FIGURE 61: The resin printing process (shown using a DLP light source). Infographic by HoneyPoint3D™
The previous chapter discussed FDM 3D printers, which represent about 90% of the consumer market. The
other 10% belongs to a special class of 3D printers called resin printers. You might also see the term “SLA”,
masked SLA (mSLA), or DLP (digital light processing). SLA is an acronym for “stereolithographic appa-
ratus,” which basically means “gizmo that writes with light.” These 3D printers create very detailed prints
with smooth surfaces, but are more difficult to use, so it is important to know their benefits and drawbacks
before you buy your first liter of resin.
HOW IT WORKS
These 3D printers do not use filament; instead, they use a liquid resin (polymer) that hardens or “cures”
when exposed to ultraviolet light. The 3D prints from resin printers are still made layer by layer, but are
created in a slightly different way.
The basic printing process for a resin printer is:
1. A vat of liquid resin sits in the 3D printer. The bottom side of that vat is transparent, allowing light to
2. A build plate gets submerged downwards from the top to the bottom of the vat, until there is a very
small layer of resin between the bottom of the vat and the build plate.
3. A controlled light, pointing upward from the bottom of the 3D printer, hits the build plate in a specific
pattern, hardening the resin in that specific pattern.
4. The build plate then moves slightly upward, pulling the newly cured layer along with it.
5. The light shines again in a slightly different pattern from the previous layer, and then cures to the
layer that was created before it.
6. The process repeats until the object is complete.
For a graphical representation of the process, see Figure 6-1.
The goal of this chapter is to show you the differences between FDM and SLA printers, as well as point out
some unique considerations when running an SLA printer.
HERE ARE SOME NOTABLE DIFFERENCES BETWEEN RUNNING AN SLA PRINTER VERSUS AN FDM PRINTER:
• The resin is ideally kept at around 80 degrees Fahrenheit in order for the viscosity of the resin not
be affected. A thicker/colder resin will need more time to flow back under the build plate between
• The resin has a noticeable odor…a kind of sweet, but strong chemical smell that may bother some
• The resin printer must be kept away from windows because any extra sunlight might cure some of
the resin inadvertently.
• You must wear gloves when handling the resin and the newly created 3D print, as well as, for
cleaning the printer to avoid getting resin on your hands. This means, essentially, wearing gloves
every time you physically interact with the printer.
• Kids and pets should be kept away from the 3D printer and resin. The resin should be considered
as dangerous as household bleach.
• After the resin print is finished, it will need to be rinsed by hand in isopropyl alcohol.
• Once the resin print is washed off, it is a good idea to place the print in direct sunlight or in a UV
curing box for 10 minutes to finish curing the outer layers.
• After the printing is finished, you will need to remove tiny cured particles of resin that may have
appeared in the vat and could interfere with future prints. You should pour the leftover resin
through a commonly available paint filter or into another container and label that container “used
resin” (not mixing it back in with the unused resin). Resin keeps for a long time, but it is recom-
mended to use up the resin that has already been exposed to light before opening a brand new
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