(Yet another?) Prusa i3 MK3S clone build

Hey guys!

After having bought my first Prusa i3 mk3, taking care of two additional i3 mk3 (not going to add the plural “s” to the end to avoid confusion) at work, and later selling my mk3 to my workplace, I was confident enough that I know the inner workings of the mk3 to the point I could build a clone of it.

In fact, the idea started out as a “custom” i3 style build with the following design goals:

  • 24V operation
  • TMC2130 stepper drivers, preferably in SPI mode
  • Prusa mk52 heatbed or clone (as I have some spare PEI coated steel sheets laying around, after upgrading the printers to powder coated sheets, which was a pain in the bum to source, but I digress)
  • genuine E3D hotend, and preferably a Bondtech extruder
  • sturdier frame than the i3 mk3, ideally a cube, but not a requirement

After summing up these requirements, I came across a guy selling a 3030 extrusion kit for a Prusa i3 mk2 and mk3, known as the Zaribo mod. It was about 60€ for the frame cut to length, pre-drilled and tapped where it was needed, and it came with the smooth steel rods. At this point I knew it’s going to be an i3 mk3 clone :slight_smile:

I ended up buying the frame with the rods, a motor kit locally (for Aliexpress price), where the two Z motors had built-in leadscrews, a Lite6 hotend directly from E3D and the rest came from Aliexpress and eBay, namely:

  • MKS Gen L v1.4 board with 4x20 character LCD module
  • four TMC2130 v1.1 driver modules (I wish I bought 5)
  • MK52 clone heatbed
  • belts, pulleys and linear bearings (although I’ll replace them soon with Igus Drylin bushings)
  • Bondtech gear clones
  • power supply
    I sourced the Y carriage and the PINDA 2 probe directly from Prusa, just to support them.

I’m still waiting for the MKS board with the LCD and the belts and pulleys, otherwise everything else is put together. Also the printer has no filament runout sensor at the moment, but everything is prepared, so an i3 mk3s filament sensor is a drop-in thing.
The harder part will be the firmware. I will try to port the Prusa i3 mk3s firmware to the MKS, as it looks like there are mk2 ports. If I fail, then I’ll go with Marlin… any advice regarding porting the i3 mk3s firmware to the MKS will be appreciated.

Here is how it looks like at the moment:

The Z motors don’t sit at the bottom of the frame, so I could squeeze some extra Z height out of the thing, and I’ll need to redo both X-ends so trapezoid nut hole pattern lines up with the brass nuts. Right now I just printed an adapter, which isn’t a very elegant solution IMHO and it limits my Z height a bit :slight_smile:

Right now, here I am with this project. Any ideas will be appreciated, and any questions will be answered :slight_smile:


What I didn’t mention is the SKR v1.3 board I also ordered, with the 3,5" touchscreen. I thought it would be an overkill for a cartesian printer, since there is no need to translate G code movements into motor movements, like on a delta or core XY machine, and the touchscreen can be a source of mistakes (if you tap on the wrong G-code file, for example).
Then I decided for the MKS Gen L v1.4 with the 20x4 LCD, but I’m coming across the problem of not being able to run the original Prusa firmware on it. Although I’m a developer (IMHO not a good one, but I digress… I deal mostly with PHP and SQL related stuff), and although PHP syntax is similar to the Arduino flavour of C, I don’t think I can do it.

I came up with two solutions:

  1. Run Marlin on the MKS or SKR board, and say goodbye to automated X/Y skew calibration, the temperature compensation on the PINDA probe and my beloved live Z adjust. I know that X/Y skew can be calibrated via G code and live Z adjust as a G code equivalent as well, but I really like it the Prusa way.
  2. Sell all the boards and stepper drivers and get an Einsy RAMbo board, which would solve all my prolems, including those I didn’t mention: both my extruder cooling and print cooling fans are 5V only (Prusa parts I had laying around as spares for the 3 mk3 printers). I can cope with that if I stick with the MKS or SKR boards.

What do you think, which option should I choose?

Okay, so in the end I sold the SKR and MKS boards, and bought an Einsy Rambo directly from Prusa Research. This had the advantage of having the firmware pre-programmed to the unit :slight_smile:
The calibration has passed with flying colours, the measured skew of the X and Y axes is 0.00 degress. I’ve built 3 original Prusa i3 MK3 printers in the past, and my best result was 0,09 degrees until now. The 3030 extrusion frame was worth it really well.

Right now I’m printing a 20x20x20mm calibration cube, and I’m curious how well it comes out.

The XYZ-calibration is only needed on a bad frame.
With the MK3 frame as an example it is impossible to get it not straight.
Normally with the mk52 there is no need for the Prusa firmware (maybe the PINDA2 probe)
But everything works with just Marlin/smoothieware because you can probe everywhere.

The Prusa firmware does a measurement of the perpendicularity of the X and Y axes. With the stock mk3 frame, the results will be between 0,09 and 0,16 degrees, depending on how well the printer was assembled, but even a slightly bent tabletop can influence the outcome by a lot (I’ve personally seen a difference of 0,07 degrees just by placing the printer on a flat and sturdy surface). The nice thing is that you don’t need to worry about it, because the firmware corrects the measured skew.

