Anyone build a PRUSA BEAR?

Have a build going of a PRUSA MK3S Prusa Bear. I have swapped out some of the printed parts for milled aluminum and was trying to build a rock-solid printer that is practically bomb-proof.

I think where I went wrong was I decided to use IGUS bearings instead of the standard LM8UU. I have a feeling I am going to take this apart again and rebuild however just thought I would ask it here first.

Has anyone built a BEAR and more specifically has anyone had any issues trying to calibrate it. I have yet to be able to calibrate the printer. Sometimes it fails on X calibration, sometimes on Z calibration.

I pulled the IGUS out of the Z-axis and now it seems to be able to calibrate the Z but the X and Y still fail.

I put the BEAR firmware on it (decreased Z axis because of the 3S extruder).

Are there any tricks to getting these machines to calibrate properly? I basically have 3 variables in this equation. The BEAR kit itself, The IGUS bearings, the Milled aluminum replacement parts.

It seems kind of weird, but I read on the PRUSA FB group once upon a time that you need to use their aluminum anodized rods, or something to that nature.

I am kind of fed up with my LM8UU Mitsumi bearings and rods but tolerating them at the moment. I have had the X-rods and bearings replaced on warranty from PRUSA because the original non-Mitsumi’s wore out and scratched the rods. The new ones lasted 6 months? There is a slight scratch on the top rod again and I will probably just rotate the rod to get the bearings off the scratch mark.

As for X and Z calibrations, the X travel and Z travels have tolerance checks. X can fail if the extruder cannot travel the full length smoothly and without resistance. Also, maybe the belt is loose or the pulley is slipping? The Z needs to travel equally on both ends. If one end is off in length or the bed is not perpendicular to the z-axis, this might cause the test to fail? I’m not too familiar with the Bear mod, but the firmware should behave the same.

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ya, it’s kinda my thought process because of the sensorless homing that the IGUS is causing an issue in the calibration of it.

I’m kinda building a Prusa from scratch so I have cut all of my parts myself and put it together. I got away from it for the last year but I have a couple of large production runs coming up shortly so I am trying to get all the machines running I can.

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I don’t have a bear but on the mk3s+ I have ignus bearings. And a scratched rod just to mention. I had no issues with calibration. However I did put a fan guard and it just contacted enough to cause belt length to fail.

Check for obstructions!

I am replacing the ignus bearings there is ringing I didn’t have before.

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Not being familiar with these printers but aren’t Prusa printers suppose to be rock solid. Is there a problem with them using printed parts?

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The bear replaces the solid on piece frame with extruded profiles. These require ridged connection lost when the back bone of the standard is removed. The regular has a 1/4 inch thick metal frame that everything is hung from.




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I use a lot of ball bushings here in bigger sizes and have used diferent igus versions and especially more old fashioned methods like oilite and garlock bushings. seems to me for that size there should be very little difference. what do you suspect the problem is with igus?

To be honest there is some shuttle butt about motor resonance creating some printing marks. I think that is most likely. The frame is so stiff on the Mk3s. I don’t think it is the bearings there is so little movement. I ordered replacement but I am looking at resigning harmonics as well. hard to say for certain. It comes and goes and seems to be speed dependant. Not sure I am still investigating. It only shows up when I try to print slow high quality prints which I rarely do.

what bear upgrade did you do and how far did you take it? custom firmware or even upgrade the board? i did the bear, didnt have the heart to tear down my mk2 so i picked up a used anet for parts and started building a hybrid of a mk2s/mk3 bear. no firmware for it so compiled my own marlin to meet the spec of my machine. Chris warkocki has a few good videos covering the build. and greg saunier(?) has lots of info on firmware issues.

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btw i use igus bearing on the X and Y axis of my mk2 to help reduce noise. a bit of tweeking to get the right tension on them. and had to slow some movements but the havent cause any calibration issues.

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A few more mods and you will have a nice Ender 3 there. :grinning_face_with_smiling_eyes:

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HI Guys, Sorry been working in shipping for a few days

I have stripped out the IGUS from the X axis and the Z axis, Z axis will now calibrate as it should, X is still failing.

I did not use an original PRUSA to tear down and build the Bear I did it from scratch with parts from various machines. All the printed parts are PRUSA and BEAR, control board is a clone with PRUSA firmware.

think I may have found the issue though. When I move the X-axis 20mm and I measure the movement I am getting 25.2mm. My first thought was esteps. When I went to check apparently the M92 command does not work on PRUSA firmware. their default steps per mm are 100 and the default on most others with a similar setup is 80. I am actually suspecting that the motors are different on a Prusa than from other “standard” motors.

I am on a bit of a hold until the 4th of Jan until I receive my new stepper motors. Just to not have to play the elimination game I ordered a full set of steppers from PRUSA and will just strip and rebuild the BEAR hopefully one last time.

@Loosenut I should have gone back to my clone ender 3 with exoslide and decided to finish that one first. Would have been quicker. I have a huge order coming up end of January and trying to get all available machines ramped up to print it out before the end of Feb. It’s going to be about 10k hours of print time so I’m gonna want everything running.

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AHH the joy of running a business.

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ya, it gets hectic, luckily my wife can change out shorter prints at home during the day. while Im at my day job, :slight_smile: :rofl:

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shocking update, I received my PRUSA motor kit last Friday, 6 days ahead of schedule and only 3 days after order.

Haven’t installed them yet as I went ahead and was working on another project of auto YAW leveling with a factory Ender 5 Plus board. (BTW got it working not an issue) just doing the screen graphics for the LCD tonight and tomorrow. If anyone has an ender 5 plus and wants to try out some new firmware let me know.


That is a miracle! These days delayed shipping is the norm. Nice!

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