3D Print Finishing: Guide For Finishing 3D Printed Parts

3D print finishing is a useful skill whether you’re manufacturing 3D printed parts or just 3D printing them yourself. This page describes the various 3D print finishing processes for FDM and PolyJet 3D printed parts, along with tricks and advice for improving the appearance and feel of your prototypes.

As a case study, let’s begin with a straightforward Watch stand design. This stand needs to be completed to a standard that matches the sleek exterior of an Apple Watch because it has pockets and other internal and external features. Typically, components require additional labor to get the required surface roughness, and mastering this technique is a crucial ability that can ultimately reduce post-processing costs.

The sort of material your 3D printed parts is constructed of will eventually determine how your 3D printing post processing goes. Three base materials will be compared for the purposes of this analysis:

PLA: Although the pricing is lower and the results aren’t as polished, PLA is the best material option for those on a restricted budget.

ABS: ABS is a fantastic option for finances that are reasonable. Although it is more dependable than PLA, it is not as economical as PLA.

VeroBlack or VeroWhite: These two materials produce pieces of the greatest caliber, with the smoothest finishes and the most precise dimensions.

Post-Processing Overview

To achieve the best possible each unique 3D print finishing, we must address specific challenges and considerations. The post-processing of our watch stand involves a blend of repair and preparation before sanding and painting. The end result should be a smooth, matte black surface for all three materials used. Detailed print settings for each material are presented below, with a summary of results provided in the article’s conclusion.

ABS Printing (on a Dimension Elite)

The Dimension Elite produces prints that are smooth and clean, ready for sanding after a post-printing NaOH bath. However, visible stepping lines between printed object layers must be addressed to prevent them from showing up in the final paint coat.

Fortunately, ABS’s high melting point and sandability make it easy to remove these lines.

Materials for ABS 3D Printed Part Finishing

To conduct 3D print finishing, you’ll need:

• Sandpaper (grits 100 to 600)
• Medium, fine, and extra-fine sanding sponges
• XTC-3D brush-on coating (Alternatively, Bondo putty can be used for hole filling)
• Razor blade
• Foam brush, mixing cups, and popsicle sticks
• Sandable Krylon Primer
• Montana Acrylic Primer in Shock Black
• Matte Acrylic Varnish

Sanding the ABS 3D Printed Part

Sanding an ABS print is a straightforward process. Start with 100-200 grit sandpaper to eliminate stepping lines, gradually progressing to 600 fine grit sandpaper for a smooth finish. Sand in small circular movements evenly across the part’s surface, avoiding sanding in a single direction, particularly in the direction of stepping lines to prevent striations or “trenches” in the print.

Be cautious as ABS material is removed quickly during sanding. Over-sanding can compromise critical dimensions, so avoid overdoing it. As little as .010″ of material removal can eliminate stepping layers.

After sanding, you may encounter holes caused by incomplete layers. These holes can perforate through the paint coat, creating sinkholes.

Repairing the Incomplete Layer

Use a thin, sandable epoxy, such as XTC-3D, to fill in the gaps. XTC-3D is cost-effective, quick, and performs well. Follow the manufacturer’s recommended pot life and maintain a weight ratio of 100 Part A to 42 Part B. Ensure your part is clean and free of oils and sanding dust before applying XTC-3D.

Fill the holes or gaps with a thin coat, and use a razor blade to remove excess material, avoiding areas you don’t want to fill, like letters. Allow XTC-3D to dry as per the manufacturer’s instructions, and then sand away excess material with 300 to 600 fine grit sandpaper for a uniform surface.

Preparing and Painting the ABS 3D Printed Part

You can paint 3D printed parts using various materials, such as acrylics, enamels, sprays, and airbrushes. In this example, Montana spray can paints are used, following a simple process: prime, dry, paint, dry, varnish, dry. Ensure a dust-free, oil-free, and hole-free surface. Shake paint cans for at least two minutes before painting and maintain a clean spray cap.

