Building the cheapest possible Prusa i3 MK2 clone: [02] Frame and motion!
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Building the cheapest possible Prusa i3 MK2 clone: [02] Frame and motion!

October 11, 2019

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, 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 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, 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. Also do consider subscribing to the channel,
and click that bell or you YouTube might not notify you when the build stream goes live
and the next videos get released. If you’re going to be shopping on Amazon
or Aliexpress in this case, check out the affiliate links from the video description
or head over to Patreon to support the channel directly and get access to monthly Q&A hangouts
and more. And that’s it for today, thanks for watching,
and I’ll see you in the next one.

Only registered users can comment.

  1. If I was going to make the frame out of metal, how thick would the aluminium need to be? I can either CNC it myself or get it professionally water jet cut if too thick

  2. hey Tom, great series. my son and I are gathering parts to follow along with the build.

    Question about the stepper motors? Can I use steppers pulled from other electronics? specifically copy machines. I'm a copy machine technician and can pull up to five of the 1.7in motors and a 2in stepper out of a single Japanese recycled copy machine. Most are the same looking but some are slightly different looking tho still 1.7. can I mix different powers or torques together?

    Thanks sooo much, can't wait for the build stream

  3. @Thomas Sanladerer I was expecting you telling why acrylic is not a reliable option (as you said on the first video) for the frame, because I always though it is better than plywood and mdf. I upgraded my jelly 8mm plywood for acrylic with the same 8mm, and got much better results.

  4. Have other gotten the ordered parts yet? Ordered all of mine same day as 1st video but more than 1/2 hasn't left china yet.

  5. Do you have a link to the drawing of the frame's? ( would be nice! )
    and also a question?
    would you mount the X axis motor, on the other side?
    or should you do once your thoughts over this or perhaps give an opinion on that.
    I think this would be even more easily, the frame can then be wider.
    (1) and it is become easier to make a box of the printer.
    (2) this also in order to make everything more stable!

    greetings from the Netherlands!

  6. interesting that it's already more expensive than the chinese i3 copies that use the same parts. Will be interesting to see the results for comparison.

  7. Hi Tom! Looking forward to the build. I found all the fasteners from one supplier apart from the M3x18 cap-head (DIN 912). The closest they have is M3x16 or M3x20. I'm unsure at this point what they're going to be used for. Will the 16 be sufficient or do I need to find 18s?

  8. I have been going through all of my orders just to verify I havent missed anything and I noticed that there is no glass for the bed. pretty new to 3D printing and wasn't sure it was needed. just thought I would ask and if so what type and size? Thanks

  9. Can you tell me the important parts that i will need to start up and after that i will print the other parts when i will make the printer like cover,psu etc i want your advice just to be sure. thank you

  10. Can you help me with this part from your list "GT2-2M 16T idler pulley, 3mm bore". It's pulley with teeth or not?

  11. I just got a question regarding the printed parts: i see in your website that for y-corners.stl we need to print 2 or 4, but it is not clear for me, in your site it states: 2 for 350mm Y smooth rods, 4 for 330mm Y smooth rods
    that means we need to print 6? or it depends on the length of the Y-axis? (330 or 350)
    the same applies to y-corners (open) x2.STL but I think we just have to print 2 right?

    I am making a BOM list for building mine, and before bolts, nuts, washers, frame and printed parts i am at 150 euro, everything from AE, which is great!
    thanks for your guide!

  12. I've been trying to free sketch this Frame Template as it will not Print Out for me correctly. Problem is when I load the files I can find for it in say sketchup to get the Measurements they seem smaller than what you have here. Like for instance you used a 10mm bit to start the hole in the bed for the bearing slot but all the files I can find on the frame they have have that as 5mm max diameter for the Bearing Slots.

    Really wish Josef Prusa or Someone would would supply a Draft Layout of the Frame and Bed.

  13. Hi, I've just started to build this prusa i3 for a High school project. But I have some problems. I've printed the parts in PLA but I'm not sure if it's the best solution because I started to assembly and my Y corner is cracked. I want to know if I have to Print with ABS.

  14. ich hab ne Frage. (offtopic)

    Ich soll einen 3D Drucker für meinen Betrieb bauen.
    der preis spielt nicht wirklich eine Rolle, aber es soll 1. etwas akzeptables bei rauskommen, 2. muss alles per Bankeinzug bezahlbar sein und 3. muss man jedes Teil einzeln abrechnen können.

    Wenn du mir da weiter helfen könntest währe das toll.
    Mit freundlichen Grüßen,
    Erik Sievers

  15. @frame & bed material: Is it wise to go with 18mm bonded resin-coated plywood ("siebdruckplatte") instead of OSB, which hasn't a nice finish…

    moreover: can I use the 18mm bonded resin-coated plywood as bed material as well, or is that too think and heavy? should I choose 10mm MDF as tom did?


  16. I'm adding the sum of the prices on your blog and compared to the Anet A8 you seems to be VERY close in total price ( like 10$ ) of parts versus the price of the kit of the Anet. That is without the price of the 3D printed parts. Considering the time it would take to order alllllllllll of these and cut the frame, The Anet seems to be a better option. Thoughts ?

