How to Finish & Smooth 3D Printed Parts: PLA and ABS


Anyone who has ever used a 3D printer, knows the significance of print finishing for greater quality. This marvel is called post-processing, and this article strives to guide, exactly how one can have the best possible finished prints when working with PLA and ABS.

The best general methods of post-processing 3D printed parts involve sanding with different amounts of grit, vapor smoothing, using brush-on substances such as 3D Gloop and XTC 3D epoxy resin. These techniques are usually followed by using a primer spray, which prepares the surface for paint.

This is as basic as it gets. What comes next clears the reader of any doubt and ingrains all the necessary information in developing the supreme quality of their prints.

How to Finish & Smooth Your 3D Printed Parts

It would be nothing short of a dream to have prints come out of the printer all in perfection and ready to go. Unfortunately, that’s nowhere the case. The first thing that a person could notice off of a fresh print is an accumulation of layer lines.

These layer lines, which give an unnatural look to the print, are eliminated by a process called Sanding.

Sanding, being one of the most common and equally essential methods of post-processing, is usually done by applying a sandpaper of multiple grits. It’s advised to start off with smaller, around 80 grits, to remove any blemishes or imperfections and then move on to higher grits when the surface has been evened.

What will begin to look rough and dull when sanding starts, will eventually become highly refined when the process is further advanced. A wet type of fine-grit sandpaper, around 1000 grits, is applied on the print in the very end to provide a polished look.

A great assortment of grit sandpaper to go for is the Miady 120-3,000 Assorrted Grit Sandpaper. You get a very wide range of grits with this sandpaper with a total of 36 sheets (3 of each grit). They are multi-purpose sandpaper and also perfect for sanding your 3D printed objects to a great finish.

Even if all that doesn’t give you the desired look, next, there’s the prospect of using the brush-on XTC 3D. This is a two-part epoxy resin capable of providing a glossy finish.

Keeping in mind that sanding is a generic process and might have to be used in-between the procedure of applying the XTC 3D, to ensure proper smoothness. Moreover, 3D Gloop, originally used as a printing bed adhesive, also makes layers lines disappear with just one thin coat.

XTC-3D High Performance 3D Print Coating by Smooth-On is an amazing product, well-known in the 3D printing community to provide a smooth coating to a wide range of 3D printed parts. It works very well with PLA, ABS, down to even wood, plaster and paper.

It does very slightly enlarge your printed object’s dimensions and takes about 2-3 hours to fully set. This epoxy is like a warm honey, rather than those thicker epoxys out there so it can easily be brushed on.

On top of everything combined, what follows is priming and painting. This set of techniques is key in finishing off a print with terrific value.

It begins with priming, a two-coat process with drying intervals in between, to fully expose the surface of the print and avail it for painting. Again, sanding, or any other method for eliminating the layer lines, is a necessity before reaching this stage of post-processing.

Once the print is bone dry after priming, paint can be applied using either a brush or a spray, to finalize finishing. The resultant product should look extremely appealing at this moment.

Marching on to another way, when parts bigger than the build volume are needed to be formed, they are printed in steps. In the end, they are then processed first by applying a method called Gluing.

The separate parts are simply glued together to make those become one. PLA works very well with gluing when strong bonds are made between its parts.

This process is very cheap, really convenient, and requires little to no amount of prior experience or skill.

Nevertheless, the parts that are glued together won’t be as strong as the solid, individual ones.

Smoothing & Finishing Your ABS 3D Prints

Post-processing methods may vary from filament to filament. For ABS, however, there’s this one unique technique, unlike any other, that is bound to deliver highly apparent results. This is called Acetone Vapor Smoothing.

What we’ll be needing for this, is a container that’s confinable, paper towels, an aluminum foil so that the print isn’t really in contact with the Acetone, and last but not least, Acetone itself.

You can get a high-quality set of Pure Acetone – Concentrated from Amazon for a great price. You don’t want cheap acetone with additives such as some nail polish removers.

The procedure is really simple. The first step is to cover the container with the paper towels on each side. Next, we sprinkle inside some Acetone. Then, we cover the bottom of the container with the aluminum foil so our model is safe from the dangerous chemical.

Afterward, we put the print inside the container and seal it so there’s no effusion.

This is actually applicable because of the fact that Acetone melts ABS gradually, which we can use to our advantage. The process, however, is slow and may take up to several hours. Therefore, our job here is not to overdo it and this can take some time to get used to.

The tip here is that the print is still melting for quite a while even after it’s been taken out of the container. That’s why it’s important to evaluate precisely when to take it out to get the desired result, because it’ll still be melting afterward.

You can also follow this video guide below on smoothing ABS with acetone.

The Acetone vapor bath has proven to be really effective in smoothening ABS prints and there’s a huge difference between the before and after perspective.

Nevertheless, it’s not the only technique to apply. Sanding, painting, and using an epoxy, furthermore, are also great operations for the magnificent cause, along with painting.

Smoothing & Finishing Your PLA 3D Prints

While the process of Acetone smoothening is distinct for ABS, PLA has its own method of post-processing.

It’s quite convenient in PLA as well that a number of ways are able to provide significant finishing to the prints. These include pre-sanding before moving on to other techniques, applying 3D Gloop which works extremely well, and painting.

Given the fact that PLA isn’t soluble in Acetone by far, it is, however, fairly compatible with hot benzene, dioxane, and chloroform. This opens up new ways of post-processing PLA based prints.

One such possibility is polishing PLA with THF (Tetrahydrofuran).