AFAIK Marlin can do this only manually. Also, live Z height adjust for dialling in the 1st layer is available only via G codes in vanilla Marlin. The PINDA 2 probe’s temperature sensor is also only supported in the Prusa firmware AFAIK. The last thing why I wanted the Prusa firmware for an i3 mk3s clone is that I have three more mk3s (soon two with MMU2S) at work, and I wanted a 100% compatible machine with them, because if the 3 printers at work are not enough, I can still just load the same G code on this printer and help the production a bit :slight_smile:

My next project is either a custom built laser engraver, or a 3D printer with at least a 30x30x30cm print volume, where bed is moving along the Z axis, or maybe an MPCNC. There are lots of interesting projects out there, I wish could build them all :smiley:

Coming up next is a rundown of the costs of this MK3S clone.

1 Like

So here is a basic rundown of the costs of the clone:

  • 3030 extrusions + 8mm shafts - 62,70€, sourced from a local Facebook group
  • motors (3 with classic short shafts, 2 with trapezoidal bolts) - 70€ sourced from a local Facebook group
  • original E3D Lite6 hotend - 28,39€ from E3D directly
  • clone Bondtech extruder gears, complete with bearings and the little shaft for the idler - 14,65€ from eBay
  • Einsy Rambo motherboard - 100€ from Prusa
  • 2004 LCD board - 5€ from eBay
  • GT2 belts (seem to be original Gates, it’s the textile reinforced one) and pulleys - 14,35€ from eBay
  • Mk52 heatbed clone - 41,42€ from Aliexpress
  • PINDA v2 probe, Y carriage + U bolts - 54,95€ from Prusa (the U bolts turned out to be redundant, so I could have saved there 6,41€)
  • 24V 240W power supply - 31€ from eBay (could have saved there a bit, but I bought the PSU from Germany instead of China)
  • Fans were free :slight_smile:
  • LM8UU bearings (10 pack) - 12,25€ from a Slovak webshop (not the best quality - the best ones went to the Y axis, the rest to the Z)
  • Igus Drylin bushings (4 pack) - 18,30€ from a Slovak webshop (for the X axis)
  • 1kg of Dutch Filaments PETG for 10€
  • Filament IR sensor - 0€ (we upgraded the MK3 printers to MK3S before the MMU2S units were delivered and they contained the MK3S upgrades as well)
    This is 463,01€ so far.

The M3 nuts and bolts mainly from the spare set of the 3 i3 MK3s I own, the rest from the local hardware store, except for the T-nuts, I had to buy them online, but I can’t find the order confirmation to check the price. Let’s say it was about 30€ for everything.
The total is 493,01€. (that’s actually very close to the price I paid for my first i3 mk3 including the train ticket to Prague, but that was an exceptional bargain)

Do I have a fully functional and worthy equivalent of a Prusa i3 MK3S? The answer is complicated, I’d say yes and no. No, because of the lack of tech support (but I already know these printers quite well, and the 3D printing online community is very helpful), and because I cheaped out on the hotend. Now I see that a V6 would have been a better choice. I’ll do an upgrade very soon.

Could this be cheaper? Yes, for sure, if I wouldn’t be supporting Prusa Research so much, but the design is theirs, so they deserve a bit of support. I could have saved about 10€ on the Y carriage from China, about 50€ on the controller board and maybe more if I’d be getting everything from China. However I have doubts if the Chinese Y carriage would be precise enough, and with the non-original controller board I wouldn’t be able to run the original firmware, and that’s another tradeoff.

Am I satisfied? Yes, I am. The frame is sturdy, the print quality is just as good as an i3 MK3S, if not better due to the more rigid frame.

What would I do differently? Maybe I would put more thoughts into ordering stuff, in order to keep the price down, and I would definitely go for the E3D V6 hotend instead of the Lite6.

Well, I forgot to show some samples from the printer, so here we go.

The vases were printed with Fillamentum Crystal Clear Smaragd Green PLA, the calibration cube is PLA by Plasty Mladeč and the Calibration Cat is Prusament PLA. The cat was a bit stringy, so I had to tune the retraction. Right now, I’m printing a spoolholder from Verbatim PLA, that seems to be much less stringy. (retraction is set to 2mm at 25mm/s, the initial setting for the MK3/S is 0,8mm at 35mm/s)

Last update to the topic:

  • got a new E3D V6 hotend from Prusa (it was marginally cheaper than from E3D, because of cheaper shipping, and also the delivery was faster)
  • I mounted a Noctua 24V industrial fan to cool the PSU, as it was getting quite hot during longer prints, especially when printing PETG, where more power is required to keep the heatbed and the nozzle on the set temperature. Basically, the nozzle is not an issue as it has a sock installed.
  • since Prusa started to stock textured sheets again, I bought one, so I can have the choice of printing on the smooth PEI sheet or the textured powder coated sheet



And just Beaver’s extruder to print
but nice work, although you start making a copy, but you end up almost 100% rainfall