How to Smooth 3D Prints

Perhaps the most notorious characteristic of 3D prints is their layer lines, the bumpy texture formed by the layer-over-layer manufacturing style of a 3D printer. 

Unfortunately, layer lines prevent a model from appearing smooth and glossy, so they’re not desirable when printing display pieces, like a cosplay model or trophy. While avoiding layer lines during the printing process is almost impossible, there are a few ways you can remove the layer lines after printing.

Layer smoothing describes blending the exterior layers of a 3D printed model (post-printing) so that they’re more cohesive. This makes models look smoother because the separation of the layers isn’t noticeable from the outside.

Depending on the type (material) of filament you printed your model in, you can layer smooth models in a few ways such as using a special solvent chemical, sanding, and layer melting. 

If you’re looking for the smoothest surface, a chemical solvent or surface coating should work best, but sanding and surface melting are the more convenient options. 

If you want to learn about the different ways you can smooth your models, no matter what material they’re 3D printed in, then read on!

What Are the Advantages of Smoothing 3D Prints?

Before we dive into the actual methods of smoothing 3D prints, it’s important to go over how layer smoothing can help you.

Of course, the main benefit of layer smoothing is that parts appear smoother and glossier. As we’ve mentioned, this is super useful for printing models that you want to put on display. However, layer smoothing also makes it easier to paint 3D models because paints, like acrylic paint, stick better to the sides of a 3D printed model when they are smooth and not rough and porous.

Source: Youtube 3DWithUs

Visual appearance isn’t the only advantage of layer smoothing, though. 

In fact, layer smoothing 3D prints can actually strengthen prints because blending the exterior layer lines together improves the layer-to-layer adhesion of the model. In turn, this makes layer smoothed models less brittle and overall stronger, which is super useful if you’re printing parts that will face physical stresses, such as a gear or a lever.

Now that we’ve discussed some benefits of layer smoothing, let’s get into the options and methods!

PLA Smoothing

In this section on layer smoothing processes, we’ll go over some of the most popular methods to smooth out parts printed in PLA filament, such as sanding, chemical smoothing, and more. 

It’s worth noting that many of these methods work on other materials too, like PETG, nylon, and more! 

Removing Excess Material

The first layer smoothing method we have is removing excess material. This method doesn’t exactly smooth out the layers of a 3D print, but it’s still vital to achieving a visually appealing print and you should do it after every print.

So, what does the process entail? Well, you’ll want to take any unwanted bits off of your print.

The first step in doing so is by taking off any of the slicer-generated features, like support structures, rafts, or brims. These features aren’t part of your model and only exist to assist with the printing process.

Source: Youtube by CNC Kitchen

You should also remove any byproducts of over-extrusion on your prints, such as “zits” or “blobs”. 

If you’re not familiar with these rather 3D-printing-slang terms, zits and blobs describe tiny pieces of extra filament that have been accidentally extruded onto a model. They are the result of a slightly miscalibrated extruder and leave a rough exterior surface on prints that only make the layer lines easier to see.

You can almost always take off the larger unwanted pieces of plastic, such as the main part of a brim, off your model by hand. However, for the smaller bits, like a tiny sliver of your brim or a small zit, a utility knife or rotary tool can help get the job done.

Sanding

Sanding is easily one of the most popular ways you can smooth the layer lines of your PLA print, as well as parts printed in other materials. 

As you probably know, sanding involves grinding a gritted (textured) paper against the exterior surfaces of a part to smooth them out. While sanding is used for all types of parts (e.g. wood, metal), it’s especially useful for smoothing 3D prints because it helps blend the different layer lines so the separation of the layers is less visible.

But what does “blend the layers together” actually mean? 

Well, we can visualize the different layers of a 3D print by putting two fingers together; you’ll notice that they’re not super even or flush vertically. When you sand a model, though, the gritted texture of the paper will remove any plastic from the surface that’s being sanded until it’s flush and smooth.