In this process, a lint-free cloth is used along with nitrile gloves, preferably, non-latex. This cloth is dipped in the THF, and applied on the print in a circular motion, as if one were to polish their shoes.

After the total application, the print would take some time to dry so any unwanted THF could vaporize. The print now has a smooth finish and looks as good.

These substances do require a high level of safe handling and responsibility so I don’t recommend messing with some of them. You’re better off sticking with sanding and a safer substance such as XTC brush-on epoxy.

Caveats to PLA Post-Processing

An unconventional method of finishing PLA prints, would be using a heat gun.

However, there’s a caveat associated with this technique because it’s widely known that PLA isn’t heat resistant, nor can it withstand a high temperature for a prolonged period.

Therefore, using a heat gun may have the desirable results, but a certain amount of skill, and a prior experience is required to actually obtain a finished product, and not lay waste to the entire print instead.

If you are after a high-quality heat gun, your best bet is the Chandler Tool Embossing Heat Gun from Amazon. It’s UL certified, American-made and versatile for many uses.

Moreover, there’s a safety risk involved as well since the plastic will melt when the heat gun is in use, therefore, extrusion of toxic fumes may occur. That’s why it’s always recommended to work with printing in an area that’s properly ventilated.

Additional Methods of Smoothing/Finishing 3D Prints

Being a multi-faceted concept, the boundaries of post-processing are expanding rapidly, being in a tech-forward age.

The following are relatively different techniques of finishing 3D prints, capable of delivering distinguished quality.

Electroplating

The perks of electroplating are not only about the finishing, but increasing the strength of the part as well.

Materials used in this process are mostly gold, silver, nickel and chrome. However, this only works with ABS, and not PLA.

Electroplating substantially increases the overall look, finish, and the feel of the print but, it’s comparatively expensive and can require expertise in carrying it out.

Hydro Dipping

Hydro dipping is somewhat new, compared to the other techniques used in post-processing.

Also known as immersion printing, this process is an application of a design to the printed part.

This method only works to change the appearance of a part, and has nothing to do with its dimensions. Again, this is also costly and can demand skill from the user.

Post-Processing Beforehand

The procedure of finishing 3D printed parts begins even before the filament is extruded from the nozzle and onto the printing bed.

There are a number of options to be considered that influence our end product in a considerable way and greatly help in post-processing.

The print settings, the orientation of the print, the amount of build platers, all go in thought when talking about the actual surface finish of the print, that eventually leads to a big help in the post-process.

According to Maker Bot, “Surfaces printed vertically will have the smoothest finish.” They also go on to add, “Printing models in 100 micron layer resolution will result in a slightly smoother surface finish, but will take significantly longer.”

In addition, if there’s the possibility of not using any type of support material along with a raft, a brim, or even skirts, unless absolutely necessary, it’s ideal for our final print quality.

This is because these require a bit of extra post-processing which may sometimes affect the quality of the print if not handled with precision. This makes support materials a liability in the long run.

Safety Precautions with Post-Processing 3D Prints

There is indeed, a health concern affiliated with almost every aspect of 3D printing, and post-processing is no exception as well.

The process of finishing prints is vast. It involves a ton of techniques and methods applicable to achieve the desired touch and grace. However, all of those techniques may not be 100% safe and secure.

For starters, items like an X-Acto Knife is fairly common to use in post-processing. When removing support items, or any other protrusion of left-over plastic on the print, it’s encouraged to cut away from the body. A pair of gloves during this encounter greatly reduces the chances of any cuts or further injuries.

Moving on to substances such as the 3D Gloop, which is highly useful if one wants a glossy finish, it, however, comes with a whole set of potential hazards. It’s highly flammable and comes with a precaution headline that specifically asks to avoid skin contact.

It’s always recommended to work in a well-ventilated area with 3D printers overall, and that’s exactly what’s preferred when using 3D Gloop as well to eliminate the risk of inhalation of any vapors.

Furthermore, sanding also exhibits fine particles in the air, which are prone to inhalation. This is where a respirator comes in to avoid this endeavor.

Specifically speaking, ABS is almost always post-processed with Acetone, which is a highly-toxic chemical, capable of posing a great risk to human health.

Caution is always advised when operating an Acetone vapor bath as it is explosive and also flammable and able to cause irritation in the eyes, and while breathing. Again, ventilation and keen observation is a must to approach the safest possible way of finishing.

Also, breathing in the dust from sanding epoxy or coming in contact with it, is liable to sensitize the immune system and cause allergy. This could cause allergic reactions to using epoxy resins.

Therefore, gloves and a respirator, yet again, come really nifty in eliminating exposure.

Some Handy Tips for Smoothing & Post-Processing PLA & ABS

Post-processing is a time-consuming and a process that demands skill. A few pointers here and there can help straighten the procedure out and turn out highly convenient for many.

  • When priming and painting, it’s better to use both, the primer and the paint, from the same manufacturer. Otherwise, the paint runs at a risk of cracking, ultimately ruining the print.

  • When trying to remove any protrusions from a PLA print, it’s better to file it instead with small needle filers. The Tarvol 6-Piece Needle File Set from Amazon is perfect for this, made from high-carbon alloy steel. Cutting it won’t be any help since PLA is brittle, unlike other filaments such as ABS where cutting works just fine.

  • Speed matters a lot in 3D printing. Going slow when filing, or using a heat gun to finish parts, go above and beyond in producer finer, flawless detail.

  • Starting printing with a lower layer height can save you from a lot of post-processing.

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