3D printing produces objects with a recognizable layered texture. While this can be part of the appeal for some applications, a smooth surface finish is usually more desirable for 3D prints intended to replicate conventional manufactured objects. Luckily, there are various methods available to process raw 3D printed parts into smooth, polished products.
With the right techniques, you can easily transform your 3D prints from rough to refined. A smoothed surface not only looks better, but can also improve durability and enable painting or other post-processing. This beginner’s guide covers everything you need to know to smooth PLA, ABS, and other common 3D printing materials.
Why Smooth a 3D Print?
Fresh off the print bed, 3D printed objects exhibit a striated texture from the layered printing process. While this can be minimized with very fine layer heights, some unevenness always remains. Parts also have visible print lines, gaps, and imperfections.
Smoothing eliminates these issues by melting the print layers together into one uniform piece. This removes the streaks and creates an even surface ideal for painting or vapor polishing. Smoothing is especially beneficial for 3D prints intended to replicate production items, like figurines, props, tools, and functional components.
Common reasons to smooth a print include:
- Improving overall appearance with a flawless, polished finish.
- Removing visible layer lines and print imperfections.
- Closing small gaps or holes on the surface.
- Allowing application of paint, vapor treatments, or other coatings.
- Strengthening the part by fusing layers together.
Just a little smoothing can make a big difference in print quality. It’s an essential finishing technique for refining 3D printed objects.
Materials That Can Be Smoothed
Smoothing works by melting the outer surface of the print so the layers reflow together. This requires the printing material to become soft and malleable when heated. ABS and PLA plastics, the most popular FDM 3D printing filaments, both smooth very well.
Other materials that can be smoothed:
- PLA blends – PLA mixed with additives like wood, metal, glow-in-the-dark, elastic, etc.
- ABS blends – ABS mixed with additives.
- PETG – A durable, flexible option similar to ABS.
- ASA – UV-resistant ABS alternative.
- PolySmooth – Plastic formulated specifically for smoothing.
- Nylon – Melts at higher temps than other plastics.
- TPU – A flexible filament.
Most standard FDM printing materials are fine, but avoid any with additives that could hinder melting, like carbon fiber or glass fiber reinforced plastics. You also can’t smooth SLA 3D printed resin parts – they require different finishing processes.
Now let’s look at various methods for smoothing prints using these compatible materials.
Smoothing 3D Prints with Solvents
One of the easiest ways to smooth 3D printed parts is by applying solvents. When liquid solvents soak into a plastic print, they partially melt the surface layers, eliminating print lines and imperfections.
Acetone is a common solvent used for ABS prints. It quickly dissolves the outer surface of the ABS into a liquid state that reflows together as the acetone evaporates. Using acetone is as simple as rubbing the print with an acetone-soaked rag. For deeper smoothing, the print can be submerged in an acetone bath.
For PLA prints, ethyl acetate works in much the same way as acetone does for ABS. It melts the surface allowing the layers to blend together. Isopropyl alcohol can also be used but is slower and less effective than ethyl acetate.
There are commercial solvent pastes and gels available too, like XTC-3D Smoothing Agent and Polymaker PolySmooth. These are formulated especially for 3D print smoothing and give good, consistent results.
Pros of using solvents:
- Very simple, accessible method.
- Smooths quickly with minimal effort.
- Ethyl acetate is inexpensive and widely available.
Cons of solvent smoothing:
- Acetone is toxic and requires proper ventilation.
- Can result in excessive melting if overapplied.
- Solvent odor may linger in the print.
- Smoothing is limited only to the surface.
Solvent smoothing works very well, but does have some downsides. Using the right amount of solvent and smoothing in stages can help control the results.
Heat Smoothing 3D Prints
You can also smooth 3D prints using just heat – no solvents required. Heated vapor smoothing is an advanced option, but a simple heat gun or woodburning tool allows basic smoothing too.
