Prusa i3 Bear Upgrade v2.0

by pekcitron Feb 27, 2018
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I just ordered the full upgrade kit for the MK3, and have a question if you have the time. I upgraded to the new Y axis tensioner from the mk3s. Is that compatible or will I need to revert back to the Mk3 parts for the build? Thanks

I am trying to find out what each 2040 rail cut length is if you are to make them. I have several 2040 in 500mm length laying around after some cnc build and want to use them for a bear build. Do you have some excel sheet to find out the length where I also could adjust for different Z height? I got the longest Z screw motor from Zaribo.

This upgrade looks awesome! Since I already own a MK3 and plan getting another, could I get this upgrade and only order the missing parts from Prusa? I wonder if there's a list of parts needed from the Prusa storefront.

Never mind, getting the entire Prusa kit is cheaper than the needed components, even without the frame parts.

Sorry for my late answer but happy you find it out :-)

is there a version of the extruder carriage that is compatible with the new Bondtech 3:1 extruder?

I know the documentation says PLA or PETG, but has anyone tried ABS?

I have printed all pieces in ABS including the MMU2 unit. With only the exception the MMU2 body that it's a lonnnng print and it can warp easy, so this the only part I have printed in PLA.

Thank you serandre! I just received my extrusions and fasteners. I was going to try ABS this weekend. It's nice to know someone out there had success. ;)

Is it possible to mount the mk3 bear kit with the mk2s printer? I ask because in time I will upgrade to mk3 and I do not want to pay twice.

I know there are size differences, but maybe they can be solved by placing the screws and nuts in other positions for the Z axis. With Y axis.... I'm not sure how to resolve the differences.

I don't know if the heatbed guide rods have the same size for mk3 and mk2s, but with modified 3d printed parts...

It is possible but you will lose around 5mm on Y axis. I will create a MK2s version soon :-)

The supplier for the Bear upgrade parts seems always 'out of stock'. Is there some where in the USA where I can get parts?

We are working on this, hope to solve that soon :-)

Just finished the upgrade. =)

Bear Upgrade v2.0 + Bear Extruder 0.6.0-alpha

It prints GREAT! No more ghosting... no more 602 issues... Many thanx for the cool project pekcitron!

But just one question left. I changed the Noctua Fan to a Sunon fan. Do i need to change something in Slic3r PE or just keep the default Prusa Settings?

Oups looks like I missed some comments... Keep all settings stock, the Sunon does not change them.

Comments deleted.

Hi pekcitron,

just one question.

You wrote:

Infill type : Gyroid recommended
Support : No
Brim : No
Detect thin walls : No

But what about "Ensure vertical shell tickness" that is ON in Slic3r Prusa Edition? Should i switch it OFF?

Leave it ON like the standard profile :-)

Hi everyone, I have nearly finished the upgrade and was wondering if anybody else has space problems between the extruder cable holder and the electronics housing.

I have upgraded from the spiral wrap to the textile sleeve to bundle the extruder cables. I find the diameter of the cable bundle is bigger with the textile sleeve. This leeds in my case to the Problem where there is not enough clearence and the extruder cable holder is touching the electronics housing (see my photo). I had to tilt the cable holder slightly to make room. Now it barely fits.

@pekcitron maybe its possible to change the mounts of the electronics housing to make a litte bit more room.
For me it's not such a big deal cause I will next upgrade to cable chains and will remove the electronics and powersuply from the frame (cause of heated print chamber).

@pekcitron Another thing which confused me for a moment was in your assembly instruction in step 12 and step 15 where you have written "8x M3 washers (from original printer)" and "1x M3 washer (from the original PSU lower mount)".
In my kit from Prusa there weren't any washers for the z motors or the powersuply and Prusas assembly instructions didn't mention them either. Luckily I had some with 9 mm outer diameter laying around from another project. :)

Hi K_Lab, thank you very much for reporting these issues. The cover is placed at the same position than Mk2.5/Mk3. If you are on Mk2.5 be sure to print the new Rambo cover that gives more place for this purpose. I think that Prusa also upgrade the eunsy cover on Mk3 recently.

Ok I will fix this in the manual, thank you.

Just looking at this and considering it as an option for the Mk3 I'm planning to get this spring.
One think at the back of my mind is, how about replacing the rods with linear rails? possible?

Thanks for the interest in my project. I highly recommend to use my Bear extruder as well (also compatible with stock Mk3).

Yes you can add linear rails, some members of the community have done that. Be careful it will be quite hard to get those aligned, the tolerances on linear rails are much lower than smooth rods.

I'll probably wait for something more "official" regarding linear rails before I mess around with it. I was thinking of getting the Bondtech extruder that works with your kit, but think I will just use your solution instead.
On a side note, I'm surprised that there aren't more build videos on YouTube, there's lots of live streams of printer builds, but don't think I've found any for the Bear kit.

Hi would it be possible to make the frame slightly bigger and put a bigger heat bed in for larger projects?


Yes this is on my plan but will take a bit of time before going out. You can use my source file (Fusion 360) if you want to try on your own, feel free to remix and share!

Hi could you please upload the whole assembly as step?
Thanks in advance!

Hello :-)
I plan to do a full upgade of my MK2.5. Is there any change in the overal dimensions (L/W/H)? It should fit into my existing enclosure.

Thank you very much for your feedback.

I've already have done the bear printer, now I have printed the MMU2 models and bought the MMU2 parts in aliexpress, but I'm unsure about the 5 gears used in the MMU2. Does anyone knows if it's a MK7 or MK8 drive gear ?

I think those are MK2s hobbed gears, they are smaller than all standard gears. You should find them in the Prusa store

Can I get away with using 2020 extrusions? I have them from a 3D printed I’m disassembling. Thanks

I don't recommend it but you can do it. You will need to modify some of my parts. The Fusion 360 source files are available in the download files.

i noticed it doesn't list how many of each part am i under the assumption i only need to print one of each file?

