If you want a 3D printer, the two fundamentally
different options, at least if you want to
spend less than a few grand, are filament
printers, aka FDM or FFF, and resin printers,
aka SLA or MSLA. Last video we covered filament
printers and what you should be looking for
in one of those, today we’re going to go
over when you would want to go for a resin
printer instead and what to consider when
getting one.
This video is brought to you by Elegoo and
their new Saturn resin printer. The Saturn
comes with a new 8.9” monochrome panel that,
compared to the Mars, allows you to print
parts at about three times the size and over
twice as fast thanks to its reduced exposure
times. It also comes with a reinforced Z-axis
and networking built right in. Check it out
at the link below.
When you look at the prints that filament
and resin printers produce, it’s pretty
obvious that they are very different beasts.
A resin printer is capable of producing super
smooth surfaces and fine details that a filament
printer wouldn’t be able to resolve with
its comparatively massive nozzle and large
layer heights. The smallest features a normal
filament printer can produce are at least
about half a millimeter large, if you want
them to look good, it’s more like a full
millimeter. A resin printer, on the other
hand, can work over an order of magnitude
more finely, at just 0.05 millimeters for
the smallest detail it can produce under optimal
conditions. Also, because the layers of the
resin prints are much finer and “melt together”
more, you get a surface finish that looks
more like an injection-moulded plastic part
than a 3D print. And because the layers fuse
together so well, resin prints can actually
be incredibly strong and tough, but that depends
on the exact resin you use.
So the way a resin printer works is that you
start out with the liquid, gooey resin, that
goes into the vat, which has a transparent
bottom, and that goes over an LCD screen that,
instead of lighting up with visible light
like a TV or a computer screen, instead has
a strong UV LED shining through it. So now,
when you have that stackup and turn on the
LED, you get a layer of cured resin on the
very bottom of the VAT wherever that LCD screen
is letting light through and you get no cured
resin in the spots where the screen is masking
off that UV light. Some machines use just
a UV laser and gimbals instead of the UV LED
and the LCD mask, but those machines are usually
a bit more expensive and not the type you’d
start out on.
So, ok, now we have a single, cured, layer
of our part, but really, we want something
a bit more 3D, right? So, in normal use, that
first layer is cured with the build platform
almost touching the bottom of the vat, so
that the resin cures onto the platform, and
then as the build platform moves up, it basically
rips the cured resin from the bottom of the
vat. That clear plastic, that’s a non-stick
film that will allow the cured resin to release
after each layer. So once that’s released,
the build platform moves back down, but now
leaves just a tiny gap, and that’s where
the next layer can form. So on an LCD or often
called “MSLA” printer, the entire layer
is exposed and cured at the same time. So
no matter how large or small your print is,
it’s always going to take the same time
per layer, which means it’s always building
your print up at the same speed vertically,
and as a result, these machines are actually
often faster than filament printers at creating
the same part. Also, if you want to print
several parts at the same time, there’s
no time or quality penalty for that at all
on an MSLA printer.
Now, because resin printers are often relatively
simple machines and don’t have a ton of
moving parts, you can get them for pretty
cheap these days. The components used for
the LCD screen and the electronics driving
all of it are similar to what’s used in
smartphones, so that certainly helps. But
while the machine itself is cheaper, printing
with an SLA printer is more expensive than
using a filament printer. Just as a rough
ballpark, PLA filament costs around 20 to
25 bucks per kilogram, and resin is about
35 to 50 bucks. Now, a filament printer will
almost always hollow out parts and just print
a less dense honeycomb on the inside and then
a millimeter or two of solid material on the
outside. Resin printer don’t do that all
too well, yet. Even if you print your parts
hollow, which the software for many SLA printers
supports these days, you’ll still need a
way for the resin to escape out of the part
and that means adding little holes to your
model for air to get in and resin to get out.
The other option is just printing the part
solid, but of course, when you compare a 100%
dense resin part to the same part done on
a filament printer where you just have a density
of 15% on the inside, well, in that case you’re
using way more resin than filament to make
the same part. It’s most likely going to
be stronger, though.
What also goes into the overall cost and effort
is the assistant materials you’ll use when
handling resin and resin prints. First of
all, nitrile gloves are basically mandatory
whenever there’s a chance you might get
uncured resin on your hands, that means when
refilling resin, handling the vat, removing
a print and when washing and curing the part.
Uncured resin has the potential to slowly
mess up how your immune system reacts to it,
and while getting it on your hands might be
fine for a couple of months or years, once
your body has been sensitized to it, from
there on out, you’re going to have a severe
reaction, from what I hear, potentially even
when you just get a whiff of the resin’s
smell. So please use these resins safely.
That also applies to automotive paints, epoxy
glue and a lot of other things you may not
be thinking about, by the way.
Okay, so you need rubber gloves and other
PPE, then you need a way to clean and cure
your parts. When they come off the printer,
not only are the parts obviously covered in
a layer of liquid, uncured resin, but the
amount of UV light during printing isn’t
enough to completely turn all of the liquid
- and unhealthy - monomers in the resin into
strong, rigid and safe polymers. Either before
or after you’ve got the part removed from
the build plate, you’ll need to get the
layer of uncured resin off, and that is done
by washing the part. Typically, that’s done
with isopropyl alcohol, right now, because
IPA is also a very common, effective and popular
disinfectant, that stuff is kinda prohibitively
expensive and better used for those purposes.
