How to Smooth 3D Prints: Sanding PLA & More

Even though FDM is one of the more affordable 3D printing technologies, the printed parts still need to undergo post-processing procedures to improve the models’ aesthetics. The post-processing techniques can occasionally be challenging and disorganized.

Smoothing 3D prints requires effort, which those who use FDM printers for 3D printing must accept. The work becomes even more challenging when the models have intricate details or complex geometry. One must learn many techniques to make parts aesthetically pleasing to the eye.

When compared to 2D printers, where the work is completed when the paper comes out of the machine, 3D printing may appear to be a simple task. But this is not the case. A completely different definition applies to 3D printing.

Even after a 3D printer has finished its work, post-processing steps like sanding 3D prints, removing support, etc., are necessary.

The most frequently asked question is how to smooth 3D prints. Let’s talk about some 3D print smoothing techniques. By using these techniques, it is possible to enhance the appearance of 3D-printed models significantly.

How to Smooth 3D Prints: Sanding PLA & More Methods for Printing Smooth Parts

It’s best to plan ahead and print parts that will be simple to sand to save time and effort later. How you store your filament and the slicer settings you use can impact how much sanding your prints need.

Like most plastics, PLA is hygroscopic, which means it takes in environmental moisture. A rough, erratic finish is left behind when humid PLA passes through the printer’s nozzle. Additionally, it leaves behind material strings. Spools are not a problem because they are shipped vacuum-packed with desiccant. However, more than a few weeks old spools should be dried before printing or kept in a dry environment.

Even how your 3D model is exported from your design software can affect the surface quality of the printed object.

Keep the chord height much lower than the print layer height when exporting STL files. The chord height is the most that the STL file can deviate from the source model. A lower value indicates that the model will contain more polygons, reducing the number of faceted corners on curved surfaces.

You won’t be able to alter the chord height of an STL file you downloaded from a sharing website like Thingiverse. You shouldn’t be concerned because STL files on repositories typically have a good resolution.

How to Smooth 3D Prints: Sanding PLA & More Slicer Settings

Numerous settings can be used to lessen the amount of sanding necessary. To name a few:

• Object orientation: The direction of the print has an impact on surface quality. Overhang areas require support, which results in a very rough surface. Print with the excellent side up if possible to ensure no visible signs of support.
• Layer height: For within reason, layer height should be set to your machine’s more acceptable settings. Although it can lengthen print times, a shallow layer height will result in a smoother finish. They are more tolerant of coarse layers for shapes with vertical walls and flat tops than they are for shapes with angled walls or domed tops.
• Wall thickness: The wall’s thickness is crucial for sanding. If you sand too deeply, it’s a good idea to have a bit of extra wall thickness. Otherwise, you risk leaving a hole or ripping the filament into pieces. A thin wall will deflect as you sand, leaving an infill imprint pattern. Also, remember that you’ll be tightly gripping the component; a delicate piece can easily break while being handled.
• Print speed: If the print speed is set too quickly, the printer may vibrate, leaving a mark on the print that others can see. To lessen vibration, lower the machine’s acceleration settings.

A smoother 3D print can also be achieved with special slicer features. The top layers of the print are smoothed using an ” ironing ” feature available in Ultimaker Cura and PrusaSlicer. The high points are smeared flat by running the printer nozzle over the top layer. Although you might need to play around with the settings, it can help to smooth that top layer.

How to Smooth 3D Prints: Sanding PLA & More Why Sand?

Even if you’ve done everything, sanding is frequently necessary to obtain a superior finish. But why sand when it can be so labor-intensive?

• Getting rid of rough edges and surfaces is crucial. Even though PLA isn’t particularly sharp, it can still be uncomfortable when used in wearable applications like costumes or prosthetics. Feel the entire component with your hands, then use a file or coarse sandpaper to remove anything sharp. If you do this first, it is simpler to aggressively sand in subsequent steps without tearing sandpaper.
• If you are putting together mechanical parts, precision is crucial. Forms like cylinders and flats should be kept. Based on their intended use, shafts and holes require special clearances. Still, they might need to be adjusted due to your printer’s accuracy. Test fitting components and marking areas that need to be removed should be done both before and during sanding.
• A print’s appearance matters, especially for functional items like movie props or marketing samples. Still, it also matters for pride in one’s own handiwork. In each of these scenarios, getting rid of layer lines is crucial.

How to Smooth 3D Prints: Sanding PLA & More Needed Supplies

Whatever your motivations for sanding, you should begin by quickly removing any existing material. This quickly completes the majority of the shaping.

There are different grit types of sandpaper (levels of roughness). Coarse grits (60 or smaller) are used for quick material removal. 60 to 80 medium grits are used for smoothing before priming. For priming surfaces for painting, use fine grits (100 to 120). Between coats of paint, very fine grits (150 to 220) can be applied. After painting, extra-fine (400 grit and higher) is used for polishing and shining.

Sand frequently falls off the paper when using cheaper products because the adhesives are subpar. Sandpaper with variable grit sizes is even worse. A single coarse grain can leave a deep scratch on a fine paper, forcing you to resume rough sanding. Avoid keeping fine and course papers together because of this. Also, cleaning a part to eliminate any remaining coarse grains is crucial before switching to a finer grit.

DIY Tools

Because of their geometry, some parts may need specialized equipment to sand specific surfaces or difficult-to-reach areas. Fortunately, there are plenty of inexpensive DIY options, so this need not be expensive. For instance, sandpaper can be used to make a sanding block by wrapping it around a piece of hard material, typically wood.

Between the sandpaper and the block, place a foam, cloth, or rubber pad to help the paper adapt to the shape of the component. This sanding pad removes STL file artifacts and softens sharp edges. Sandpaper can adapt to the shape of the part with thicker pads. However, be aware that the paper may rip if you push too hard while sanding sharp corners with a thick, soft pad.

