UNDERSTANDING
RESIN PRINTERS
6
CHAPTER
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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
shine through.
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
layers.
• The resin has a noticeable odor…a kind of sweet, but strong chemical smell that may bother some
people.
• 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
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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
shine through.
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
layers.
• The resin has a noticeable odor…a kind of sweet, but strong chemical smell that may bother some
people.
• 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
resin bottle.
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FIGURE 62: Eiffel Tower model printed on an SLA printer (3D
model credit: Pranav Panchal)
FIGURE 63: lose-up photo of Eiffel Tower with each individual
railing measuring just .2 mm
• Unless you plan on storing the resin in
the vat (which may get dust in it or spill if
knocked over), you should wipe the resin vat
clean with a small non-abrasive wiping tool.
• You will need to replace the vat over time.
The vat that holds the resin is considered a
consumable, with a typical lifespan of about
3–4 liters of resin. Vats range in price but
average around $50–$80 each.
• mSLA printers (described below) also have
a consumable LCD screen which blocks the
light to create the patterns to be printed.
Over time, the heat from the lamps degrades the screen to be the point of needing a $100-$600
replacement (depending on LCD/printer size). The lifespan on our own $500 resin printer is about
400 hours of screen-on time, resulting in about a 6 month replacement cycle.
As you can see, there are a lot of considerations you need to take into account with a resin printer. If you are
willing to conduct the process, however, you can enjoy truly exceptional prints, as shown in Figure 6-2 and
Figure 6-3.
Third-Party Resins
While most SLA printer manufacturers allow the
use of third-party resin, other manufacturers
state in their terms and conditions that their
printer warranty will be void if third-party resin
is used. We recommend you read the terms
and conditions of any printer you want to buy
thoroughly to make sure you can use third-party
resins.
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• Unless you plan on storing the resin in
the vat (which may get dust in it or spill if
knocked over), you should wipe the resin vat
clean with a small non-abrasive wiping tool.
• You will need to replace the vat over time.
The vat that holds the resin is considered a
consumable, with a typical lifespan of about
3–4 liters of resin. Vats range in price but
average around $50–$80 each.
• mSLA printers (described below) also have
a consumable LCD screen which blocks the
light to create the patterns to be printed.
Over time, the heat from the lamps degrades the screen to be the point of needing a $100-$600
replacement (depending on LCD/printer size). The lifespan on our own $500 resin printer is about
400 hours of screen-on time, resulting in about a 6 month replacement cycle.
As you can see, there are a lot of considerations you need to take into account with a resin printer. If you are
willing to conduct the process, however, you can enjoy truly exceptional prints, as shown in Figure 6-2 and
Figure 6-3.
COST OF MATERIALS
Resins are also relatively more expensive than FDM filaments,
though they are slowly coming down in price. The least expen-
sive resin can go for $25 per liter (1000 mL) and the most
expensive general-purpose resin can go for $100 per liter (these
are usually for jewelry burnout /casting processes).
In general, the price of 3D printing with a $30 liter of resin is about
on par with printing in PLA on an FDM printer when measured per
cubic centimeter. The more expensive resins are similar to printing
with specialty FDM filaments (like impact modified PLA, or flexible
filaments). A full description of the costs associated with 3D printing
in resin can be found in Chapter 9.
TYPES OF RESINS
Because of the way resin is formulated, there is less choice in material properties for the SLA printers than
what you will find in FDM printers.
THE MOST COMMON TYPES OF RESINS FALL INTO THESE FOUR CATEGORIES:
• Normal/general-use
• Hard/durable
• Flexible
• Castable
There are almost always trade-offs and benefits when moving from one type of resin to another. For
example, resins that are made for strength and durability cannot print in fine details like normal, gener-
al-use resins. But, those more durable resins can take more physical stress than the general-use resins
Some 3D printer manufacturers also manufacture their own resin, and they (usually) strongly suggest that
only their specific brand of resin is to be used in their printers.
HERE IS A LIST OF POPULAR RESIN VENDORS.
• Formlabs Resin
• MadeSolid Resin
• B9 Resins
• MakerJuice Resin
• Spot-A Materials
• Elegoo
• SirayaTech
How Castable Resins
Are Used
Most castable resins need to go through a
burn-out process. The resin print is placed
in an investment-casting material (plaster)
that is hardened, and then the mold is
placed in a kiln to burn out the resin inside.
This leaves a hollow cavity, and the molten
metal used for casting is then poured into
that. Castable resins are predominantly
used in jewelry design and production.
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