Sofia Martinez
Polylactic acid (PLA) is a popular material for 3D printing due to its eco-friendly nature and ease of processing. However, achieving a smooth finish on 3D-printed PLA objects can be challenging. While sanding is a common technique to smooth 3D prints, it can be time-consuming and cause colour loss. To avoid this, some people use card or cabinet scrapers, which can quickly remove a lot of material without changing the object's dimensions. Others use chemical solvents such as Dichloromethane (DCM) or acetone to dissolve or soften the PLA, creating a seamless finish. Additionally, spot putty can be used to fill in low spots and layer lines, creating a smoother surface for painting.
| Characteristics | Values |
|---|---|
| PLA plastic composition | Polylactic acid (PLA) is made from renewable resources such as corn starch. |
| PLA plastic advantages | PLA is more eco-friendly than traditional plastics, requiring less energy to process. |
| Filing/Sanding PLA | It is possible to file or sand PLA to smoothen and finish 3D prints. However, some users have reported challenges in achieving desired results. |
| Sanding process | Start with 120-grit sandpaper, then move to higher grits, priming, sanding, spot putty, and repeat sanding. |
| Colour loss during sanding | PLA tends to lose its colour after sanding. Using a heat gun can help restore the original colour. |
| Alternative methods | Other methods to smooth PLA include using solvents like acetone, Dichloromethane (DCM), or THF (Tetrahydrofuran). |
| Scraping | Card/cabinet scrapers can be used to quickly remove material from 3D prints, creating a smooth surface without changing dimensions. |
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What You'll Learn
Sanding PLA prints
Prepare the Surface:
Before you begin sanding, it is essential to ensure that your PLA print is ready for the process. Use a cabinet scraper or a card scraper to remove any excess material and create a smooth base. These tools are effective in quickly removing a lot of material without altering the dimensions of your print. You can also use a coarse file to shape the PLA plastic and remove any rough edges. Hold the file firmly and tilt it away from your body in an upward position. Press the rough edge of the file along the top edge of the PLA, moving in an upward and outward manner. Repeat this process until you achieve a smooth surface.
Sanding Technique:
When you are ready to begin sanding, start with 120-grit sandpaper. This initial sanding step will help bring down the surface texture and create an even base for further refinishing. Always sand in the direction of the layers to avoid creating scratches that go against the grain. You can then apply a filler primer to fill in any remaining low spots or minor blemishes.
Spot Putty Application:
After sanding with 120-grit sandpaper, it's time to apply spot putty. Spot putty is a great material to fill in any remaining gaps or layer lines. Always wear gloves when working with spot putty, as it contains toxic substances. Using a pea-sized amount, smear the putty across the surface of your print, ensuring it fills in the gaps without losing the finer details. Allow the putty to cure for about 15 minutes, and then proceed to sanding again.
Refining the Finish:
Once the spot putty has cured, you can begin refining the finish. Start sanding again with 120-grit sandpaper, and then move up to 220-grit sandpaper. This gradual progression to finer sandpaper will help you achieve a smoother surface. You can repeat the process of applying spot putty and sanding as many times as needed to eliminate layering and create a seamless finish.
Painting and Polishing:
After you are satisfied with the smoothness of your PLA print, it's time to add the final touches. Apply a coat of primer and then your chosen paint, either matte or gloss, to give your print a polished look. Remember to spray in a back-and-forth motion, overlapping each pass to avoid noticeable drips. Additionally, if you wish to restore the colour that may have been lost during sanding, you can use a heat gun to quickly go over the surface. Ensure you don't get too close to the surface and use quick passes to avoid deforming your print.
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Using card/cabinet scrapers
Card/cabinet scrapers are an effective alternative to sanding 3D prints and can significantly reduce the time spent prepping PLA plastic for paint. They are thin pieces of sprung or stainless steel with a sharp burr on one or more edges.
To use a card/cabinet scraper, start by placing the scraper flat on a workbench. Then, using a burnisher, work the face of the scraper a dozen times or so to consolidate the edge. Next, clasp the scraper with a rag and get ready to roll the burr. Draw the burnisher over the edge, creating a slight burr. It is important to note that a smaller burr is preferable. This process should be repeated on all four edges of the scraper.
When using the scraper on PLA plastic, it is essential to provide support where the scraper meets the plastic to minimize bowing. Additionally, applying more pressure or using a thicker scraper can help achieve a more square finish.
Card/cabinet scrapers come in various shapes, including oval, pear-shaped, and curved edges. Curved edges, in particular, can make it easier to target small rough spots without affecting the surrounding areas. They are also more comfortable on the hands and help avoid rounding corners when working on edges.
Card/cabinet scrapers are a simple yet effective tool for refining 3D prints and can save significant time and effort compared to traditional sanding methods.
