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 2.5×100 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,
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and I’ll see you in the next one.