If you’ve ever pulled a fresh 3D print off the build plate, you know the job isn’t quite finished yet. Those layer lines, support marks, and rough edges can keep your part from looking professional or performing at its best. That’s where 3D printing post-processing comes in. But what processes are generally used in 3D printing post-processing? In this guide, we’ll walk you through everything you need to know about transforming your 3D prints from good to great.
Why 3D Printing Post-Processing Matters
Before diving into the specific processes, let’s talk about why post-processing is so important. 3D printers build parts layer by layer, which naturally creates a textured surface—especially with lower print resolutions. If your part needed supports, you’ll likely have extra imperfections where those supports were attached. Post-processing fixes these issues and offers even more benefits:
- Smoother Surfaces: Reduces the appearance of print layers and refinements for a polished look.
- Stronger Parts: Reinforces prints to add strength and durability for functional use.
- Added Functionality: Improves properties like UV resistance, weather resistance, and conductivity.
- Aesthetic Finishing: Transforms the surface appearance to create visually striking parts.
Every 3D print can benefit from some form of post-processing, whether it’s a simple sanding job or a more complex chemical treatment. Let’s explore the main categories and processes.
The First Step: Support Removal
Before any other post-processing can begin, you’ll probably need to remove support structures. Unless you’ve optimized your print for supportless 3D printing, those supports are essential during the printing process but become unnecessary once the job is done.
Most supports can be snapped off by hand, but even well-designed supports leave behind imperfections. That’s why it’s recommended to post-process the entire part after support removal to smooth out these areas. For a cleaner solution, dual extrusion printers can use soluble supports that disintegrate in water, leaving no trace behind—perfect for parts where post-processing might be tricky.
3D Printing Post-Processing Categories
All post-processing methods fall into three main categories: subtractive, additive, and property changing. Each category has its own set of processes, and choosing the right one depends on your part’s material, geometry, and desired outcome.
Subtractive Post-Processing: Removing Material for Smoothness
Subtractive post-processing is the most common category, and as the name suggests, it involves removing material from the part’s surface to make it more uniform and smoother. Here are the key processes in this category:
Sanding & Polishing
Difficulty: Low to Medium | Smoothness: High
Sanding and polishing are the workhorses of 3D print post-processing. Both techniques remove surface layers using abrasive materials, but they differ in execution. Sanding uses coarser grit sandpaper and tools to tackle larger blemishes like support remnants or print irregularities, reducing the visibility of those pesky layer lines. However, sanding leaves a gritty (though more uniform) surface, and very coarse sandpaper can create new scratches.
Polishing takes over after sanding, using finer sandpaper, steel wool, polishing paste, or cloth to produce an even smoother surface. The best part? These methods are simple and affordable, making them accessible to hobbyists and professionals alike. The downside? They’re labor-intensive, especially for larger parts or batches, and they struggle with hard-to-reach cavities.
Tumbling
Difficulty: Medium | Smoothness: Medium to High
Tumbling is like a spa day for your 3D prints, but with a rough-and-tumble twist. A tumbling machine consists of a vibrating vat filled with lubricating fluid and abrasive media—specialized stones that wear down objects based on their size, shape, and hardness as they tumble together. Just place your 3D printed part in the vat, set the timer, and let the machine do the work.
Tumbling is great for batch processing multiple parts at once, and it works for larger parts too, as long as you have a big enough machine. However, it requires some expertise to pair the right abrasive media with your part and determine the correct processing time. Keep in mind that complex shapes might lose detail, and sharp edges can become slightly rounded.
Abrasive Blasting (Sand Blasting)
Difficulty: Medium | Smoothness: Medium
Abrasive blasting, or sand blasting, blasts abrasive material onto 3D printed parts at high pressure. For large parts, this can be done in an open environment, but smaller parts usually go into a containment chamber that collects and reuses the abrasive material. You can choose from a range of grits depending on your part’s geometry and desired finish—sand is common, but plastic beads can also be used for different results.
This method is less effective on very rough parts or those with high layer heights, and it only treats surfaces reachable by the blasting stream, so complex geometries and cavities might be out of luck. It’s also slower for processing multiple parts simultaneously since the blasting tool can only treat limited areas at a time.
CNC Machining (Milling)
Difficulty: High | Smoothness: Very High
CNC milling is like the precision sculptor of post-processing. It uses a computer-programmable drill that moves (and sometimes rotates) in three axes to carve out geometries, using G-Code just like 3D printers, but with a milling bit instead of a filament extruder. It’s highly accurate, with tolerances ranging from 0.005” to 0.00005”.
While it’s not cost-effective to mill an entire 3D print, it’s perfect for smoothing specific areas that need extreme precision. You can even 3D print a part in a rough finish and then mill it to perfection, saving material in the process. Just note that CNC machining can’t produce certain geometries and wastes more material than 3D printing.
Chemical Dipping
Difficulty: High | Smoothness: High
Chemical dipping, or acid dipping, involves submerging parts in a chemical bath that eats away at the surface. It uses caustic materials like lye, sodium hydroxide, or dichloromethane, so it should only be done by experts in facilities with proper safety features. The key is choosing the right chemical for your 3D print’s material— it needs to be abrasive to the print material.
Timing is everything here: too short, and the part won’t be smooth enough; too long, and you might ruin it entirely. You also need to watch out for air bubbles trapped inside the print, which can prevent the chemical from treating the surface— gently moving the part in the bath helps release these bubbles. Chemical dipping is ideal for complex geometries since it treats all surfaces simultaneously, but the size of the container limits the part dimensions you can process.
Additive Post-Processing: Adding Material for Strength and Smoothness
Additive post-processing puts additional material directly onto printed parts, making it highly efficient for smoothing while adding strength and other mechanical properties. Let’s explore these processes:
Filling
Difficulty: Low to Medium | Smoothness: Medium to High
Filling is like spackling a wall, but for 3D prints. It uses a thick adhesive compound, usually a paste, to fill in notches like the tiny gaps between layers. It’s often used as a first step before sanding or adding more layers. You can choose from a wide range of fillers: paste fillers (like wood fillers or household spackle) are easy to spread and smooth with light sanding; spray fillers are simple to apply but only provide a thin, rougher coating; and resin fillers, which cure either by mixing with a hardener or UV exposure, offer more robustness.
Resin fillers come with various viscosities, cure speeds, and advanced features like UV resistance and high heat deflection temperatures. Some UV-cured fillers can be set in the sun, while others need a specialized UV chamber. Just remember to wear gloves, cover your skin, and keep the workspace well-ventilated when using resins.
Priming
Difficulty: Low | Smoothness: Low to Medium
Primers are the warm-up act for your post-processing routine. They prepare 3D-printed parts for subsequent layers by pre-treating the surface for better adhesion. They’re less viscous than fillers and only smooth very small imperfections, so their main job is to get the surface ready.
Primers come in spray or brush form, with spray primer usually producing a more even coating. For best results, first reduce imperfections and layer notches with sanding or filling, then use a primer made for plastic adhesion that’s suitable for the materials you’ll apply later. Let the primer set for 24 hours or as directed.