This is the beautiful planetary gearbox of
the Prusa MK4 3D printer and it’s a pity that you usually don’t see it because it’s
covered by a lid. So let’s try to fix that today and make see-through covers using three
different methods: FDM 3D printing using transparent filament, resin printing using clear resin
and CNC machining a cover from acrylic. Which method is the easiest to use and which gives
us the clearest result? Let’s find out more. Guten Tag everybody, I’m Stefan and welcome
to CNC Kitchen. This video is sponsored by VOXEL PLA. Get
1 kg of their reliable Pro PLA for only $16.99. Check them out at voxelPLA.com. The planetary gearbox of the Prusa MK4 is
part of the extrusion system. It reduces the higher RPM extruder stepper motor 10:1 to
precisely feed the filament into the hotend where it melts and allows us to create these
beautiful 3D prints with it. Watching a planetary gearbox with the sun gear in the middle and
the planets spinning around it is something that’s not only mesmerizing for engineering
enthusiasts. Yet Prusa, unfortunately, hides it and since I grew up with transparent Gameboys
and Consoles, I wanted to give my MK4 a special see-through cover so that we can watch the
internals working. So the first obvious choice was printing it
out of transparent filament. Yet if you ever printed with this type of material, you’ll
know that these parts will be translucent, so they will let light through but are not
transparent as a piece of glass. Though there is a method using an FDM 3D printer to make
a real transparent part that also has the advantage that these parts show almost perfect
layer adhesion because the layers bond so well together. I’ve made a full video on
that which I highly recommend you to check out later! I downloaded the model of the latest
cover from Printables yet noticed that this model has a revision number on the inside
which would be distracting our view onto the gears. I could have used a simple modifier
geometry within PrusaSlicer to get rid of it yet decided to do it properly and remove
it in the CAD model. A bit contrary to their Open Source and Open Hardware approach, Prusa
doesn’t currently provide any CAD files of their MK4, so I had no other option than
reverse engineering the cover. I simply loaded the stl file into Fusion360 and carefully
sketched out the part, making sure that I got all of the dimensions right until I ended
up with an almost perfect parametric CAD model for me to play around with and print. I uploaded
the CAD file on Printables if you want to play around with it! I exported this model
again into PrusaSlicer and tried to reproduce the magic print settings I came up with in
the last video. If you want to print transparent parts, there are some main points you need
to look out for. Use transparent and dry PETG. Print at low layer heights. I used 0.1 mm
in my case. Print slowly and rather on the hot side and slightly increase flow. And I
think one of the most important points is to use 100% Aligned Rectillinear infill so
the infill lines are all going in the same direction, leaving you with a part, that turns
out pretty transparent. Yet I wanted to know what the best method
for making a transparent part is, so before we take a look at the final result that I
printed with filament, let’s put one of my new toys into action. This is CARVERA,
a desktop CNC that the kind folks over at Makera sent over. The CARVERA uses ball screws
and super beefy linear rails, yet the feature that intrigued me is that it has a tool changer
that can hold up to 6 different bits. I think where this machine really shines is PCB prototyping
using the included laser because the 200 W spindle might be a bit underpowered for heavy
machining, but if you don’t push it too hard it should be able to make some nice-looking
parts out of wood, plastics and even aluminum! I’ll be machining some acrylic with it!
Good for us that we just reverse-engineered a CAD model for the cover because this is
what we need to generate the GCode to run the CNC. Generating GCode for such a machine
is a bit more involved than setting up a 3D print job, because we’ll need to decide
which tool to use and which is the suitable operation for the feature we want to create.
After modifying some design features I wouldn’t be able to machine I switched to the manufacturing
environment in Fusion360. This is the CAM workspace which stands for computer-aided
manufacturing. This might be intimidating for some but trust me, it’s a really interesting
process and if you’re using Fusion360 yourself, you can download my file to play around with
it yourself. First, I defined the stock material I wanted to use, which was an 8 mm clear acrylic
sheet I had lying around. Using a single flute, ⅛” endmill I defined the first operation
which is face milling that removes material so that we get the desired thickness of the
cover. The next two operations get rid of the bulk of the material on the inside of
the cover, yet in order to get a clean finish of the walls, I also added contour paths around
all of the internal details. The four holes are bored with a helical toolpath so the 3.175
mm endmill is able to drill a 3.3 mm big hole. Next comes the cool part of the CARVERA and
this is using the toolchanger. All the operations we did so far used the single flute endmill,
yet in order to add some chamfers we need to switch tools and use a 45° chamfer bit.
This tool has a dedicated tool number that corresponds to the tool positions in the router,
so the machine knows where to pick up the new endmill. With this bit I created a toolpath
for some bigger chamfers and, because I can, deburred some of the edges. For the final
operation, I switch back to the regular endmill to cut out the part, yet leaving some taps
so that it doesn’t come loose uncontrollably. Though there is one last feature that still
needs to be machined and this is the bolt head pockets on the other side. Obviously,
we can’t machine that from the first side, so we need to flip the part around and do
a second setup. Here, the four pockets are simply machined with a bore operation.