Those are indicated on the Github, in the manual under "print settings" and "bill of material"

Here for MK3 for example :

I don't recall having any doubt about how many copies of parts to print where required. I suppose you can double check to see if it shows that you need to print 4 copies of the feet, for example.

Can somebody explain what the problem is with the original frame? I've printed over 400 hours and never had problems so far? (I think)

I assume you are talking about MK3. The frame does not have "critical issues" but the idea of the Bear is to improve reliability, print quality, usability and will make it easier to customized.

Some issues I found on the MK3 that are solved with the Bear:

  • The Z axis is still flexible and supported by a not very strong nor accurate bracket (the PSU)
  • Front and back plate are not rigid enough and can bend when tensioning the Y belt
  • U bolt are not holding the bearings correctly. Plus the bearings can slip when the printer is hitting them to find home
  • Hard to customize (no possibility to increase Z axis)
  • More place for wiring and optional parts
  • You have access to Fusion 360 source files so you can do all the mods you like (there is an active community that produce lots of custom parts)

Also, I listen a lot my customers and I am very active in the community, this is crucial to me. I am working to have a community with an open mindset, every questions or ideas is welcome and useful, regardless of skill level.

Finally, in comparison to the frame, the original Prusa extruder has critical issues that have been addressed with my Bear extruder. You can read more here : https://www.thingiverse.com/thing:3226689

Hope that helped :-)

Bear Extruder and X axis

One day I found this project page, and read the notes. That made me grasp my MK3 frame at the top cross beam and see how much play there was forward to back. Then I ordered the parts for this project. Now when I do the same thing on this frame there is 'significantly less' play. I am under the impression that this can result in less printing artifacts caused by constructive/destructive interference patterns caused by vibration. Also it looks really cool.

ah thanks. especially with high objects, i would assume.

Exactly. Now of course you could just build braces out of the most stable filament material possible but, for me this didn't seem very elegant. Honestly I had so many little reasons that added up for going ahead with this project it is difficult to quantify. Plus it was just fun to do the build. :-)

It is also pretty hard to build correctly squared parts

I am finishing up my full bear upgrade on my Mk2S and I can report that the kit from ALL3Dmakers.com is top notch. The parts are nicely cut and cleaned and everything is black anodized.
My printed parts have worked great and the instructions are easy enough to understand.

1 small hiccup I encountered in the build is during the mounting of the Rambo board housing in step 16. The bottom mount attaches to the outside of the Z-axis frame so you have to slide a t-nut down the outside channel, but you already mounted the z-axis top pieces in step 13. So you have to unscrew that 1 Z top support to drop that extra t-nut in. That's not difficult, and doesn't impact any alignments so its not a big problem.

Hi Grobog, thanks for the feedback. We worked together with LDO and All3DMakers to produce best extrusions possible. Annodization is made after the CNC cut and tapping to have stronger thread, help with manufacturing and beautiful look!

I know about that glitch in the manual, it is in the list I will fix once I have finish my extruder ;-) . Thanks for reporting it!

I found this design really awesome and i'd like to build one for myself. But! There are some things in that i want to be sure before i start.
First of all is the lenght of smooth rods for all axises
I know the smooth rods are taken from Original Prusa printer (which i don't have) so i found some information about the lenghts:
X axis - 370mm
Y axis - 330mm
Z axis - 320mm
The question is: the lenghts are correct?
The second thing is the height of Z stepper motors.
Are they 38mm?
And the last thing i wan't to know is lenght of the threaded rods.
I hope to get the answers. That would help me a lot!!!

I have complete my Bear MK3 Full clone from scratch (bought everything from aliexpress).

Yes the smooth rods are correct (but some aliexpress sellers sells the Y axis with a 350mm length). The Z stepper motors trapezoidal length is 320mm.The z motors are 34mm and the holding torque is 2.2kgf each. As I said I have bought everything on aliexpress.

But I advide that the MK52 heatbed sold on aliexpress I bought have a common magnets, so after the bed temperature goes above 80C the magnets becomes useless, I have to buy high curie magnets to replace.

Also the X/Y/E motors I have is not original from prusa so the Prusa firmware has to be fixed to work with the sensorless homing.After the tweak the printer is working flawless.

Thanks! it will help me.

Everything is similar to original Prusa printers, no need to change motors or rods. Your rod lengths are correct. The Z motor is 34mm thick, threaded rods are 320mm. Z motor datasheet is here : https://github.com/PrusaOwners/prusa_docs/blob/master/mk3_parts/LDO-42STH34-1004L321E100CM-RevA-for-3D.pdf

Snap-on vertical spool holder: https://www.thingiverse.com/thing:2140685 (PETG because PLA is too stiff to enter v-slot)
MK3 feet adapter: https://www.thingiverse.com/thing:2923082 (very quiet, maybe TOO quiet!)

filament spool holder clip-on rail 2020 openbuild v-slot
Original Prusa i3 MK3 foot holder

What are the specs of the original Prusa MK3 Z stepper motors ? I have bought a pair from Aliexpress and I think they are only 2.2kgsf each.

Am I to assume that if those two plates near Z-motors, if they are even slightly forward from perfect center, that they will obstruct the Z-motor holders?

Yes it is handled in the assembly instructions ;-)

But still would like to improve those Z motor mounts to have more clearance

Yep, it wasn't really a big deal to get the plates in the correct position after all.

Anyways, you have done a suberb job on this project, and I was surprised to see my first PETG prints after upgrade being notably higher quality, particularly the smoothness of layer lines, much less visible. This is one hell of a strong frame.

Sadly I cannot recommend makerparts.ca as a supplier. My full MK3 kit did not ship for 10 business days or something, and when it did, it was not what I ordered. I wanted silver, but the rails came in black with scratches on them and bits of shredded metal here and there, but the plates are still silver, and for the price I paid that was disappointing. The cuts, however, appear to be very accurate, comparable to Prusa's precision.

Again, WELL DONE SIR. You are an asset to this community!

P.S. By the way, my reasons for purchasing this upgrade was not just for increased rigidity, but also it is an elegant way to get the PSU away from all that heat by not attaching it to the frame. For this reason alone I would recommend it, the stock design allows the PSU to get far too hot for my comfort level.

