Today, we’re going to cover the mechanics - the frame, linear guides and motion system.
There are a few choices you can make here to make things easier, but I think making
as much as possible yourself is the way to go if you want to stay true to the core ideas
of the build. I mean, this is the fun part, after all, right?
So let’s start with the frame itself - as you can see, I already made a near-perfect
copy of the original one. It even has the PRUSA name up top here, so you know it’s
the real deal. This one is cut from 18mm or ¾ inch OSB board, it’s not the greates
material ever, but it’s certainly stronger and stiffer than MDF, particle board or even
thin acrylic. To cut it out, I started with the original frame design files, overlaid
an Escher grid as an alignment pattern and then printed it with the “Poster” function
in Adobe Acrobat, I think the regular Adobe reader has that functionality, too. The frame
really isn’t that large, so you’re only going to use four A4 or Letter-sized sheets
of paper. I aligned them, stuck them together with tape and then glued them onto the sheet.
Glue stick works much better for this than wood glue, by the way. Then I started by drilling
the holes in the frame, these do need to be fairly accurate, so take your time here, and
also drilled the seats for the threaded rod frame with a 10mm bit to get them perfectly
round. The rest was just a bit of cutting everything out with the circular saw and jigsaw,
the geometry of the frame isn’t super crucial, so don’t worry if your frame comes out looking
as shoddy as mine. You can use whatever tools you have for this, whether it’s only a jigsaw,
bandsaw, scrollsaw or even a fretsaw. For the jigsaw, I can definitely recommend one
of these thinner curve blades for the smaller details of the frame, it just makes getting
in and out of the corners much easier. To get the template off, I gave it a quick pass
with the belt sander and then went back and cleaned of the details with a file and rounded
over the edges with some sandpaper. Now, you could make the bed frame from the
same material, but I went with a 10mm aka ⅜ inch MDF sheet instead here, since the
bed sub-frame needs to be a bit lighter and the finer details don’t lend themselves
to the coarse structure of the OSB material. So with a fresh printout of the template,
again, you want to start out with the holes. You don’t have to be as precise as with
the main frame here. But let’s look at the way the bearings are mounted in here. The
two outer holes are only through-holes for zipties, and the elongated cutout in the center
is actually what aligns the bearing. These frames are made to be CNC cut, which would
of course align the bearings perfectly, but when making these by hand, I’d actually
recommend starting with a 10mm drill bit in the ends of the slots and then cutting the
hole slightly tapered, so that it’s slimmer in center, which will allow the bearing to
self-align to the direction of the smooth rods, otherwise they might end up binding
if they are just a tiny bit off. Remember, you can always come back with a file and adjust
the shape to get them perfectly lined up. I also started with a 10mm drill bit in the
corners of these larger cutouts and then cut between the holes to give them a rounded shape
in the corners, which should make the part harder to break.
And again, these don’t need to be Matthias Wandel - level parts, how the edges looks
doesn’t impact how the machine will perform in the slightest bit, but of course, you can
tidy them up and make everything look neat if you want.
So the holes here are sized to have M3 screws directly screwed into them without being tapped
or anything. A 2.7mm drill bit worked well for me with OSB, but the screw lengths I’ve
got in the bill of materials are long enough to stick out the back and be fastened with
a washer and a nut there. Plus, If you mess up the hole, you can always just make it a
bit bigger to align things properly. Of course, you could also just buy a full
frame kit, but those cost around 40 bucks, while the materials I used to make one myself
were about 4 bucks if you’d actually buy them, in my case, it was literally scraps
I had sitting around. Alternatively, you could route the frame out
on a CNC router, too, the dxf files for that are on Prusa’s github pages.
Talking of fasteners, again, the full list of parts I’m going to use is on Toms3d.org/dolly,
but the ones worth talking about are the following: Threaded rods. There are three sizes here,
M5, M8 and M10. The M5 will be used for the Z-axis, so that one is sorta non-replaceable,
but if metric threaded rods are hard to get or expensive in your country, you can substitute
5/16th and 3/8th threaded rod for the M8 and M10 ones. One meter of each is plenty, but
I did order a second M5 rod just to have a backup if one of them should come bent. Plus,
they are super cheap here anyways. Blank steel ones might be even cheaper than galvanized
ones, but they will rust. Stainless is harder to cut and more expensive. Also, if you have
the option of different strength grades, pick the cheapest one. We’re not going to get
anywhere close to their yield strength with the MK2 build.
I’ve also tried to eliminate as many different variants of the screws as possible. While
having seven different lengths of M3 cap-head screws won’t matter much when you’re buying
tens of thousands of each size, us little people usually only buy a handful. And the
interesting thing is, the smaller the lots you buy are, the more costs for just packaging
stuff is going to factor in. For example, 2000 stainless M3 washers don’t even cost
twice as much as just 200. But, if you’re interested in making things, which I would
assume since, right now, you are watching a video about making a 3D printer from scratch,
getting those bigger packs will leave you plenty of spares for projects down the road.
I paid about 50€ for a full set of fasteners - screws, nuts, washers, and threaded rods,
but it’s enough for at least five printers, so I guess the effective value of all the
hardware we need is about 10 bucks or so. If you have a decent hardware store nearby
- and I’m not talking about the home depot or similar - you might be able to buy the
exact amount of fasteners you need. A few notes on the parts in here: Locknuts.