Once that was all done, I saved the two GCode files that look very similar to a 3D printing
GCode file and went into the control software of the CARVERA, where I uploaded them to the
machine. I fixed the acrylic sheet with some clamps on the table and started machining.
First, the CARVERA picks up the wireless touch probe, measures its length, and then probes
the height of the workpiece. It then drops the probe, picks up the tool measures its
length, and goes to work. Even though it’s a bit underpowered and the spindle might not
be the stiffest, it was able to chew through the material really nicely. The integrated
vacuum helps to remove some of the chips, yet I still regularly just opened the cover
and manually vacuumed the plastic bits away. The first side took 10 minutes to complete,
after which I broke the taps and fixed the cover in place for the second operation. The
CARVERA measured again the part height and within just 30 s finished the four bolt head
pockets. The result looked really nice with quite accurate dimensions. The only problem
I had was that the machined surfaces were milky and not as transparent as the initial
surface. Yet there is an easy way to fix that! But before that, let’s talk about my third
and last method - printing the cover out of clear resin on my Prusa SL1 Speed. I still
had a bottle of Elegoo clear resin from a previous project around, which should give
us an idea of how clear of a print we can get. PrusaSlicer would actually suggest printing
the part at an angle so that we only need supports at the edges of the part and get
really clean surfaces. Yet if we take a very close look at a resin print, we can see that
the printing method, so exposing resin layer after resin layer using an LCD, produces a
Minecraft-like voxel structure that diffracts light and makes it look milky. That’s why
I decided to print it flat on the platform with supports under it, so we barely get angled
surfaces. This print only took a bit more than 20 minutes to finish and after cleaning
it in isopropyl alcohol and curing it, I was left with another really nice part. Removing
the supports of course left a ton of scars on the bottom, yet on such a flat part they
are easily removed with a bit of wet sanding. I only got down to 600 grid which also left
me with a slightly cloudy finish, kind of similar to the two other methods. So let’s
fix that! On the resin part I simply used a bit of plastic
polish and after just a bit of scrubbing left me with a very nice part. The only issue I
was directly able to see was that the resin yellowed, which is a common problem when UV
resins cure. There seem to be some really clear resins around, yet I never tried them.
If you have a recommendation, then let me know!
The cover that we printed with the clear PETG resin also looked a bit cloudy due to the
texture of the print platform. We could also go through the hassle of sanding and polishing
that layer. Yet, what works almost just as well is adding a drop of oil onto the surface
which evens out the roughness and makes the part look way nicer. Unfortunately, the cover
still didn’t turn out completely clear and we’re still able to see some streaks in
the direction of the infill. There is still potential for tuning that process even more
by adjusting temperatures, flow and speed, yet I’m still impressed to see how transparent
we’re able to print if we simply adjust some critical settings. Let’s finally finish
the cover we machined from acrylic. This looked the cleanest, yet the machined surfaces are
still a bit milky. Flat and exposed surfaces would be polishable, yet doing that on the
complex interior would be a hassle. This is why I used the same oil trick as before and
after coating the surface with a thin film, the result looked seriously beautiful! The final thing remaining is to install it
on the MK4. So I carefully unscrewed and removed the cover. Prusa strongly advises using the
alignment tool not to damage the planetary gearbox, so just keep that in mind. I then
removed the small bearing ring from the stock cover and pressed it into the clear cover.
It’s a bit unfortunate that this black part covers some of the gearbox, but it still leaves
enough room to now finally see all of the gears in action. The big question now is, which of the transparent
covers do you prefer? Is it the one you can print on any FDM printer yourself with just
some magic settings? Would you print yours in clear resin, because it’s fast and easy
if you have a resin printer? Or do you think the CNC-machined one is worth the hassle?
Let me know in the comments and if you enjoyed this video make sure to leave a like and subscribe! I personally prefer the machined cover and
not only because it was a pleasure to make. A CNCd part simply has a certain aesthetic
that I really dig. And this is now the perfect opportunity to load some filament from VOXELPLAs
new colors that they just released and see the MK4 finally print at über speeds with
the Input Shaping Alpha firmware. I’ve been printing quite a bit of VOXELPLA over the
last months and even though they might not have the most fancy colors their PRO PLA that
sells for only $16.99 a roll with free shipping in the US if you’re buying three spools
or more is just a great general purpose printing filament. VOXELPLA developed their material
for their own print farm, where they run 150 production machines, so you can be sure that
you’ll get a reliable material for your own projects or your business. VOXELPLA has
a ton of different colors, is in stock, and is ready to ship the same day! It can be used
on all of your FDM printers and even works great in your BambuLab AMS. So if you live
in the US and want to restock your filament, visit them at voxelpla.com where you can also
check out their bulk discounts. Thanks to VOXELPLA for sponsoring this video!
Thanks for watching, everyone! I hope you found this video interesting! If you want
to support my work, consider becoming a Patron or YouTube member. Also check out the other
videos in my library! I hope to see you in the next one! Auf wiedersehen and goodbye!