Thank you very much for your kind words, really happy you like it!

I am very sorry to read that from makerparts.ca, they are serious. Did you try to contact them by mail to ask for an exchange, they should accept it normally.

Oh I don't like it, I LOVE IT! :-)

I'm not going to worry about makerparts mistakes, the parts are fully functional and I'm sure they would do an exchange, but I don't want to spend any more time waiting for mail. I just want to print!

Does the MK3 Full upgrade really uses a build helper 106mm? I can't align the PSU with the psu_lower_mount holes, the psu is too far away.

Hi Serandre, yes build helper is 106mm. Could you measure the dimensions from the attached file?

Thank you very much for this picture. Looking at it I have done something wrong. I've printed the psu_lower_mount with a very different size (tiny) on the Y axis, hmmm I've printed from the one from the non vslot remix. I'll print again the correct one.

Happy you found the issue :-) . Could you confirm that you mixed the files, just to be sure there is no issue on my side? Enjoy the rest of the build!

Yes. Somehow I did mix the files, so there's no issue with your files, I've printed it now and it's perfect. Thank you

I’m qurious... do I need an original prusa printer or can I source eclectronics and hardware to build one?

Several people have build from scratch printer using this frame yes. Getting the same specs of a MK3 printer is going to be hard and will cost more than if you purchase the printer from Prusa.

I want to upgrade my mk2.5 to use Einsy board and I am using 12 Volt heatbed with your full mk2.5 upgrade frame. Can you do a mirror y_motor_mount.stl?

Why do you need a mirror of the Y motor mount?

Einsy board need reverse connection on MK3 and I use 12 volt heated bed on full bear mk2.5.
your full bear MK3 have reverse y motor mount.

Comments deleted.

Can anybody re-design this light holder for the Bear frame: https://www.thingiverse.com/thing:2120195/files

Prusa i3 Mk2 LED light bar

I have glued led strip on top of the top vslot and it works fine

If someone needs a Spoolholder, here you go:


Bear Full Upgrade Spoolholder with Bearings - V-Slot - Click&Go
by KappaMi

Hi, just mid-build of a full-upgrade right now. I created this right-angle jig clamp (https://www.thingiverse.com/thing:3044201) to assist in making sure the frame is perpendicular. Not sure if something like it already exists, but it made building the frame so much easier.

I also made a spool holder and filament guide for it (https://www.thingiverse.com/thing:3044226 and https://www.thingiverse.com/thing:3044236) as well.


Right Angle Brace for V-Slot Bear Upgrade - Helper tool
by jgrg1
Prusa i3 Mk2S/Mk2.5 Style Spool Holder for Bear Upgrade (V-Slot)
by jgrg1
Prusa i3 MK2/S/3 Filament Guide ClipOn - for VSlot Bear Upgrade
by jgrg1

I just had a problem with endcap for 2040 alu profiles, they don't go inside profiles, probably because of not perfect printed settings

Nice job! I like your filament spool holder and your black rails. My endcaps fit exactly - a perfect friction fit.

My spool holder will be no more used when I will finish my printer enclosure. almost finished but some details. planned to put a fan who will be active only when tempereture to high, LED inside,...

Try to re-print your end caps and let me know, should not be a problem to fit them in. Keep me in touch!

I am also thinking of a drawer for my enclosure, would be so easier to work on it. Just be careful to get good drawer's rails because of vibrations

I have good drawer's rails because my GF is cabinet maker and she has 2 really good rails recovered
I will add today my actual job on my profile, have a look soon on my things

I also would like to make and enclosure. Yours looks very nice. Please publish your plan dimensions and material. It will give me ideas and same me a lot of time!

And I just have a problem on step 12 :


When I try to put square nuts on hole,. I can't push enough to screw the screw from the top. maybe because my printed part is not really good, it's the only one problem I had, maybe you can do the rectangular hole qhere we put nuts a bit deeper ? Finally I reduce the nut and do a bit round on 2 corners

And I just have a problem on step 12 :


When I try to put square nuts on hole,. I can't push enough to screw the screw from the top. maybe because my printed part is not really good, it's the only one problem I had, maybe you can do the rectangular hole qhere we put nuts a bit deeper ? Finally I reduce the nut and do a bit round on 2 corners

Thanks for the feedback, I have checked the tolerance and I agree it is a bit tight, I will improve this. Also, some times there is some small pieces of filament from bridging that get stuck inside and avoid to be able to insert the nut completely. If it happens, try to cleanup the hole with tweezers (you can also warm the tweezers a bit)

Hey you can add this website where I bought materials for switzerland :

They are very friendly, they do a mistake and sent me 6 wrong screws size, I contact they and they send me really quickly new screws as free to replace the wrong one

and the price is almost the same as others website with coustoms taxes and shipping cost. 2 days after my order I received it

They do not sell my kit but they sell Openbuilds hardware. It is already listed in my github here :

Be careful they are making mistakes regularly :-D

oh yes sorry, they do mistake but they repair it fast... thanks for answer

I'm now mounting this upgrade with mk2.5 official upgrade and others bearings and motors holders changes,

Really great job with instructions

Maybe you can add a comment in the frame assembly because i mounted the back in front and front in back and see just after mounting y axis

Thanks for the feedback. I am working on the instructions with the help of someone else to also improve my english :-)

I want to build an enclosure. I hope the next version will allow the power supply and computer housing to be located away from the frame. If it is on the frame and inside the enclosure it will be too hot.

On the Full Upgrade you can already do it, the PSU is not used to stiffen the Z axis so you can remove it and place it out of the enclosure.

This might already be answered, but why V-slots? I don't see any carriages riding on them, so wouldn't standard 2020 be cheaper?