Apply paint in light coats, particularly for parts with internal or obscured geometries. Work in well-ventilated, well-lit areas.

The Final Result for ABS 3D Printed Part

The finished ABS part is matte black and smooth to the touch, with minimal evidence of layering on most surfaces. Some key points to note include the challenges of sanding sharp internal pockets and the need to sacrifice some dimensional accuracy due to extensive surface material removal during the sanding process. Filling incomplete layers with a thin coat of XTC-3D effectively eliminates holes in the final paint layer.

VeroBlack (Printed on an Objet30)

The Objet30 printer, with its remarkable .0011” resolution, exhibits some minimal stepping between layers, which is far less conspicuous compared to our FDM print. Nevertheless, upon emerging from the printer, Objet30 prints are accompanied by a substantial layer of support structure material. Our initial step in the 3D print finishing process involves the removal of this support structure and the remnants it leaves behind.

Materials Required for VeroBlack 3D Printed Part Finishing

You will need the following materials for refining VeroBlack printed parts:

• Sandpaper (ranging from 100 to 600 grit)
• Medium, fine, and extra-fine sanding sponges
• Sandable Krylon Primer
• Montana Acrylic Primer in Shock Black
• Matte Acrylic Varnish

Sanding the VeroBlack 3D Printed Part

Once the support structure is eliminated, commence the wet sanding process using 100 grit sandpaper to remove the residual material. Gradually progress to 300 grit sandpaper, which will result in the residue coming off in small, soft, white fragments. This stage constitutes the most labor-intensive part of the VeroBlack 3D print finishing procedure, typically taking around 40 minutes to remove the residual layer. If you run your fingernail across the part before sanding, you’ll notice it has a harder, more plastic-like texture beneath the gummy residue.

As the residual layer is eliminated, the part’s surface will start to feel smooth. Continue wet sanding with 600 fine grit sandpaper until the entire part achieves a uniform smoothness.

Pro Tip: Wet sanding is highly effective as water aids in breaking up the residue, resulting in a smooth, residue-free, paintable, and consistent surface.

After sanding, thoroughly clean the part using soap and water to eliminate any residual material. It is advisable to use compressed air for drying to ensure that no dust accumulates.

It’s important to note that VeroBlack behaves similarly to ABS. Once you breach the residual layer, removing the actual VeroBlack material is relatively simple. Therefore, exercise caution to avoid over-sanding and compromising critical dimensions. Removing as little as .005” is typically sufficient to completely eliminate any visible stepping layers.

Priming and Painting the VeroBlack 3D Printed Part

The VeroBlack part can be painted following the same process as the ABS part. Montana spray paint is used, and the procedure involves priming, drying, painting, drying, and varnishing.

Once again, adhere to these standard spray-painting principles:

• Ensure the surface is free from oil, dust, and imperfections.
• Shake each paint can for at least two minutes before application.
• Ensure the spray cap is clean to prevent drips.
• Monitor the paint application to prevent pooling and dripping.
• Apply multiple light coats rather than a few heavy coats, especially for 3D printed parts with intricate internal geometries.
• Perform the painting in controlled, well-ventilated, and well-lit areas.

Final Results for the VeroBlack 3D Printed Part

Our completed VeroBlack part boasts a matte black finish and a smooth texture. Nevertheless, some of the internal corners were not sufficiently sanded to remove the residue, leading to visible paint peeling in those areas (refer to item 1 in the image above). This may potentially worsen over time. Additionally, some minor stepping is evident on the part (refer to item 2 above), which could have been eliminated with an additional 30 minutes of thorough sanding.

PLA (Printed on a 5th gen. Replicator)

Lastly, we have a PLA print, known for its challenging 3D print finishing process. However, with some clever techniques and patience, we can achieve the same matte finish excellence as the ABS and VeroBlack prints.

Our Replicator-printed PLA part exhibited pronounced striations upon removal from the build plate, as seen in the parallel grooves within the part’s layers. These grooves could be attributed to the printer’s quality, but we can effectively mitigate them.