By the time you’re watching this video,
that might have improved, but other alcohols,
like plain old ethanol, or even just soapy
water is supposed to work well, for getting
the resin off, too, but that depends on the
exact resin you use. There are resins out
there that are “water washable”, so you
can rinse those with plain tap water, but
that does absolutely not means that you can
just rinse them off under the tap, in your
sink. Resin should never be washed down the
drain, so whether you’re using IPA or plain
water, you’ll need to do the washing in
a separate container, and once you’ve saturated
your solvent, you’ll either need to find
a way to drop out all the resin that’s dissolved
in there or you need to hold on to it and
at some point dispose of it as hazardous waste.
So look up where you can responsibly drop
off used IPA before you buy some, in my case,
even contaminated solvents are accepted at
some recycling centers.
So after a few minutes, once the part is fully
washed and there’s no liquid resin left
on it, it needs to be fully cured before you
can safely touch it with bare hands and before
it is strong enough to be put into use. Half-cured
parts are pretty soft and crumbly still. The
curing is done with some more UV light, and
the most abundant source of UV light is - the
sun! If you forgot, this is what it usually
looks like. But because the sun not only emits
the less energetic UV-A light that the resin
needs to properly cure, but also the higher-energy
UV-B and UV-C, your part is still going to
cure, but it might end up getting a bit of
a suntan along the way, turning brown, and
becoming more brittle than if it was cured
properly. Supposedly, this is not due to overexposure,
but because the UV-C light actually breaks
down the monomers instead of curing them.
So ideally, you’d get a curing station that
just has some more UV LEDs in there or, if
you don’t mind pointing a UV flashlight
at your part for a few minutes, you can also
use that and cure your parts to taste.
The post-processing is definitely the largest
chunk of effort that you will need to put
into getting resin prints done, and if you
think you’ll be doing a lot of resin printing,
you should factor in getting or building some
sort of a cleaning and curing setup from the
start.
So a resin printer uses fewer moving components
than a filament printer, and typically, when
you think about how machines wear down, it’s
because bearings and other stressed components
start to fail. While I wouldn’t worry much
about the few moving parts in a resin printer,
there are some spots that you should be paying
attention to. First, the FEP film at the bottom
of the VAT is considered a consumable - with
thousands of times per print where the freshly
cured layer of resin is ripped off that film,
that’s not really a surprise. Sometimes,
you might also find bits of previous prints
stuck to the film when things didn’t go
perfectly smoothly and those can be a bit
tricky to remove without damaging the film.On
most vats, this film is replaceable, though.
The other components that have a limited lifespan
are the UV LED and the LCD masking screen.
On newer printers, the design and cooling
of the UV LED has much improved, so spontaneous
failure shouldn’t be much on an issue anymore,
but like any LED, these will slowly get dimmer
over time. But for the LCD screen that is
then responsible for blocking off the UV light
where you don’t need it, that part is still
something that isn’t optimized for this
application yet - at least on most printers,
it’s a straight-up phone or a tablet screen,
and these aren’t made to work to with the
sheer amount of light that resin printers
need to work with. So when picking a printer,
take a look at what usable life the manufacturer
warrants on the screen and also what it costs
to replace it when it’s fails. Some newer
machines use LCD screens that are specifically
modified to work better for resin printers,
for example by turning them into a monochromatic
screen, which leaves out the color filter
that would otherwise block ⅔ of the usable
light, and that will make printing faster
and therefore use less of the screen’s limited
lifespan per print, but as of right now, there’s
too little experience with them to say if
these newer screen will actually give you
a longer lifespan as well.
But the thing is, when you look at the results
you get from a resin printer, that amount
of detail and surface finish is incredibly
impressive, and there’s not real other way
to get that. Yeah, you can print at super-fine
layer heights with a filament printer, too,
but you still can’t compare the results
from that with a real, high-detail resin print.
Let’s recap! Resin printers work on a much
finer detail scale than filament printers
and instead of plastic filament that gets
melted down, they use a liquid monomer resin
that turns into a rigid polymer when it’s
exposed with UV light. Most resin printers
these days use an LCD screen to block off
the light anywhere the part should not get
exposed, some more expensive machines use
a UV laser. Resin prints are often printed
solid, but you can also hollow them out to
save material. Honeycomb structures on the
inside like on filament printers is something
that’s still being figured out.
Resins themselves are a bit more expensive
than filaments and require special attention
when it comes to handling them. At least wear
disposable nitrile gloves, as well as any
other protective equipment that may be necessary
to keep you from coming in contact with uncured
resin. But once the parts are fully cured,
they are perfectly safe to handle.
You’ll also need some extra equipment for
post-processing fresh resin prints, specifically
a way to wash and then evenly cure them. While
resin printers are pretty foolproof mechanically,
the thin FEP film between the LCD masking
screen and the resin, as well as that screen
itself and the UV LED are parts that can deteriorate
and eventually fail. But the results you get
from these printers are worth it because there’s
just no other way to achieve such a high amount
of detail and uniform strength.
So that’s it for this one, in the next video,
we’ll get back to filament printers and
look at what parts they are made of and what
sort of care and maintenance they need, until
then, thank you for watching, make sure to
get subscribed, keep on making, and I’ll
see you later.