Hi KarlZhao,

I am not searching to make the cheapest frame but a good frame. Here are some reasons why I prefer to use Openbuilds v-slot over t-slot (not ordered) :

  • V shape gives the ability to make accurate vertical alignment tabs like on this part : https://github.com/gregsaun/prusa_i3_bear_upgrade/blob/master/full_upgrade/for_mk2_mk2s/printed_parts/stl/rod_holder.stl . Thanks to this, almost no need to use a square to check alignment of printed parts. With t-slot you will need support and it comes with inaccuracy...
  • Openbuilds hardware is opensource with good community, FairShare program and regular contests with very good price
  • Available in Europe and almost worldwide (Misumi is not available in Europe for private customers)! I know you can get T-slots from other places but they does not have the same profiles...
  • V-slot can be used as linear rails (will come on the Bear for the next version)
  • Openbuilds offers a complete set of hardware build around v-slot made for automated machines
  • Openbuilds 90° aluminum plates gives the perfect way to square the frame, even if cut is bad or dust is going in between. Plus 90° plates are very rigid! Check this drawing to see what is the effect of the thickness of a hair on a side of the extrusion : https://github.com/gregsaun/prusa_i3_bear_upgrade/blob/master/doc/effect_of_angled_cut.jpg
Comments deleted.

I'm about done printing parts, and ready to assemble, and I was wondering : Is there a filament spool holder here on Thingiverse ? Can't seem to find one. Thanks !

Here it is https://www.thingiverse.com/thing:2846383 .

You can also have a look on the optional parts here : https://github.com/gregsaun/prusa_i3_bear_upgrade/blob/master/optional_parts.md

I wish you a happy building :-)

2040/2020 Spool Holder

Thanks Much ! I knew there was one somewhere !

Okay, so I have already built the Bear MK2s full upgrade which works fabulous... My question is.. If I do the MK3 upgrade kit from Prusa, will the MK2s Bear upgrade frame still work?

Thank for build and feedback, very happy it works well for you! I have not tested and I am not sure it is going to work because of the Y axis. This axis is longer and MK3 is measuring this length. Also Z axis length is a bit longer but the difference should not be a problem.

Next version of my frame will reduce this "fragmentation" and we will have only two frames, the half and the full and they will be all compatible. The only thing is that you will need a new Y axis belt. I am currently working on a rework of the extruder/X axis, once this is finished I will work on the v3 ;-)

Wow . Do you already have an idea when we can see V3 ??

 I decided that I wanted the LCD cover to indicate that it's a bear upgrade, so I changed the "original" text to read "bear". Sharing the file here for anyone who want's to use it.

Very nice thank you!
Check out this one as well:

Prusa Bear LCD cover

Awesome, thanks!

Can someone modify the y carriage to fit the reprap endstop. Im making a prusa clone atm with this setup, thank you!

I know it is not the cleanest solution but you could unsolder the switch and add some wire, then you can use my mount

I was thinking that too, but I ended up modeling it late last night when couldnt sleep, thanks

Thanks for the remix, I am happy you could do it. Do not hesitate to share some pics of your bear prusa clone, would be very happy to see one really made from scratch :-)

Just a heads up: While the RatRig aluminum extrusions are cut very nicely, the screws and nuts aren't the greatest. You should have a metric tap set at-hand during assembly to clear and re-form threads. A couple screws in my kit also had only the beginnings of a hex hole up top, so they're unusable.

Thank you zbrozek for your comment and sorry for my very late answer. These feedbacks are precious, thank you. RatRig is not my company but I have forwarded your comment to them (anonymously) .

kk. I figured you might have a relationship with them. It hasn't been a show stopper - just slowed down my assembly a little bit. No big deal.

You may be interested in the 'drop in nuts' that I developed to 20-40 V-slot extrusion. This allows an anchor to be installed anywhere even if there is no access to the end of the rail.


20x40mm Drop in Nut
by Jimbo70

I just remixed few bits you may find useful or amusing.



Bear MK3 Upgrade Endcap Logo Bicolour
Bear Full MK3 Z-Top Modification For Reverse Bowden

Thanks, love the colors of the Bear end cap!

Thank you. You made me to download and learn Fusion 360 which I am very grateful for!

I am happy to read this! Fusion 360 is very powerful, easy to learn and parametric!

Added a new thing to my Bear collection. :-)


I am just waiting for V-slots from Ratrigs to start building. You may see I am bored. :-)

Prusa LCD Cover Bear Edition Bicolour

I love those two colors! Thanks Karlosek!

Yea. Me too.
Just got a mail from dhl telling me they are delivering the packet from Ratrig tomorrow. Yippee.

Hi pekcitron!
Thank you for this great job.
I did the half upgrade with some little changes for my BQ Hephestos. This works great!
I had some trouble to get all the bolts in the right lenght, so I would recommend to design the printable parts (Y motor mount and idler) for use with one kind of screws (M5x10mm).
But all in all I'm thankful for all the time and energy you put in this work!

Thank you and nice to see that it works with BQ Hephestos!

For now I would like to keep a slightly longer screw for some parts. However, I will work on making parts compatible with standard button screws.

You may want to look at the Y rod alignment tool I designed to help me with the Prusa Bear Half upgrade. It helped me, and the final result showed that no firmware calibration was needed.

Prusa Y rail alignment tool
by Jimbo70

Thanks Jimbo, I have to test this a day to see how good/easier it is!

I also recommend a good quality 250mm long caliper for this (Mitutoyo, Tesa or any other good brand). Digital caliper is really not necessary, I like old style as they are cheaper, reliable and smaller (very useful when measuring in limited space).

I have a long caliper and did it both ways. I found the caliper a little harder. I am interested in your findings.

Maybe I'm missing something, but the STLs don't appear to have been updated here - newer versions seem to be on Github.

Should be good now, let me know if something is weird :-)

You are right, the Z top cap is missing, I am going to check all other files tomorrow. Thank you

I made an endcap with hole in case someone would like to lead the DC leads from PSU to electronics through the back part of 20x40 V-slot.
Longer DC leads are needed for that though. Original leads are not long enough.


Prusa Bear Upgrade End Caps with Holes

I just updated my designs for Multimaterial MK2.5 and MK3 Bear Full upgrade:


It should work now.