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Applying spot putty
When it comes to applying spot putty, there are several tools you can use. These include your gloved finger, a small paddle, scrapers, the side of a plastic scrap, or even a popsicle stick. The choice of tool depends on your personal preference and the area you are working on. For instance, a small spreader is ideal for tight spaces.
Before applying the spot putty, it is recommended to sand the surface with 120-grit sandpaper to reduce the surface texture. This step ensures that you create a smooth base for the putty to adhere to.
Now, take a pea-sized amount of putty and smear it across the surface of your PLA print. Spread the putty evenly, filling in gaps and blemishes, while also ensuring that it is not too thick, so you don't lose the finer details of your print. Don't worry about overdoing it, as spot putty is easy to sand off.
Once you've covered the entire print, wait for about 15 minutes for the putty to cure and become non-gummy. After curing, you can start sanding again with 120-grit sandpaper. This initial sanding after curing will be brief, as you are essentially wiping off the excess putty. You'll know you're ready for the next step when you see a light coating of putty with pink spots remaining on the surface. At this point, you can switch to 220-grit sandpaper for a finer finish.
It is important to note that spot putty contains dye, resin, and talcum powder, and its vapours are listed as harmful. Therefore, it is recommended to wear gloves and, if preferred, a mask to protect yourself during the application and sanding process.
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Dissolving PLA
Polylactic Acid (PLA) is a popular plastic for 3D printing due to its affordability, ease of use, and availability in many colours and varieties. It is also biodegradable, taking around 80 years to biodegrade, compared to a few hundred years for most other plastics.
There are several methods to dissolve PLA, some more effective than others. One common method is to use acetone, a solvent found in household products like nail polish remover and paint remover. However, acetone tends to make PLA rubbery and sticky rather than fully dissolving it, and it can ruin the strength and surface finish of a print. It is also highly flammable and toxic to humans.
Another option is to use ethyl acetate, which is highly effective at breaking down and dissolving PLA. It is also considered less toxic than other solvents, but it is still flammable, so proper protection and ventilation are necessary.
Other chemical solvents that can be used to dissolve PLA include:
- Tetrahydrofuran (THF): an industrial-grade solvent with a strong odour, readily available for dissolving PLA. It can be used in a vapour chamber or applied directly to the PLA surface, but it may not be 100% effective.
- Dichloroethane: effective for processing models of PLA.
- Weld-On #4 and #5: these products are considered rather dangerous, but they can dissolve PLA.
- DCM: capable of dissolving PLA, but not recommended due to associated health risks.
In addition to chemical methods, there are also manual techniques to smooth PLA prints, such as sanding and polishing. When choosing a method, it is important to consider the potential risks and take appropriate safety precautions, such as wearing personal protective equipment (PPE) and ensuring good ventilation.
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Using a heat gun
Firstly, ensure you have the right equipment. It is recommended to use a heat gun with adjustable temperature settings, so you can tailor the heat output to the specific type of plastic you are working with. Look for a heat gun that offers a balance of power, precision, and safety. Additionally, ergonomic design and safety features like automatic shut-off are important considerations.
Before using the heat gun, prepare your PLA plastic by removing any excess material and supports with a utility knife. Sand down your piece to remove ridges and create a smoother surface.
When you are ready to use the heat gun, start by testing it on a small piece of plastic to ensure you have the right temperature. Basic heat guns have fixed heat settings, while more advanced models allow you to control the temperature with a dial. Always refer to the manufacturer's guidelines for the specific plastic you are working with to avoid damaging the material.
If you are using the heat gun to smooth your PLA plastic, hold it at a reasonable distance from the piece and constantly rotate the plastic to avoid melting it in one area. Give the plastic breaks from the heat to avoid warping, and allow it to cool and solidify before moving on to the next step. You can speed up the cooling process by using the fan-only function on your heat gun if it has one.
If you are using the heat gun to reshape your PLA plastic, you can simply heat the plastic to soften it and then mould it into your desired shape. You can also use the heat gun to weld multiple pieces of PLA plastic together by heating the surfaces and joining them while they are still molten.
Finally, always allow your heat gun to cool down before putting it back into storage. Place it on a heatproof mat or stand to prevent anything from coming into contact with the hot parts of the tool.
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Frequently asked questions
PLA plastic is an eco-friendly 3D printer material made from renewable resources like corn starch.
Sanding PLA plastic is a common method to file it down. Start with 120-grit sandpaper and work your way up to 220-grit. You can also use a heat gun to restore the colour of the plastic after sanding.
Yes, you can use card/cabinet scrapers to shave the plastic instead of sanding it. This method is faster and creates a smooth surface.
You can use spot putty to fill in any low spots or rebuild minor blemishes. You can also use a variety of chemicals such as acetone, THF (Tetrahydrofuran), or DCM (DichloroMethane) to dissolve or smooth the PLA plastic.
Filing down PLA plastic can help remove rough edges and layer lines, giving the plastic a smoother and more polished appearance.