  17. Doing some fast numbers in my head, I belive buying an Anet A8 is cheaper 😛 But maybe once I get one, I get into this adventure.

  18. Hello Thomas,
    I'm trying to buy the original printer prusa, but the waiting time for this printer reaches 2 months. Could you tell me another equivalent model so that I can buy it?

  19. are there any dxf uf the milled parts avaible? Cause I have a desktop milling machine, a Stepcraft 600. I would like to mill the frame based on dxf drawings! Didnt find it on github

  20. Hmm I wonder if OSB is stronger than mdf…. They are both pretty tough stuff. I did some research but surprisingly couldn't find any hard data on the subject.

  21. Hi Tom, while searching for Nema 17 stepper motors i saw 2 different type ( one 1.8 degree/step and one 0.9degree/step) Which one should i choose ? granted the 0.9degree/step is more expensive

  22. This is just the thing I was looking for. I'm just getting started on my Wanhao duplicator and I'm quickly realizing that I want more printers for different purposes. This would be an excellent first build to cut my teeth on.

  23. You mentioned Home depot, I went to home depot to pick up some plexi material before and because they only have fairly large sheets and the amount I needed was about 1/2 square meter, they just gave me the trimmings from someones that got cut to size for free. Apparently they do that will all of the wood and drywall scraps too.

  24. Lol. I've actually used trick at 11:02 in industrial packaging machine when stepper counter aluminium clutch broke and I had to get machine running quickly. It was to be temporary solution but machine has been in production with it for I think now 3 years 🙂 I used soft pneumatic tubing for fix.

  25. Please and I am sure you this request, title the videos part 1 2 etc on the top or group them so we can follow it easier. Thanks

    Here are replica NEMA 17 motors for less than $2.00 a pop 😉

  27. I just remember Prusa said : I wonder why there are no MK2 and MK1 cloned out there?

    I just doing some modification 😂😂😂

  28. I haven't seen any comments regarding the prices for bolts and hardware on that webpage . 100 stainless m3x40mm cap head screws for 3.44 euros which converts to ~$4 USD is amazing. I can find anything in north america for even twice that price. Does anyone know where to get prices like that in north america?

  29. Hey Tom! I really enjoyed this series! I would love to see how you'd apply this same ingenuity to making something crazy like a budget printer with a build volume of 1mx1m… Maybe in another series some day?

  30. Man, you rock! Thanks for the video! You help a lot people from countries with weaker economies, like me! Cost here matters more than anything! Thanks again!

  31. Hi Thomas
    Great video, I would like your help if you can share the specification about stepper motors used on your project (X,Y,Z, E)?

  32. Anyone doing a project like this – spray adhesive to glue the paper down is WAY easier than gluestick. I always keep a can around for these sort of projects.

  33. Könntest du deine neue 2018/2019 Version von diesem Projekt machen? Am besten eine Version, die nicht so billig wie möglich ist, sondern eher mit gutem Preis-Leistungsverhältnis…
    Alternativ würde ich mich auch über eine Anleitung/Tipps freuen. Dann kann ich den Drucker selber bauen und dir dann berichten.

  34. Hast du die Stepper nach Augenmaß fixiert? Sollten diese nicht exakt ausgerichtet sein, damit die Welle am Ende nicht eiert? Frage nur aus Neugier …

  35. Very odd background music in this, very very faint but enough for me to check if it was local ambient or in the vid ??

  36. This is fantastic. I think i'll make this thing just for fun as the first serious project when my new CR10S arrives.

  37. Absoluter Quatsch, man kann auch einfach einen Anet A8 kaufen, der ja ein Clone vom Prusa ist.
    Kostet 120€ und somit günstiger wie alles einzeln kaufen und basteln

  38. thank you very much for your video. I liked it and I have a question, where I can download drawings of the main frame? In advance thank you !

  39. Now build the most expensive version. Lol. But seriously. Some parts are cheap and I wonder if quality matters in all areas.

  40. As a relative novice to 3d printing, you've given me lots of information – perhaps too much, but I've enjoyed every minute of it. Thanks!

  41. 9:25 you could print petg or pla ones and they'll be silent ;3 there's one on thingiverse that uses pla strings to ahve less play

  42. If you are buying bearings, I can strongly recommend buying them from industrial resellers. I had a set of din 608 (I think) bearings on my longboard made by KSK, which lasted around 1000km with no maintenance required, it also offer you to get the kind you want (i.e. open, closed, sealed etc). And of course they can be a lot cheaper, I ordered mine together with a friend due to the minimum quantity required, but I remember paying around 12€ for a set of 8.

  43. Thomas, you probably won't notice this comment among the thousands you have but, I have an excellent tip for materials. Richlite, it is very stable, doesn't transfer heat and is less expensive than aluminum. It's made from highly compressed recycled paper and phenolic resin. Compressed at very high pressures and very high heat. It is stable machinable and produces extremely stiff parts from the sheets they provide. Though very few people in the 3d printing industry know of this product it is far, far better at producing stiff frames than even aluminum, because it has similar stiffness with greater weigh per part, does not transfer heat, less cost and is much easier to machine. Peace.

  44. Next time you should try birch plywood. It is the best plywood quality available. The only drawback, it is quite dense and heavy.

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