Prusa Bear Full Upgrade - Parts for Multimaterial

This is awesome Karlosek! Thank you. Does it work for Full Upgrade MK2s as well?

I do not see why not. The Z-frame is all the same. I will add it to description.

Congratulations for the OpenBuilds contest ! Well deserved. This is a great project well thought out and executed. The build is solid and the documentation is excellent. You deserve to win.

Thank you very much for your comment, I appreciate!

... is the text also on thingiverse? .. not bad

Another awesome upgrade in V2.0.

Im still loving my 2x upgrade machines.

I think i saw the little bear idea i mentioned before, the little logo to add next to the prusa name, very cool.

I am currently working on making an enclosure out of 2020 v slot, may bug you for some custom parts. Still in the design stages right now.

Keep up the great work.

Can I post your pic on the Bear Upgrade Facebook group? https://www.facebook.com/groups/PrusaBearUpgrade/

most certainly, free to post my machines :) thanks again for your designs.

OMG you have too of them! And thank you for the v2.0! The little bear is more because we need to have at least one STL to publish thing on Thingiverse. I still want to do your idea about the Prusa logo, but for now I have this : https://openbuilds.com/threads/thank-you-for-the-powerpack-contest.12027/ :-D

Do not hesitate to contact me for custom parts. I really need to make an enclosure as well!

Your Z-top are having bearing for the lead screw?

yes I am running 608 bearings at the top of the Z axis. Soon making an LED holder for them off the power supply for night time printing.

The cage will be made of 2020 profile with plexiglass. I have a few models saved from thinkgiverse and openbuilds will supply the raw materials. Ebay has plexi for about $30 USD per face. Can use wood on the bottom and back to save cost.

Z axis bearing mounts located here:

Bearings: 608zz

Prusa I3 MK2 Z-Axis-Top


I might be a dolt but..... is there an assembly manual someplace? Preferably with lots of pictures : )

** Found It ! The GitHub page opens the assembly manual with the pix embeded. Thanjks again for this awesome upgrade

Yep, I love project with nice documentation :-D

My build is coming along great - just a question though: Is there a v-slot compatible reel holder?

https://www.thingiverse.com/thing:2537713 works. It merely depends on the dimensions of the extrusion, and not the shape of the slot.

Bearing Spool Holder for 2020 2040 3030 Extrusion
by denos

Nice, hope you will like it. Not yet but it is planned to do it soon :)

I have cheap China i3 that stopped working and I threw away the frame parts and kept everything else. I'm going to look into doing this with some spare v-rail aluminum I have lying around. Could I make this and sell it on E-bay? I have a Mk3 coming next month and would like to recoup some of my losses.

Note the height of the clone's Z-axis steppers. If they are larger than those in the Original Prusa, the dimension of the z-rails may have to be changed.

This is true, good point! You might need to raise Z motor mounts a bit, which will increase the Z axis height. In this case you should order longer V-Slot for Z axis (the 356mm ones on MK2)

First of all thanks for asking! If you sell only one and add a link to my github then go for it! I would be happy to help you buying a Mk3 :)

Just voted for your build! Do you have a Patreon page?

Btw, I think I'll cut the z-axis 10cm longer to fit the 420mm lead screw motors from Zaribo.org

Thanks for the suggestion. I just completed the full upgrade after getting longer v-slots (Openbuilds) and rods (Misumi). I recompiled the Prusa 3.1.3 firmware and it works quite well. I am using the Zaribo steppers.

Wahoo thanks for the vote! Really happy you like it :)

Yes I have a Patreon page (and tons of idea to make) : https://www.patreon.com/gregsaun

This is a very good idea for the 420mm lead screw. Would be nice to have some feedback on this. Be careful when doing the XYZ calibration, I do not know how the firmware will deal with a longer Z axis.

It's ok as long as you edit one line in the fw. Btw, Zaribo is also issuing a binary FW with that height.

Nice! Is it the #define Z_MAX_POS 210 line from Configuration_prusa.h to update?

Yep, is that one

Bigger PSU (350 W) cover that I designed for this upgrade:
I bought the PSU long ago by mistake and decided to use it for the build.

PSU 350 W Cover

Nice. The one really weak point in my Prusa history is the PSU. One shorted another died in its sleep. I only use genuine MeanWell PSU now and have had zero issues. Going to modify this build to accept the slightly different dimensions and layout.

@pekcitron I will take the measurements required off the MW and post them to the Github page where you asked for the MK3 PSU specs.

Joe B
P.S. The Prusa replacement (Chineseium) is $58 the MeanWell is $48, go figure....

Perfect, thank you very much!

Nice! All the power to supply a Rasperry PI, leds and ventilation system! I think that is the first mod for the v2.0, thanks for sharing :)

I too have the MMU, as another commented. I'd like to do the full upgrade when I receive my 2.5 upgrade, but I'd need a way to hang the extruders. Is there anything available to do this with ? Thanks ! Can't wait to get this going !

I did something similar for MK2X
Might work for you as well.
I can edit the design for different alu extrusion.

Oh, I also have designed switch board box support that can be mounted on the frame. Just let me know if I should post it.

Prusa i3 MK2-X Multicolour Extruders Holder

That looks like it should work ! Yes, I'd be interested in the switch board box mount too. I'm rapidly talking myself into getting started on this. .The MMU upgrade for the MK2.5 is still a ways off, but I think I'll build this now, and change what ever needs changed when the time comes.
Thanks Much !

OK. I have to adapt it for different alu extrusion size. Will upload it soon.

For screw length, I am using 5mm thick for m5x10 screw (you can go up to 5.5mm if it is really needed). M5x8mm works great with 3.5mm of plastic.

That looks awesome, thank you Karlosek! In case you need 3D models of V-Slot : https://openbuilds.com/projectresources/categories/openbuilds-parts.5/

If this works great I would like to add it to the optional parts. Let me know if you are ok with this.