Sanding the PLA 3D Printed Part

Sanding PLA can be a tricky task due to its soft and gummy nature when sanded too aggressively. To smooth it with minimal effort and abrasion, consider the following approach.

If you opt to sand PLA directly, the process is relatively straightforward. Initiate with a coarser (100-200) grit sandpaper, targeting the bumpy striations and any remaining raft or support materials. Especially in the case of MakerBot supports, use a flush cutter or pliers to remove them, and then use a rotary multi-tool to eliminate any remnants before sanding.

Depending on the size and geometry of your part, you may find yourself working in the 100-300 grit sandpaper range to smooth out striations and remnants of support structures.

Once the layering and striations become less prominent, transition to finer grits (400-600) sandpaper to achieve a glossy surface ready for priming and painting.

Pro Tip: Exercise patience during the 3D print finishing process, especially when sanding PLA. Sand in small, even circular motions across the part’s surface. If using a sanding multi-tool on PLA, be cautious not to overheat or melt your 3D printed part.

Please note that PLA is not as amenable to smoothing with acetone as ABS, and removing stepping between layers, particularly in prints with severe striations like ours, will require more effort.

An alternative method to direct sanding of PLA prints is to apply a layer of XTC-3D to smooth the print before sanding.

Finishing PLA 3D Printed Parts

Before applying XTC-3D, ensure that your part is thoroughly clean, free from oils, and devoid of sanding dust, following the established pattern. Wash the part with soap, dry it with compressed air to eliminate dust, and don protective gloves.

Apply the first coat of XTC-3D as a thin (1/64”) layer, allowing it to self-level. Depending on the size of your part, you may need to apply the XTC-3D in sections, but keep overlapping to a minimum. Allow 90 minutes between the first and second coats, and after the final coat, wait for 2 hours until the glossy surface becomes tack-free.

Given the severity of striations, multiple coats will be necessary to achieve a uniformly smooth surface, so exercising patience is crucial. Thinner, glossy finish coats tend to level more effectively than thicker ones.

Pro Tip: Be watchful for pooling in internal pockets, and remove any pooling that occurs before the XTC-3D begins to dry.

It’s worth noting that XTC-3D may affect critical dimensions, but applying thin coats will minimize this impact.

Once the XTC-3D layer has solidified after the final coat, you’re ready for sanding. Begin with 300 grit sandpaper, using small circular movements to level the surface. If there are stubborn waviness patterns, consider using a coarser grit sandpaper. Progress to 600 grit sandpaper to achieve a smooth, level surface.

Following sanding, thoroughly clean your part with soap and water, and use compressed air to ensure it is entirely free of dust before painting.

Painting the PLA 3D Printed Part

Painting PLA follows the same process as ABS and VeroBlack parts: prime, dry, paint, dry, varnish, dry.

Adhere to these standard spray-painting principles:

• Ensure the surface is devoid of oil, dust, and imperfections.
• Shake each paint can for at least two minutes before application.
• Ensure the spray cap is clean to prevent drips.
• Monitor the paint application to prevent pooling and dripping.
• Apply multiple light coats rather than a few heavy ones, particularly for 3D printed parts with intricate internal geometries.
• Paint only in controlled, well-ventilated, and well-lit areas.

Final Results for the PLA 3D Printed Part

The XTC-3D coated PLA part is matte black and smooth to the touch, yet some challenges persist. The XTC-3D has been effective in smoothing the part and facilitating sanding, but it has pooled in internal pockets, visible through the paint finish. Additionally, striations remain evident on the part. An additional 30 minutes of thorough sanding could have prevented these striations from showing through the final paint finish.

Results and Closing Thoughts

Upon achieving a smooth, matte black finish for all three parts, let’s explore the distinctions in the processes, time, materials, and final outcomes.

