How to Make 3D Prints Smooth

How exciting is it to print something three-dimensional! You can make everything from figurines to phone cases to acoustic guitars.

This technology is quickly advancing. In a couple of years, it’ll be normal for every household to own a 3D printer just like they own a television set. Yet, while 3D printing is definitely more exciting than 2D printing, it’s also much more complex.

There are also many steps you have to go through after printing to ensure your model has a smooth finish. Even the best FDM printer produces layer lines that can leave your model looking dull and faded.

Today, we’ll show you several ways to make sure that doesn’t happen to your 3D print. Read ahead to learn how to make 3D prints smooth and glossy.

How to Sand Down 3D Printed Parts

A fused deposition modeling (FDM) printer uses a thermoplastic PLA polymer in a filament. The printing process begins by heating the filament.

Once the filament is hot enough, it’s pushed through an extruder and deposited via the nozzle. Then, the printing starts.

After the model is printed, it’s time to remove it from the machine to begin the sanding process as follows. 

Sandpaper and Grit

Once you have your model ready, the first step is to sand the surface. Almost all polylactic acid (PLA) parts need some form of sanding. The best way to start is by using multiple grits of sandpaper.

Begin with 200 grit and work your way up to 4000 grit. Always remember to sand in a circular motion. Also, make sure to work against the grain of the layer lines, or fibers, of the work.

The best type of sandpaper is usually wet/dry or waterproof sandpaper, which is known for its black grit. They allow you to wet the sandpaper so you can cool the plastic and avoid damaging it.

Avoid Overheating

Bear in mind that sanding creates friction, which generates heat. The heat can melt the model and ruin your print.

In addition, try to avoid using power tools. These tools create vibrations that can melt the plastic and ruin the model.

Another way to avoid overheating is to frequently rinse the model in a basin or large bowl. You can even add a drop of soap into the water to help lubricate the surface.

Rinsing also cools down the work and removes tiny particles that become airborne. Inhaling these tiny particles can be a health hazard, so it’s better to get rid of them as often as you can.

Once you’re done sanding, give the model a final rinse. Leave to air dry.

How to Make 3D Prints Smooth

Check out these four techniques to learn how to make 3D prints smooth. It’s worth mentioning that no matter which method you use, you may lose fine detailing and sharp edges.

One way around this is to design your model into sub-assemblies. Next, smooth each piece on its own before gluing them together to create a professional-looking 3D print.

Keep reading to find out which method works best for you and your 3D models.

  1. Polishing Compounds

Sanding by itself can never completely get rid of layer lines. To do that, you need to apply a polishing compound. This compound fills in the tiny spaces between layer lines for a shiny, smooth finish.

You can find polishing compounds sold as bar-solid shapes. Each one comes in a different grade, just like sandpaper.

To use polishing compounds, wipe some on any type of attachment for rotary tools, like a buffer wheel. Then, apply them to the plastic.

Pro tip: when you’re applying a buffer wheel, move at a slow pace. Buffing generates friction, which produces heat, which can damage the plastic.

  1. Primer Spray Paint

A second method you can use to smooth out your 3D prints is to use sandable high-fill primer spray paints. You can find them in almost any hardware store.

First, begin by spraying a thin coat of primer. Next, sand the layer of primer spray until the plastic becomes smooth. Once you’re done, you’ll hardly notice any of the layer lines.

Pro tip: always use products from the same manufacturer. It’ll give your model an even finish without damaging the surface.

Also, avoid combining enamels with acrylics. This will only increase the risk of damaging the work and even causing the paint to crack.

  1. Heat Gun

A second way to smooth PLA parts is by applying high heat levels for a short period. It gets quick results, but it’s a bit harder to master than the first two techniques.

The problem with using heat guns is that it’s hard to spread the heat evenly on the surface. If the heat isn’t spread evenly, the model will start to bubble. Remember to keep your hands moving over the model to avoid damaging your model.

We found that when we used sanded PLA, we were able to control the heat level. Not only that, but the whole process took less time compared with a model that wasn’t sanded.

Pro-tip: heating PLA parts release harmful fumes. So, make sure you work in a well-ventilated area. Wearing proper respiratory protection can also provide adequate protection against these fumes.

  1. Chemical Treatments

There are four main chemical treatments used in smoothing 3D print models. Two types, namely Acetone and M.E.K., don’t really work on PLA parts.

The other two, THF and ethyl acetate, do a much better job. Yet, they’re considered hazardous materials and should be used with extreme caution.

Tetrahydrofuran (THF) is a flammable liquid that can cause skin irritations and other health issues. It’s even been classified as H351, or ‘suspected of causing cancer.’

Ethyl acetate is typically found in nail polish remover and glue. Like THF, it’s a highly flammable solvent and can irritate the eyes and lungs.

Pro tip: Wearing safety gear, like goggles, respiratory protection, and PVA gloves, is a must. They should be worn at all times when handling these chemicals. Also, make sure there’s proper ventilation anytime you do any chemical smoothing.

Conclusion

Learning how to make 3D prints smooth and shiny takes time. Try each of the methods we mentioned above and see which one gives your model a glossy, flawless surface.

We recommend you print several versions of the same model. Then, practice a different smoothing technique on each one.

Once you find your groove, try it on other models. You’ll be creating smooth, professional-looking 3D printing masterpieces in no time!

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