Source: Youtube 3D Printed Props

Moreover, when you rub sandpaper of a certain grit (roughness) on a model, the part will eventually match the level of smoothness of the piece of sandpaper. We suggest sanding your model by starting with a piece of low-grit (rougher) sandpaper and incrementally working your way down to a higher-grit (finer and smoother) piece that will yield a super smooth model.

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No matter how fine your piece of sandpaper is, though, don’t sand too much in one area because it could remove too much plastic, hurting the model’s dimensional accuracy. 

Another tip is to sand a model evenly throughout so that each surface has a similar level of smoothness. While sanding can be a meticulous and slow process, using an electric sander over your hands is a great way to speed up the process.

Wet Sanding

While it’s not an entirely different form of layer smoothing, wet sanding is also worth covering, and it’s a very specific form of sanding. Wet sanding entails dipping your sandpaper in water in between uses.

The water acts as a lubricant for the sandpaper so it flows smoother when grinded against 3D printed models. On top of making it easier to sand models, wet sanding is also considered a more effective method of smoothing compared to traditional smoothing because you can achieve smoother prints with the water lubricating the grinding process.

Of course, it’s also worth pointing out that the use of water also increases the longevity of each piece of sandpaper because any plastic stuck between the grits on the paper will be released into the water. Moreover, the added lubrication due to the liquid will make the sandpaper pieces less likely to break down and wear out as fast.

Source: Youtube 3D Printed Props

Additionally, wet sanding reduces the mess of the sanding process. That’s because when you dip the sandpaper into the bowl of water after grinding it against the 3D printed part, the removed plastic releases from the paper into the water. This way the excess plastic doesn’t get all over the floor or table where you’re sanding.

Like with regular sanding, it’s recommended to start with a rougher piece of sandpaper and work your way down to a super fine piece. However, it’s also suggested to switch out your water bowl a few times, especially when performing long sanding processes for larger models.

Surface Melting

When you heat up a piece of chocolate or a marshmallow, you’ve probably noticed that it looks super smooth and glossy right as it’s melting. The same can be said for PLA prints, and surface melting is another way to smooth out 3D prints. 

This method entails using heat to soften the exterior of a model to make it look smooth and then letting it cool this way.

Source: Youtube Tinkerine

While you should be able to surface melt prints made of basically any material, PLA is a particularly easy one to work with given the filament’s low melting and glass transition temperature. Moreover, most people employ a heat gun or hairdryer to do the job as both tools produce ample heat to melt the exterior surface of a PLA model without burning it or significantly deforming the entire model.

While it’s hard to say how much heat will yield the best results, one common method of surface melting is by directing a heat gun or hairdryer up and holding models above the heat for small amounts of time. And then, continue this process in small intervals until you achieve the level of smoothness you’re looking for. 

Remember not to keep your prints under too much heat though as they could deform.

Surface Coating

As we discussed, smoothing a 3D print entails making the model’s surfaces appear smoother, but this process doesn’t always have to be done by blending the layer lines together. 

Surface coating is a method that involves adding layers of paint or other substances to the exterior surface of your 3D printed model to make the part appear smoother.

There are many different ways you can go about surface coating your model, but, for basically any option, a coating of filler primer is usually advised. Filler primer is a type of paint that helps fill (hence the name) the small gaps in an object, and there are many on 3D prints which are usually very porous.

After a coating or two of filler, you can spray paint your model to make it look smoother and this also gives you the opportunity to change its color. For this process, you’ll want to make wide strokes with the spray can a few feet back from your model and continue until the entire model is painted. If you’re not a big fan of spray paint can, an airbrush (or air eraser) may be the better option for you as it’s a little more precise.

Then, give the first real coating a few hours to dry and repeat until you have two or three coatings of your paint. Finally, you’ll want to apply a thin layer of clear spray paint as this will give your model a shine and make it look extra smooth.