These have a small nylon section on the end that keeps them from coming loose, but they
are expensive, so alternatively, you can instead use two nuts and jam them against each other
- those are never going to come loose - or just use a regular nut with liquid threadlock,
or even superglue if you have to. Then, I’ve ordered all the M3 and M10 washers
that will seat against the wooden frame as larger fender washers, these are about twice
as large as regular ones. And lastly, the Original MK2 uses some M5
hardware, but only in the extruder to hold the bearing. We do need a pair of M5 nuts
for the Z-axis, but I’ve redesigned the extruder idler to not need any 5mm hardware
at all, the bearing pin is printed and the side guides for the bearing are integrated
into the idler itself. Speaking of modified parts, I’ve also been
working on making the printed parts fit the cheaper components used in this build. Particularly,
the X and Y motor mounts to fit the larger endstops, the Y-corners to fit standard length
smooth rods and some new Z-axis nut holders. Also, spacers for the Arduino Mega + RAMPS
that will be the brains of this operation. The rest of the parts are the standard MK2
one, and the ones I modified aren’t that far off from the originals. If you already
have a 3D printer, well, of, course, print them, but alternatively, you could either
have them printed at a local FabLab and learn a bit about the machines in the process, or
try a service like 3DHubs. The original MK2 uses ABS for everything but the electronics
cover and power supply mount but those parts are a copolyester. We’ll still need to figure
out a way to brace the power supply in here, but I’ve got a few ideas there. Realistically,
I think most parts would be fine from PETG/CPE/copolyesters, whatever you want to call them, but I would
print the extruder parts and X-axis carriage from ABS, HIPS or ASA just to get that extra
bit of temperature resistance. So far, I’ve printed all the parts from rigid.ink ABS,
and most parts actually don’t care too much about print quality, so if they’re printed
coarsely or warped a bit, the final printer we build with them is still going to work
just fine. Ok, what else? Well, linear motion. And that
is guides and belts, essentially. The standard set of smooth rods for an i3 is two each of
320, 350 and 370mm 8mm rod, however the MK2 uses 320, 330 and 370, which is really hard
to buy. You could ask a seller to make them to that size, or just go with a standard set
and use two of the modified printed parts to have the rear of the Y-axis ones overhang.
Definitely go with hardened, and ideally chromes ones, you might be able to find, like stainless
rods cheaper, but they are just going to wear in super quickly and leave you with an extremely
sloppy axis in no time. Plus, at 27 bucks, you do get a set of rods you’ll be able
to use even if you completely rebuild and upgrade this thing.
For bearings, I’ve found that there is little to no difference between the super cheap and
slightly more expensive ones, so I’d recommend just getting the cheapest ones and picking
up an extra pair so that you can choose the best ones. You need 10 pieces for the printer,
so a dozen LM8UU are less than 6 bucks. What you also need are belts and pelt accessories
- since the printer uses open-loop belts that get clamped at the ends, you can just buy
a 2m length of belt as a set with the 16 tooth pulleys for X and Y, cut the belt to length
as needed and spend less than $2.50 for the whole thing. But make sure you get the 16
tooth and not the 20 tooth ones. As idler bearings for the belt, there are ready-made
ones with a 3mm bore available, whether you get the ones with or without the belt teeth
doesn’t matter too much. Either type is about a $1.50 per piece, I’d personally
choose the ones with the belt teeth. And you’re going to need one more bearing,
yeah, just a single one of the 625 type, and you can’t really buy just one of these,
but at $1.50 for 10, it’s not that big of a deal. If you’re buying fasteners from
a proper hardware store, they might also have these bearings.
To make the hardware complete, you’ll need like a 100-pack of the standard 2.5x100 mm
zip ties and two more essential parts: Z-axis coupler couplers and motors. Now, I realize
the Z-axis I’m suggesting here is much closer to the Prusa i3 MK1, but that doesn’t mean
it’s not going to work as well. The MK1 was already an excellent machine and printed
absolutely beautifully, but of course, the Z-axis was a bit slower than the MK2’s.
It also used what looks like shrinkwrap as Z-axis couplers. And I’m actually going
to suggest doing something similar by using a bit of aquarium or watercooling hose with
a 5mm inner diameter to couple the motor shaft to the M5 threaded rod, secured by a bunch
of zip ties. This works extremely well, probably even better than real couplers, but of course,
you can use those, too, and they’re not that epensive at around 80ct per piece. The
choice is up to you, I definitely like the PVC tubing solution a lot, but either one
can work. And lastly, motors, for these, thanks to 3D
printing being so popular these days, you can’t really go wrong by buying whatever
set of 5 NEMA17 motors you find on the cheap. These are mostly going to be very similar
types, around 40mm long with a torque of about 40Ncm. Totally ok, no high-end requirements
here, and whether you get them from an importer or directly from China, a set is going to
cost about $42. Yes, that is the single most expensive component group yet, but then again,
these are heavy, and heavy things are expensive to ship around. But then again, these are
also parts that you can use for any 3D printer or other machines, but really, I don’t see
why you’d ever want to take this thing apart again.
Uhm, yeah. Well, so next up, I guess it’s time to build this thing. As always, that
is going to happen in a livestream, but I’ll also compress the build notes into a regular
video of the series so that you won’t have to sit through a 15-hour video just to get
the rough idea. The build is going to go by the original manual from Prusa, but again,
the next video will highlight the differences where things aren’t quite as plug-and-play
or just differ in what parts to use. For now, the updated bill of materials, the
modified 3D printed parts and the template for the frame are available on toms3d.org/dolly,
and once everything is built and tested and works, I think I’ll also upload the entire
project pack to YouMagine. And that’s it for today, if this video helped
you out and maybe you’r even already working on building your own, give the video a thumbs
up, if not, leave a comment on how I can improve, constructive criticism is always appreciated.
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And that’s it for today, thanks for watching, and I’ll see you in the next one.