Prusa Bear Upgrade  

Trusted Member

A few weeks ago, I received and installed the Prusa Bear Full Upgrade on my MK2.5. This replaces the frame of the Prusa with 20x40mm V-Slot. I purchased this as a kit from RatRig.
The parts supplied were well cut with all necessary tapping and smoothing already done. There were no missing parts and a few hardware spares were included. I’m very pleased with the parts supplied.
The instructions are adequate but not nearly as nice as the original Prusa instructions. I experienced a few very minor problems.
1) The dimensions listed for the Y motor mount position seemed incorrect. The Y end stop was not contacted by the belt mount on the bed and I had to move the motor mount to correct this. This is very simple and I did not go back and record the new measurement. Just watch for this, I may have done something wrong.
2) I received one bad T-nut. It had no threads. Fortunately, this was discovered early and was not one of the nuts inserted for later use. Check them before using.
3) I had printed all the parts in PetG a couple of weeks ago while awaiting the kit arrival. The only issue I had was the holes for the Z axis smooth rods were very tight. This has also been my experience when printing the genuine Prusa parts. The holes required enlarging. I used a US 5/16” drill bit to open the holes a bit. Now they fit very well. Do this before assembly and save some trouble.
The printer is much more solid now, no flexing at all. Not sure if I can see any actual difference in the printing but sometimes it’s nice to just make things better 🙂
As the mounting points have changed, I also had to re-design and print a new filament holder and the lighting mounts I had been using. I’ll make additional posts when these are available for download.
Here are some links about this kit.
Get a kit from RatRig here :

Posted : 16/05/2018 10:06 pm
Estimable Member

What does this kit improve on the MK3? Just a more rigid frame?

Posted : 20/06/2018 5:28 pm
Active Member

I have the full 2.5 kit on order as well. Should be a fun project. Looks like a very solid design.

Posted : 15/07/2018 2:33 am
Reputable Member

What does this kit improve on the MK3? Just a more rigid frame?

Yes, and better alignment.
Stock MK3 to Bear stock not worth the extra in imo.
But if you take bear and go custom to get a higher Z it worth! You can even put 400m-500mm Z if you extend the cables and replace the rods

Posted : 31/07/2018 7:16 pm
Lee Griffith
Active Member

I kind of want to do it just so I can more easily swap out the y-axis rods of linear rails. 

Posted : 12/09/2019 10:54 am

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