Here it is:


Feel free to add it to your optional parts. I would be honoured. :-)

Prusa Bear Full Upgrade - Parts for Multimaterial

Awesome thank you! I will add it tomorrow :)

Not now, it is planed for MMU 2.0. I have some things I have to do before this but then why not. Feel free to design it before me if you would like (do not hesitate to ask if you need help)

I think the v2 of MMU is a ways off, and my 2.5 upgrade won't ship until the MMU upgrade is done. So if I read correctly, I can build the MK2s upgrade, and when the time comes, print the parts to change to the 2.5 ? Thanks Much !

Would it be a bad idea to print the corner connectors and 90 degree plates? Would it be strong enough to make it passable or should I just shell out for all of the aluminum connectors?

I apologize if this has already been asked... trying to read all of the comments on my phone. Thanks in advance!

The problem is how much you will be able to tighten the 90° plates, plastic might crack too easily (soon or later). If you really want to do this you should keep at least one aluminum plate on each side of the vertical axis. I know that some have used printed plates on V1 and they seems to be happy with it but I cannot really recommend it.

If you still would like to go this way, then you should add some selective infill around the holes in order to avoid them to crack (plus at least 50% grid infill and 3 perimeters). I use selective infill on all my parts and it works very well. If you know a bit about Fusion 360 then checkout the source file. I have also described this here : https://github.com/gregsaun/maker_cheatsheet/blob/master/3d_printing/techniques.md#selective-infill

Printed parts information

I posted a message about problems I noticed with my build. One of the problems was the printed parts. After further checking the problem is not with the Bear upgrade and is more complicated than I thought.
The latest firmware upgrade 2.1.4 and slic3r 1.39.1 makes changes to the machine which might not be noticeable until you run the wizzard for recalibation. I never ran the wizard until I finished the Bear. But after you finish the upgrade a wizard run with resulting recalibration is needed!

When this calibration is done, even on unchanged machines, there can be a problem. See these articles:

When the wizzard is run it will rewrite the calibation tables in the firmware. The Prusa machines are calibrated by the bed plate and the sensors in the printhead and are written to the firmware tables. It all software stuff! So to fix a problem you need to use a Slic3r modification. See this page:

It is interesting that I never had a size problem before, and now the size problem has to do with holes and not the over all dimensions.

I mention this because when people upgrade to Bear - which i like very much - they will have new printed parts which may not fit and no working printer to reprint.

3-23-2018 UPDATE: got my Prusa 2.5/S upgrade and the parts I had printed worked perfectly (the expert people at Prusa has made the allowance for printing STL files). No problem assembly with the Bear half upgrade.

It does not sounds like a firmware issue. Please check this before anything else :

  • X and Y belt tension, it sounds like your belts have been tight too much. Check MK3 steps 2.35 to 2.37 of MK3 manual (it is better explained on MK3 manual than previous model) : http://manual.prusa3d.com/Guide/2.+Y-axis+assembly/507?lang=en#s8307 . You do not need to apply excessive tension on the belts
  • Y belt carriage runs smoothly along the whole axis (remove the belt to better feel how well it is sliding)
  • Y belt is free and does not enter in contact with something
  • X belt run smoothly as well and belt is not rubbing/touching somewhere
  • Check you are not in "silent" mode (it reduces the current of the motors, so less force)
  • Print something round, like a tube of 40mm in diameter and 10mm in height in vase mode. Measure your tube to check it is not oval.

Do you have a GitHub account? It is much easier to manage and track bugs. You could create a new issue here : https://github.com/gregsaun/prusa_i3_bear_upgrade/issues

more checking and found this is a known problem that is solved by making internal holes etc. larger than needed to compensate.


I hope my Prusa MK2.5 parts I have printed will work. - UPDATE 3-23-2018 GOT MY UPDATE AND THE PARTS WORK!

BTW - checked the things you suggested and no problem. These Prusa printers are a marvel at producing consistent results.

All of my holes are bigger. I am following "standard fit" for drill and threads (check my cheatsheet here : https://github.com/gregsaun/maker_cheatsheet/blob/master/mechanical/README.md ). Sometimes I add 0.1mm or a "long" chamfer depending on the situation.

Are you printing in PETG or ABS?

As this problem exists since a long time in Slic3r I should have seen this during development, as well as other makers building my printer. It is still possible that something is wrong or not perfect on my side but would be great to have more feedback on this. Could you ask on the Prusa forum?

Very nice chart.

I have contacted GitHub and they reported that it is a long known problem and that the best solution is to make the holes larger in the file. There is also a solution to make a change in the Slic3r: Print Settings/Advanced/XY Size Compensation - a negative value will increase the hole size. I tried the Size Compensation thing and it does work, and it does not change the overall dimensions of the object.

I am printing in PETG.

I have also asked Prusa on 2 of their forum question sites and sent an email to Prusa.
So far only one response from a forum member who acknowleges it is a problem but it is just "drilled out" after the print is completed.
I was concerned about the Prusa files becasue I want my parts to fint the new extruder head. Prusa has provided good files in the past so I assume they know what they are doing.

I could have 'drilled out' the 8mm hole in your Z motor and rod supports but I do not have an 8mm drill bit and I though you should know since others will be printing your parts.

This has be interesting for me! I love to learn new things. I am also constantly amazed at how solid my new half Bear looks and feels.

I do not recommend to drill the 8mm holes, I recommend to file them instead. It is easier/safer to get a good fit. I did not try but 8mm drill will be too big for a tight fit of a 8mm shaft.

I am happy you like your new Half Bear upgrade :)

i´m preparing to print all the plastic parts, but here comes a really stupid question.......

how do i download the stl files from GitHub? (I'm new to GitHub)
when i click in the individual parts i get to see/inspect the part in the GitHub page, but don't find a download button
when i check out the page for the Half upgrade, all the download buttons are present, but not on the Full upgrade
I'm doing the Full upgrade btw:)

sorry for the newbie question :)

I know it is a bit weird on GitHub, this is why you can download STL files from Thingiverse too, check the zip files :)

thanks:) preparing for the build, calibrating and will be printing parts today and tomorrow.
metall parts arrive in the mail tuesday (i hope).

will there be any changes to the parts/manual over the next couple of days? (regarding the post here below mine addressing some issues)

It is possible some part/manual will be updated. However, for all changes I update the change log available on Thingiverse and Openbuilds main pages, just check before disassembling.