Here’s how to smooth a print with heat:
- Heat up the print surface by gently sweeping a heat gun or woodburning tool over it. Apply heat until the plastic starts to become glossy.
- Once hot enough, the layers will begin to melt together into a smooth, shiny surface. Slowly blend the melted plastic with the heat tool.
- Allow the print to cool fully before handling. Repeated heating and blending may be necessary for full smoothing.
This technique takes some practice to master heating the plastic to just the right temperature. Lower temps reduce risk of deformation. Consider testing on scrap prints first.
Pros of heat smoothing:
- Avoids the VOC fumes and cleanup of solvents.
- Heats and reflows the full layer depth, not just the surface.
- Results in very smooth print with glossy finish.
Cons of heat smoothing:
- Risk of overheating and distorting details.
- Requires careful temperature control.
- Not as quick and easy as solvent smoothing.
With some trial and error, heat can be an effective way to smooth prints without chemicals. For basic smoothing, a simple woodburning tool is inexpensive, accessible, and easy to control.
Vapor Smoothing for Advanced Results
The most advanced smoothing method uses heated vapor. Vapor smoothing exposes the print to solvent vapor that instantly melts the outer surface. The results are stunning – a glassy smooth finish and professional polish.
Two common vapor smoothing options are:
Cold vapor smoothing – The print is suspended above a small volume of solvent like acetone or ethyl acetate. The vapors gradually smooth the print over several hours.
Thermal vapor smoothing – The print is placed in an enclosed chamber filled with solvent vapor heated 30-80C above the boiling point. The hot vapor smooths the print completely in only 10-30 minutes.
Vapor smoothing requires either a DIY chamber or purchased device. For occasional smoothing, a simple cold vapor bath in a sealed container works well. Prosumers who print frequently justify investing in a thermal vapor polisher for fast, reliable results.
Pros of vapor smoothing:
- Produces exceptional print quality and polished finish.
- Smooths difficult-to-reach corners and recesses.
- Much faster than other methods when using thermal vapor.
- Minimizes risk of over-smoothing.
Cons of vapor smoothing:
- More expensive and complex than other methods.
- Cold vapor method is very slow.
- Requires a vapor containment chamber.
- Strong solvent fumes require ventilation.
Vapor smoothing is unmatched for finish, but also the most involved method. For pro-quality results, the extra effort is well worth it over other methods.
Best Practices for Smoothing 3D Prints
Following some basic print smoothing best practices will help you get great results:
- Print with 100% infill – Smoothing works better on solid prints rather than sparse infill.
- Use a small layer height – Thinner layers blend together better. Aim for 0.1mm or less.
- Handle prints gently before smoothing – Scratches and dents can show after reflowing.
- Apply solvent/heat gradually in thin coats – Better control than over-applying.
- Allow solvents to fully cure before handling – Let the print sit overnight.
- Start smoothing right off the print bed if possible – Smoothing works best on fresh prints.
- Be patient and work slowly – Rushing the process risks over-melting.
- Consider using a clear coat after smoothing – This protects the surface.
Take your time and don’t overdo it on your first prints. Skill comes with practice. Soon you’ll be a pro at transforming rough prints into flawless, glass-like masterpieces!
Give Your 3D Prints a Professional Polish
With a little post-processing, you can make 3D printed objects look store-bought. Start by filling any pores or gaps with filler primer. Sand to prep the surface. Then apply your choice of smoothing technique – solvents, heat, or vapor – for a glossy finish. Finally, spray with clear coat for a lasting shine.
Smoothing is an essential tool for perfecting 3D printed parts. The ability to easily smooth prints opens up new possibilities for highly detailed prints without visible layers. This allows 3D printing to tackle even more professional props, miniatures, cosplay pieces, accessories, and end-use products.
By understanding the various methods for smoothing and their pros and cons, you can choose the right finishing process for your particular prints and applications. Just a bit of smoothing can make a dramatic difference in promoting your 3D printing skills. So try these techniques today to take your prints from rough to impressively refined.
