Building a Prusa i3

I am very happy with the Prusa I built, and so I am with the Printrbot, which much smaller but it does a nice job too. In fact, most of the parts (on different shades of blue) of my new Prusa i3 have been printed with the Printrbot, but the black ones, which are ABS parts, have been printed with my Prusa.

Having two working 3D printers seems to leave you in a difficult position to explain your wife why in hell you're building yet another one, but somehow I managed. I was curious to learn how this new version from Josef Prusa would do compared to what I was familiar with.

I've done a short picture album of the process with some comments in them whenever something different or creative was done there.

My first impressions are that this printer can work really fast and it seems very stable at high speeds. It feels much sturdier than the previous Prusa's and more stable than Printrbot. To its advantage has the reduced mass of the new compact extruder which I have not mastered in its tuning. At the moment high extrusion speeds are not yet working for me, but I guess it is a matter of grip, current and maybe springs (which I do not have yet in the extruder idler).

On the cons side (or not, depending how you look at it) is that when moving it to another location the whole thing does not feel as solid as the older models. But the advantage is that you can easily turn it into two separated pieces you can carry around or fit in your suitcase. A list of changes I have done to the original design:

  1. Instead of Aluminium my frame is made of acrylic GS (Prusa letters are gone from the top to keep the frame stronger). I could not find an Alu frame in Europe. Link to design file.
  2. Y-axis bed is made of acrylic, so I've chosen a more squared shape.
  3. Acrylic frame holes are tapped for M3 bolts, that worked nicely, no nuts required.
  4. The compact extruder motor I bought had a 9mm long shaft, which won't align well with the Mk7 drive gear and the filament guide hole of the compact extruder. So I made some changes to the compact extruder to make all fit nicely. I also adapted the 16mm hole in the base for fitting an extruder I bought from a fellow reprapper. 
  5. Though I bought 48mm long motors in the hope they will keep my frame perfectly vertical, I was wrong. The steppers still need 3mm for the frame to be vertical. I ended up taping a bit of cardboard to the bottom of the motors.
  6. Prusa nozzle is not yet available so I have used another hotend, but maybe I will give that a shot soon.
  7. I am powering the extruder at 350mA and that seems to keep it for overheating quickly. I used initially 1A and that will set it to a too high temperature in a couple of minutes.
  8. I made a mistake when printing the x-carriage so I could not use the teeth as they do not match my belt. So I used a zip tie to held together the two ends of the belt and insert the result into the belt slot which fitted nicely (there is a picture of this).


robert longshaw said…
im looking at getting one of these prusa i3s made to swap my printrbot+ electronics over to. i was just wondering what thickness acrylic you used? ive had quotes for 8mm and and 10mm thickness laser cut, £55 + £8postage was best by £20 from But not one aluminium fabricator in the uk that i found on the net with laser cutting capabilities would quote me. wierd.

also do you still have your stl files for the printed parts?.. im not sure how to edit .scad files and a few of the .scad files wont open right from jo prusas github, so i cant make stl's from them. if you do, is there any chance you could upload them to google docs or email them to me?..

thanks for your post, was good to read

Miguel Sánchez said…
Hi Robert:

I think printerboard can be fixed to the frame in a similar way (zip ties) but if you think it in advance (which I did not) you can move the holes to the right places so ti can be bolted in place.

I have used GS acrylic, which is a better choice not cracking as easily as XT. I have been lucky enough a friend machined it with his CNC and gave it away.

While laser cut of acrylic is ok (I am using 6mm thick one) I reckon 6mm Aluminium is easier to be cut with waterjet (but maybe more expensive).

Sure, I can share the scad files (I've only changed the extruder design) rest are from here

Please note the github repository contains changes on a daily basis. I am going to see if I can create a branch there for the extruder changes ...
Miguel Sánchez said…
Yep, I manage to get a fork with the few changes I did to the frame and to compact extruder.
Bouha said…
Hi Miguel,
I've been following your Prusa i3 build for quite some time, and I'm starting mine between xmas and new year.
I think you could make the frame at home with your CNC right? Can you make one, two or three for me and how much would it cost? (shipping to Berlin).
Thanks and regards
Miguel Sánchez said…
Dear Bouha:

My frame was a gift from a friend who owns a CNC machine. I am going to ask him about the cost of doing several of them. I will get back to you on Monday, I have no clue at the moment.

Kind regards,

Bouha said…
Thanks Miguel :)
robert longshaw said…
Hi again Miguel

ive got the frame file a edited up now to send off to the cutting service, i took your advice and added a way to mount my printrboard to the back of the main plate by using and a laser cut adapter plate and spacers. ive downloaded all the scad files from the github jo-final branch and turned them all into stl's apart from x-end.scad i get a message when trying to render that says "WARNING: no top level geometry to render". did you have this problem with that file?..
im going to try and print all the required files apart from x-ends this week. Hopefully will have my very own i3 soon.

do have a working version of the x-ends.scad or maybe the current STL file at hand?

Miguel Sánchez said…
Not sure what can go wrong. Maybe I fixed something like a commented part in the scad. I do not remember now.

You can download the STLs for X-axis from this link:
Miguel Sánchez said…
Yes, the part module call was commented so nothing was shown.

You can have the modified source from my fork:
robert longshaw said…
absolute legend,

thank you very much for your help. will have all those parts printed now before the end of the week, i hope.
i will send off my revised frame to get requoted for laser cutting tonight, just as an after thought im going to also extend the z height by another 50mm. just because i can it should still work with 8mm acrylic.

thanks for your help.

will keep you posted on how it goes if you like.
Miguel Sánchez said…
Sure Robert, 8mm should work even better (more threads in the tapped holes).

50mm taller does not seem to be a source of trouble.

Miguel Sánchez said…
Hi Bouha,

My friend has a lot of work in his shop and told me he could not do it now.

I've had a look at Shapeoko/formulor in Germany they have both clear acrylic GS in 6 and 8mm thickness. The 8mm one was 58€ plus shipping cut. You can get the dxf file from my github Prusa3 fork.

Kind Regards,

Bouha said…
Wow! Thanks Miguel, you 're nice to have investogated it :)

I'm on another lead now: a friend has access to a water jet cutter ;)

Will keep you updated :)
Miguel Sánchez said…
I've been warned the previous frame file had the bed holes shifted. Sorry.

Please use this new file instead if you plan to cut your acrylic frame:
Anonymous said…
Check it out:

I like it more then original Prusa
Miguel Sánchez said…
Yeah, I saw that and I mentioned to a group of local RepRappers.

I guess this wooden frame is going to be: cheaper, stronger, requiring less plastic parts and a bit more similar to Mendel90.

The only drawback I can think of is that the printer will be not as easy to put away in a drawer or suitcase.

Some people point out that restraining the threaded rods at the top with bearings will cause wobble, I do not know for sure, as these rods are more flexible than 8mm ones.

I saw it first on eBay:

Shipping gets expensive if you are in Europe though.
Miguel Sánchez said…
I've deleted most of my Prusa3 repo in github. What is left is what I really changed or fixed:

Please note that some links above will give you a 404 Error now.
Anonymous said…
Im a student and would like to start making the prusa i3.
I'm a complete noob when it comes to building things, but im willing to learn.
Do you know any website that can help me build one? I need step by step instructions. I also need a list of parts, and how to setup the software and so forth :s
Miguel Sánchez said…
have a look at:
Miguel Sánchez said…
Some details and BOM at

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