I like this build, the printer just feels better. But I did have a few problems:

I believe you added the low profile M5 screws to V2 which were not in version 1 - people need to know they need these when they go from v1 to v2.

PREFLIGHT CHECK: you should add to check the z rods to be sure they fit in your new mounts. Mine did not and I needed to use the original mounts. I see no problem with the original Prusa mounts in the V2 frame. I checked your stl files and the dimension are correct. I printed with PETG and my rod holes were 7.87 instead of the needed 8.0.

FRAM DRILLING: I did not have a 5.3 mm drill. I only have fractional drills so I used my closest equivalent which measureed 5.47 mm. It worked fine, and gave me a little micro movement to aid in the alignment as suggested in ASSEMBLY INSTRUCTIONS STEP 4.
The frame drilling aid worked perfectly. I drilled the first set of holes at 5/64 and worked step wise up from there.

THERE ARE ERROR IN FIGURES - 1.2, 2.2, 4.1 - these show the corner braces at the top of the corners, they should be at the bottom. Unfortunatly I did not realize the error untl toward the end and needed to redu these parts.

FIGURE 7.2 - the 90 degree angle is critical but difficult to measure - I suggest getting a small plastic angle set from the hobby store. They are not expensive and are very accuate.

STEP 10: POWER SUPPLY UPPER MOUNTS - the lip which catches the edge of my orginal Prusa frame was not the correct distand from the M4 screw. From my measurements the distance from the edge of the mount piece to the inside of the lip should be increased 1mm.

STEP 12: The nut trap is too small for a hexagonal M3 nut but just right for a square M3 nut. I doubt that many people will have square nuts. Also, I may be wrong but I think the original power supply screws were M3x20. M3x25 are needed. The 2x M5x10 are too short - need M5x12.

The cable ties are fantastic!!!

Last - the Y micro switch mount to the Y motor mount. The holes for the switch are too far forward and will cause an error when the Self Test calibration is performed. I drilled new holes - not an easy job - and mounted the switch so the front (not the switch button) is almost even with the adjoining edge of its mount. Also, the holes are too small for the screws and need to be drilled out anyway.

THANKS FOR ALL YOUR WORK!!!!!! You have done all the heavy lifting.

For those that are reading this, not that this concerns the Half Upgrade v2.0

I believe you added the low profile M5 screws to V2 which were not in version 1 - people need to know they need these when they go from v1 to v2.

I am not sure to understand. On both I recommend low profile screws from Openbuilds. Could give me more details about this?


PREFLIGHT CHECK: you should add to check the z rods to be sure they fit in your new mounts. Mine did not and I needed to use the original mounts. I see no problem with the original Prusa mounts in the V2 frame. I checked your stl files and the dimension are correct. I printed with PETG and my rod holes were 7.87 instead of the needed 8.0.

There were a point about this, but I improved it (explain to use a file if too small, add same test for z_motor_mount on full upgrade). Do you think it is enough now?


FRAM DRILLING: I did not have a 5.3 mm drill. I only have fractional drills so I used my closest equivalent which measureed 5.47 mm. It worked fine, and gave me a little micro movement to aid in the alignment as suggested in ASSEMBLY INSTRUCTIONS STEP 4.
The frame drilling aid worked perfectly. I drilled the first set of holes at 5/64 and worked step wise up from there.

THERE ARE ERROR IN FIGURES - 1.2, 2.2, 4.1 - these show the corner braces at the top of the corners, they should be at the bottom. Unfortunatly I did not realize the error untl toward the end and needed to redu these parts.

This is made on purpose. It is better to have them on top for better stiffness. However, as the back is narrower they will collide with Y bearings, so they are moved at bottom. If you put both at bottom it should be fine.


FIGURE 7.2 - the 90 degree angle is critical but difficult to measure - I suggest getting a small plastic angle set from the hobby store. They are not expensive and are very accuate.

I have added this tip : "put the frame on the ground, the square in the middle and look from top" . Do you have a link to share for your set?


STEP 10: POWER SUPPLY UPPER MOUNTS - the lip which catches the edge of my orginal Prusa frame was not the correct distand from the M4 screw. From my measurements the distance from the edge of the mount piece to the inside of the lip should be increased 1mm.

Interesting, your Z alu plate is coming from a MK2 or MK2s? Or older one?


STEP 12: The nut trap is too small for a hexagonal M3 nut but just right for a square M3 nut. I doubt that many people will have square nuts. Also, I may be wrong but I think the original power supply screws were M3x20. M3x25 are needed. The 2x M5x10 are too short - need M5x12.

Is it too tight in height or large?

The original PSU comes with different screws length and I did not know what was the other one. I will update the part to match with M3x20mm.

It is weird that your M5x10 was too short, it should be fine.


The cable ties are fantastic!!!

Happy you like it. I will publish soon a 4th one for bigger cables (and parametric).


Last - the Y micro switch mount to the Y motor mount. The holes for the switch are too far forward and will cause an error when the Self Test calibration is performed. I drilled new holes - not an easy job - and mounted the switch so the front (not the switch button) is almost even with the adjoining edge of its mount. Also, the holes are too small for the screws and need to be drilled out anyway.

I have double check and the switch's holes are at the exact same position than original MK2s parts. Could you double check these points :

Are you sure your printer is perfectly calibrated? Some issues you have described sounds like the dimensions are just a tiny bit smaller than expected.


THANKS FOR ALL YOUR WORK!!!!!! You have done all the heavy lifting.

I am happy you like it :)

sorry for any confusion I am causing.

the V2 need 10mm M5 screws, the V1 uses 12 mm M5 screws
My MK2 frame is about 16 months old
the nut trap for the power mount is small in all dimentions and M3X25 screws are needed to mount.
the y micro switch mount problem is a firmware update issue - I just posted a new message about this problem.
I hope you keep going with this project!

