human health and the environment.

• Safety Equipment: Always wear appropriate protective gear, including gloves, safety goggles, and a respirator, when handling chemicals.
• Ventilation: Ensure adequate ventilation when working with chemicals to prevent inhalation of fumes.
• Storage: Store chemicals in properly labeled, airtight containers away from heat sources and incompatible substances.
• Disposal: Dispose of chemicals according to local regulations. Never pour chemicals down the drain or into the environment. Contact your local waste management authority for proper disposal guidelines.

Reducing Environmental Impact

• Choose Environmentally Friendly Alternatives: Consider using water-based or biodegradable cleaning agents whenever possible.
• Recycling: Recycle sanding dust and other waste materials whenever feasible.
• Energy Efficiency: Optimize your smoothing process to minimize energy consumption.
• Local Regulations: Stay informed about local environmental regulations and guidelines.

FAQs

• Do 3D prints come out smooth?
  • While some 3D printing technologies like SLA and DLP naturally produce incredibly smooth prints, others like FDM often result in visible layer lines and rougher surfaces. Post-processing techniques like sanding or vapor smoothing can enhance the smoothness of 3D printed parts when needed.
• What is the best chemical to smooth PLA?
  • Tetrahydrofuran (THF) or Ethyl Acetate:These chemicals can smooth PLA, but should be used with caution due to their aggressive nature.
• What is the smoothest type of 3D printing?
  • Stereolithography (SLA) 3D printing offers the smoothest surface finish. This technology cures liquid resin layer-by-layer using a precision laser, resulting in stunningly smooth and detailed prints with a glossy appearance straight from the printer, often rivaling injection-molded plastics.
• How to get a smooth 3D print?
  • Optimize Settings: Use a lower layer height and adjust print speed for finer details.
  • Temperature Control: Ensure the correct nozzle temperature for your filament to avoid rough surfaces.
  • Proper Adhesion: Use a clean, leveled bed with adhesive aids like glue or tape.
  • Post-Processing: Sand the print lightly and use a filler primer for a smoother finish. For ABS, consider acetone vapor smoothing.