Different from the spray paint method, another way you can surface coat a 3D printed model to make it look smoother is by using epoxy resin. Epoxy resin is a clear substance that you can paint onto models to give them a shiny and smooth finish. It’s best to apply it very thick onto your models to ensure that they come out very smooth and you should use a heat gun to harden the resin and solidify its position on your model.

Of course, there are some other types of coatings you can add to your PLA prints too, but not all of them work the same way. In the next section, we’ll go over another set of substances you can apply to models but they yield smoother results a bit differently than paints and epoxy.

Chemical Smoothing

Solvents are special chemicals that can dissolve or melt certain materials. Often called vapor smoothing or chemical smoothing, you apply certain solvents to the exterior of a 3D print to dissolve or soften the outside layers of the model. After a few minutes, your print will have a super smooth and glossy finish.

It’s worth mentioning that chemical smoothing is, by far, one of the most effective layer smoothing techniques on this list. 

So how smooth are the prints? 

Once completely layer smoothed, others might not even be able to tell you 3D printed the model because the layers lines are basically indistinguishable. 

Unfortunately, there aren’t too many chemicals that act as solvents for PLA plastic, but there are a few, including isopropyl alcohol (IPA), caustic soda, and certain mixtures, such as XTC-3D. You can apply them to your model by spraying them in a vapor form or using a brush to paint them on. 

Source: Youtube Smooth-On using XTC-3D

No matter how you do it, it’s best to coat the entire model with the substance, not using too much of the solvent in any one place as you want a uniform smooth appearance throughout the model.

Make sure that you also are following the proper safety procedures when applying the chemicals. Certain solvents for PLA aren’t super healthy to inhale or otherwise be around, so wearing gloves and maybe even a mask is suggested. We also advise you to only apply the solvents to your model in an outdoor environment so the chemicals don’t affect the air quality.

ABS Smoothing

Our next section covers how you can layer smooth parts printed in ABS, another filament material. Of course, for parts printed in this material, you can use almost all of the same techniques as we’ve listed for PLA smoothing, such as sanding, wet sanding, and an air eraser. 

However, there’s one more way you can smooth ABS that’s not super effective for PLA, which we’ll talk about in the next section.

Acetone Vapor Smoothing

As ABS is chemically different from PLA, different solvents work better with the material. The most notable one is acetone, the same chemical in nail polish remover and paint remover. 

Acetone works super well for smoothing the layers on parts printed in ABS filament, and, once applied to a model, the layers will dissolve within minutes, leaving only the super shiny and smooth finish on the outside of the model.

But how do you apply acetone to an ABS model? 

Source: Youtube Prusa 3D by Josef Prusa

Well, you can use a brush and coat the model in the solvent substance. However, you’ll have to do a few rounds of painting to ensure you get the bottom of the model too.

However, the more popular method is by heating the acetone, which is usually in liquid form, to turn it into a vapor and then trapping the acetone vapors in a contained space with your print. The vapors are super effective with dissolving the layers evenly because you’re not manually adding the substance to the surfaces, which leaves a lot of room for error.

Is Acetone Toxic?

A common concern with using acetone as a smoothing chemical is the safety of the material. Unfortunately, acetone is, in fact, a toxic chemical, and you should do your best to not inhale, touch, or otherwise contact the chemical, no matter if it’s in a liquid or vapor form.

Additionally, we advise you not to put any sort of food or liquid in a print that’s been smoothed with acetone. Of course, doing so likely won’t cause any issues, but there’s always a risk so be careful.

Conclusion

Overall, there are many different ways you can achieve a smooth finish on your prints, whether they’re PLA, ABS, or another plastic.

If you’re looking for the smoothest surface, a chemical solvent or surface coating should work best, but sanding and surface melting are the more convenient options. 

No matter what method you choose, though, we wish you luck on your 3D printing endeavors and hope your models come out very smooth!

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