M5x10 was also good for V1 but they were at the limit and sometimes you could not catch easily the tee-nuts with the screw. This is why I made all part a bit thinner to better accommodate M5x10 screws (-0.5 or -1 mm depending the parts).

I am going to re-print the low power mount to check that nut trap. You are right for the M5x25, I will update to be able to support M5x20 as well.

I will take time to read your links, thanks for sharing the information :)

I have tons of idea to make this project growing

Big thank you for this feedback, I will take time to answer you tomorrow :)

Can we use just 2040 extrusion instead of the vslot stuff? I am finding the v slot verydifficult to cut properly even with jigs.

You will need to adapt the "rail profile" under my parts. If you get Fusion 360 source files you will find two parameters for each part : rail_profile_width and rail_profile_height. However, you will not be able to change the angle because some part are printed vertically. It is not really a problem if you are careful when assembling the parts.

Interesting, do you find V-Slot more difficult to cut properly than other style of extrusion? Check out the distributor list here, some are selling pre-cut V-Slot : https://github.com/gregsaun/prusa_i3_bear_upgrade/blob/master/doc/openbuilds_stores_list.md

Ah ok. That's too bad. I'm not in tune enough with Fusion to do all of that. In a lot of places it's easier to just get 2040 extrusions. 80/20, Misumi, etc. You'd probably have more widespread usage of this if the parts weren't for such a specific extrusion. For example, I have four of these I need to build, one mk3 two 2.5 and a mk2.

I will write a small article for modifying the parts, it is very easy. I will keep you in touch when it is ready ;)

For me a well designed product is much more important than a widespread product. Some reasons why I choose Openbuilds V-Slot :

  • When printing parts "vertically" you will need to support the rail profile, which results in fairly low accuracy. If you put my part on a V-Slot you will see how well the part are aligning, almost no need to use a square and double check alignment.
  • Openbuilds components are also open source which means you can replace any part by printed one for example (or make them with CNC if you have). And with open source comes the community which is very powerful.
  • With V-Slot comes lots of motion possibilities that are much (much) better than linear rods. I will propose later an "advanced" Bear Upgrade with linear rails (using Openbuilds or not, it is not defined yet, I have to do some simulations and tests first)

Did this article ever get written? I'm in a similar situation. I have some 20x40 profile around here, that has 5mm slots I'd like to use. I found the two parameters you mentioned above already, but I couldn't figure out how to change the angle of the profile to something less steep. That way I could make the profile something like 5.05 mm at the top and 5.0 at the bottom draw it to the center of the slot..

Hi ckovacs,

Could not find time yet to write this article, I am sorry. Angle cannot be changed because some parts need to be printed vertically, plus I have made a shape to have angles printed more nice/sharp. This makes difficult to change the angle using a parameter. Most of the time, those tabs are drawn in a sketch called "rail_profile" (check menu on the left and double-click on it), there you can change the angle.

In the other hand, do you think it is really a problem to have angle tabs for t-slot?

Thanks for putting this together, i am just acquiring the bits to build!
A question though - is there any plan to convert any of the axis from rod to v-rail?

Awesome, hope you will like it! Yes I have plan for that, I am currently doing some research on this. It will starts with Y axis and then X. For now I did not stop to v-slot motion, maybe it will be linear rail like Hiwin or Igus Drylin W. However I also choose v-slot to have more flexibility on this

V-slot would certainly be more cost effective :)
The Igus and Hiwin options are quite expensive.

It will be taken into account. There are not too bad cheap linear rails as well

By the way this build is excellently documented and design - kudos!

Happy you like it, documentation is very important to me. As well as community :)

I already upgraded my i3 to MMU, is there a problem if I upgrade to this frame?

If you go for the Half Upgrade then everything is compatible. For the Full Upgrade you will need to print new support for motors and switch board cover. I didn't designed those mounts for full upgrade yet. I would like to wait for MMU 2.0 but if that could be useful for others then I can do it :)

parts ordered! this is going to be a fun and awesome build:)

going for military green colors on all printed parts :)

Awesome, looking forward to see some pics of your frame! You are going for the Full upgrade right?

full upgrade :)

will add pictures as soon as building starts:)

this upgrade looks AMAZING!! NICE work!!

do you know how it is compared to the Prusa i3 Steel frame?

as far as i understood from the comments, this upgrade will give you:
-sturdier frame
-better prints (less vibrations)
-less noise (more silent)
-and a more sexy printer :)

feel free to add to the list of advantages if i have missed some:)

Thank you, I put lots of effort in it!

It is a fair and interesting question, I have never seen p3steel printer in reel so I cannot confirm what I say. Here are some negative points from p3steel I could see (not ordered) :

  • Noise : it feels like the vibration will be amplified by the steel structure and the way it is build
  • Rod holders : look too small to correctly handle the rod
  • Rigidity : I am not a big fan of the mounting they are using. It is clever but not suitable to a speedy and highly vibrating machine like a 3D printer
  • It feels like it is hard to make parts very square
  • They are several errors in the Z axis of MK2(s) and MK3 (solved in the R2 version of MK3 stl files), have they been solved?
  • Customization : my type of build is much more easier to customize. For example you can easily attached accessories like raspberry everywhere on the printer. Plus it is easy to increase Z axis length. And what about linear rails on Y axis, should be easy to mod on mine as well

In your advantages list I would add :

  • Customization (check the point on my p3steel comment above)
  • Maintenance is much more easy
  • During maintenance or when you move the printer, the frame does not change (compared to MK2(s) frame)
  • Full upgrade gives you the possibility to move the printer in an enclosure with the PSU outside for fresh air. This is not possible on MK2s and MK3 because the PSU "rigidify" the Z axis
  • Use same firmware as original printer, as well as much original components as possible : smooth rods, cables, RAMBo cover, PSU cover and even Z axis alu plate for the Half Upgrade
  • Professional manual

Thanks for the reply
going to save up some money and definitely build this!

Very nice, do not hesitate if you have any questions or remarks!