Divergence in 3D Print Finishing Processes

ABS (Dimension Elite):

• Sand with grits ranging from 100 to 600.
• Repair any holes with XTC-3D (may not be necessary for all parts).
• Sand away XTC-3D using 300 to 600 grit sandpaper.
• Prime, Paint, Varnish.

VeroBlack (Objet30):

• Sand with grits ranging from 100 to 600.
• Prime, Paint, Varnish.

PLA (Replicator 5th gen.):

• Coat in 1 to 3 layers of XTC-3D (depending on the severity of striations on your print).
• Sand away XTC-3D with grits from 100 to 600.
• Prime, Paint, Varnish.

Variations in Time

The PLA part required the most time to finish due to the XTC-3D coating application. Even without XTC-3D, PLA generally demands more time for sanding compared to ABS or VeroBlack. In our case, the VeroBlack was the quickest to finish, particularly as we employed XTC-3D to repair our ABS print, making stepping between layers less pronounced.

Generally, VeroBlack offers the fastest route to achieving a smooth, matte black finish.

Pro Tip: For expedited transitions from 3D printing to a photoshoot, opt for the Dimension Elite or Objet30 printers, as their support material can be rapidly dissolved, unlike the PLA supports on a Replicator print, which require more time for removal.

Variations in Cost and Materials

PLA is the most cost-effective of the three, at $20 per part, followed by ABS at $55, and VeroBlack at $110. However, these costs do not encompass the value of the time and effort required to attain a finished part. VeroBlack emerges as the best value for your investment, thanks to its ease of 3D print finishing and ability to produce highly accurate models.

The Final Outcomes

At first glance, all three Apple Watch stands may seem similar, but there are distinct differences in their final finishes.

Both the ABS and PLA finished prints exhibit noticeable stepping between layers, evident in the final product. VeroBlack requires considerably less effort to rectify these steps, and they are less apparent in the final paint coat.

While the ABS and VeroBlack finished prints share similar surface finishes, the ABS required the removal of more material (approximately .020”) during the sanding process to eliminate stepping between layers. In contrast, VeroBlack necessitated less sanding, resulting in final dimensions closer to the original design intent.

In summary, here are the key insights into each print:

VeroBlack: High layer resolution (.0011”) minimizes the need for extensive sanding to achieve a smooth, paintable part. Critical dimensions remain intact, and no repairs are necessary for finely detailed features.

ABS: While ABS parts are easy to sand, small, finely detailed features may require repairs and precise sanding to eliminate stepping between layers. Once these steps are resolved, painting is straightforward.

PLA: PLA is the most budget-friendly option but can also be the most challenging to finish, contingent on the support structures and print quality. It may require substantial sanding and repair through XTC-3D or Bondo filler.

Key Takeaways for Finishing 3D Printed Parts

• 3D print finishing entails a combination of processes, including smoothing application, sanding, polishing, cleaning, and painting, with the process varying according to the material used.
• Achieving a smooth finish with 3D printing is feasible, and post-processing significantly enhances part smoothness.
• Epoxy resins are a suitable choice for sealing PLA printed parts.
• Acetone smoothing is not recommended for PLA prints.
• In general, IPA or rubbing alcohol does not dissolve PLA, but some PLA varieties may be IPA soluble. Refer to your filament material datasheet or technical datasheet for clarification.
• PLA can be smoothed without sanding by applying a coating via dipping or spraying.
• ABS is tougher and lighter than PLA, while PLA is stronger and stiffer. Each has its ideal applications, with PLA often considered a hobbyist material and ABS preferred for prototyping.

3D Printing Finishing Services

We can meet all of your needs for 3D print finishing and 3D printing services. We specialize in creating unique 3D printed parts from a range of materials, and we streamline the process by using intelligent and automated workflows. Prototyping, injection molding, and CNC machining are other aspects of our optimized manufacturing services.
Please take a look at our website or the resources below for further details.

Related Resources:

Rapid Prototyping: To Projects From Prototype To Production

3D Printing VS. Injection Molding: Cost Analysis

5 Major Steps of Plastic Product Development and Production