Simply folding a piece of sandpaper works wonders for deep grooves and corners. To enlarge or smooth out holes, roll sandpaper around a dowel. Naturally, you can print your own sanding tools as well.

Needed Equipment

Files are a practical purchase regarding sanding tools for confined spaces. PLA won’t damage files, but it can clog the file teeth, so it’s a good idea to keep a file card—a wire brush for cleaning files—on hand. A tack cloth, which is used to clean an object before priming or painting, is an additional helpful tool to have on hand. Dust from sanding needs to be disposed of somewhere.

POWER TOOLS

Power tools are excellent for quickly removing material from sizable areas. Although it takes some practice, this can save a ton of time. If the pressure or speed is too high, friction will eventually soften or melt PLA, especially if the walls are thin or the part is small.

You should begin with less critical areas to gauge how quickly things heat up. Sand an area briefly. It’s too hot if the part becomes less smooth as you sand it. It may help to have a fan blowing, but the main thing is to keep the tool moving.

OTHER MATERIALS

Fillers and primers are crucial to conceal deep layer lines, gaps, and other low-lying flaws. Wood putty or similar fillers can be used to close more significant gaps. Primers are porous paint that adheres well to the base material.

There are various kinds of primers to be aware of. Sandable primers cover surfaces thickly to smooth them. For large projects or spot filling, brush-on primers are more affordable and effective. Primer sprays are practical and don’t leave brush strokes.

Finishing Technique

Peaks and valleys can be seen on a part’s as-printed surface. Print layers, support material, printer artifacts, or STL nodes make up the peaks. The valleys are the gaps and spaces between the layers brought on by nozzle flow interruptions.

Nearly all of the peaks can be eliminated with an aggressive first pass with coarse sandpaper. Scratches left over from the previous step will be removed by making additional passes with finer paper.

Finer grits can be used with wet sanding. As primer and fillers can stick to the paper and clog the grit, using a little water to help remove debris and prevent the paper from becoming gummed up.

But most importantly, always protect your eyes and wear a dust mask when sanding!

The cosmetic finishing level

How do you recognize when you’ve finished? What exactly does “finish level” mean? Consider the intended use and the size of a defect that could go unnoticed. The average human eye can recognize a feature that is 0.4 – 0.3 mm in height from a meter distance. This ratio can determine the minimum flaw size for each use case.

Always check the finishing parts in good lighting and after the paint has thoroughly dried to help determine how much more is needed. As paint dries, it shrinks and reveals flaws.

How to Smooth 3D Prints: Sanding PLA & More Step-by-Step Overview

Use the following summary as a reference to apply what you’ve learned to your subsequent project:

1. Use an STL file with fidelity appropriate for your use case.
2. Print components using the best slicer settings.
3. Before sanding, check the part for print flaws, jagged edges, or rough surfaces.
4. Start with coarse sandpaper or files to smooth any potentially dangerous edges and surfaces.
5. Before assembling any parts, test-fit them while putting any moving parts through their full range of motion. As needed to achieve the desired fit, add rough sand.
6. Sand all surfaces with 60-grit sandpaper. Take away every peak to reach the valley. Gaps and profound valleys may still exist.
7. Fill holes, exposed infill, or other print flaws using a putty-like filler. Dry the putty.
8. All putty repairs should be sanded with 60-grit sandpaper to eliminate extra material.
9. Sand every surface using 100-grit paper. Continue until any severe abrasions caused by the 60 grit are eliminated.
10. To paint components evenly with one coat, use a primer. Permit drying.
11. Check each element under good lighting for flaws and noticeable layer lines.
12. With finer sandpaper, refinish the parts, paying close attention to trouble spots.
13. Once more, prime each component, then let it dry.
14. Repeat the first three steps until the parts meet your standards for quality.
15. Your components should now be sanded and prepared for painting.

Sanding Other Materials

You can experiment with other materials after you have mastered sanding PLA. How apart is sanded depends on variations in hardness, grain, and softening temperature.

• Popular printing filaments ABS and PETG can be vapor smoothed, which involves using a solvent to dissolve the surface material momentarily. Otherwise, these substances resemble PLA.
• Rubbery materials often smear when excessive force is used. The best sanding technique is quick, light strokes. Use wet sanding to prevent the material from grabbing and clogging adhesive materials. If the rubber wants to catch the grit, use finer sandpaper.
• Sanding fibrous materials, such as wood and composite filaments, should be done with the grain. If you don’t wear gloves, materials like carbon fiber, kevlar, and fiberglass can sting you with sharp edges. Although composite fibers are prevented from becoming airborne during wet sanding, you should still always wear a dust mask.
• Metals can achieve a high luster but require more time to sand. Over time, oxidation can dull some metals, including copper and aluminum. You can add a clear coat to stop oxidation or polish from bringing back the shine.
• Medium grit sandpaper makes high-density urethane foam easy to work with. Keep the vacuum running because dust will continue to accumulate everywhere and in the air. Before spending too much time on a part, test it with scrap material to see if the paint will melt polystyrene foam.

How to Smooth 3D Prints: Sanding PLA & More Alternatives to Sanding

If all of this seems like too much work for you. There are a few other ways to smooth PLA. The outer surface can be carefully melted with a soldering iron or woodburning tool to produce a low-effort smoothness.

Some of these alternative methods can be messy and call for adequate ventilation. For instance, epoxy or UV resins can be applied to the part, leaving a thick, hard shell. However, you shouldn’t breathe certain coatings for an extended period. Start your upcoming project right away and start creating dust! After a few builds, you’ll eventually strike the ideal balance between time commitment and finish quality.

How do you smooth your 3D prints? What is the best method you tried?