Stereolithography: Sorting Out Surface Finishes

There are a number of factors—resolution, tolerance, material selection, surface finish—to consider when designing for the industrial 3D printing process of stereolithography (SL). For our latest tip, we’ll discuss the four stereolithography finishing options available at Proto Labs, and when it makes sense to use each.


Stereolithography (SL) technology uses a build platform that requires support structures for all features so they don’t float away or collapse during the build process. These support structures are removed after the build is complete, but they do leave visible markings on the part.

stereolithography proto labs

3D-printed parts are moved from the SL chamber after a build finishes. Supports are then removed, parts are UV cured, and a selected finish is applied.

In an unfinished state, after the support structures are removed, dots or nibs are noticeable where structures were attached to the part surfaces. So, when would leaving a part unfinished make the most sense?

  • When a clear part is desired with no custom finishing
  • If you have your own finishing capabilities, or have another shop that can perform post-build finishing
  • To achieve the best accuracy possible


A natural finish provides a surface finish that absent of dots or nibs, which leaves a more desirable cosmetic appearance. The surface is not as clear on the down-facing surfaces that had supporting structures, but the top surface would remain clear. When should you use a natural finish?

  • On small or delicate features that may be destroyed by additional finishing such as grit blasting
  • On clear parts where down-facing surfaces are not a cosmetic concern

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DESIGN TIP: Choosing Industrial 3D Printing for Production Parts

Using 3D printing for fully functional end-use metal and plastic parts is becoming increasingly common in rapid manufacturing with industrial-grade processes like direct metal laser sintering (DMLS) and selective laser sintering (SLS).

Industrial-grade 3D printing is well suited to produce organic shapes, like this nylon turbine (left) and end-use production parts such as this titanium drill component (right).

With an expanding material selection and improving material properties, designers and engineers have another good option for small quantities of production parts.

Accordingly, our monthly design tip covers this emerging trend.

This month’s tip discusses:

  • Choosing the best 3D printing process for your application
  • Selecting the right thermoplastic and metal materials
  • Designing part geometry for 3D printing
  • Using SL, SLS, and DMLS for end-use production parts


Q&A: Eric Utley Discusses the Advantages of Stereolithography

Eric Utley, application specialist at Proto Labs.

We’ve been 3D printing for a while now, and our facility in Raleigh, North Carolina is packed with 3D printing specialists. For this installment of our Q&A, we spoke with one of those experts, Eric Utley, application specialist, for a chat about stereolithography and why product designers and engineers need it for prototyping.

To start off, can you give a quick overview of the stereolithography (SL) process?
Stereolithography uses UV light shot from a laser to cure a liquid thermoset resin called a photopolymer. In fact, even though 3D printing is often thought of as a new technology, SL has been around since the 1980s. But there’s a reason it has stuck around for so long — it has some key features that product designers need for prototypes.

What are some of those key features unique to SL?
I’d say the most important feature is that it creates a very high-resolution part with excellent surface finishes.

It can handle micro-sized features so it’s most suitable for parts that have a high level of detail. Most SL parts will have a nice, smooth finish and, although it’s typically used for prototyping, it leaves you with the feel of a final part — and looks go along way when sharing your new product design.

Another important benefit of SL is that it’s our most flexible process in terms of geometry it can handle, which gives designers a lot of freedom to work with.

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TIPS WITH TONY: Can 3D-Printed Parts Take the Heat?

Here’s a question that’s often asked: How do materials used in 3D printing compare to injection-molded thermoplastics when the temperature rises? To answer that, I’ll briefly dissect the materials used in stereolithography (SL) and selective laser sintering (SLS) processes as these are commonly compared to injection molding.

SL involves a thermoset resin that is solidified by an ultraviolet laser, followed by a UV post-curing process to completely solidify the resin. As far as material properties, the big takeaway is that SL parts are built from thermoplastic-like resins, so they do break down over time in direct UV light.

SL uses materials that mimic ABS, polypropylene and glass-filled polycarbonate, and they offer an array of material properties still exist. But today we’re concerned with the thermal properties of the materials that are best suited to handle the heat — 3D Systems Acura 5530 and DSM Somos NanoTool. Both are offered in post-cured states and there’s an additional process for thermal post-curing that increases the operating temperatures.

The chart shows optimal heat deflections for SL materials. The other materials offered in SL have a much lower heat deflection ranging from 120˚F to 177˚F.


UV Post-Cure

UV Post-Cure +
Thermal Post-Cure

3D Systems
Accura 5530

85˚C (185˚F)

250˚C (482˚F)

DSM Somos NanoTool

225˚C (437˚F)

263˚C (506˚F)

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Why Stereolithography is Built for Prototyping

Stereolithography (SL) is an established additive manufacturing process that can quickly and accurately create complex prototypes. Parts are built by curing paper-thin layers of liquid thermoset resin with an ultraviolet (UV) laser that draws on the surface of a resin to turn it from a liquid to solid layer. As each layer is completed, fresh, uncured resin is swept over the preceding layer and the process repeated until the part is finished.

SL offers a range of plastic-like materials to choose from with several types of polypropylene, ABS and glass-filled polycarbonate available. Normal, high and micro resolutions are achievable at Proto Labs, meaning very fine details and cosmetic surfaces are possible. As a result, minimal “stair stepping” is seen compared to printed parts such as fused deposition modeling (FDM).

SL parts can also be built to a max size of 29 in. by 25 in. by 21 in., giving it the edge over other additive processes like selective laser sintering (SLS).

Our latest design tip looks at these and other manufacturing considerations for the stereolithography process.