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Prusa i3 Bear Bearing Holders

by pekcitron Mar 12, 2018
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Anyone try these with the SKF LBBR8-2LS?

No SKF requires a press fit into a housing (to press the little parts moving around the bearing).

Hi Greg,

I have a MK2.5 but recently it seems like all of the full-upgrade kits are being sent as "MK3" upgrade kits. Should I print the MK2.5 bearing holder, or the MK3 bearing holder?

I have this same question.. I would probably guess 2.5 as I believe that the MK3 bed frame is different between MK3 and MK2.5 which is what these would attach to. Would be nice if someone that has a 2.5 and MK3 could confirm though.

Hi guys and sorry for my late answer. We are now focusing on MK3 frame only to make development easier. However, I could not catchup yet with the kit and it is a bit messy. You need to use this part: https://www.thingiverse.com/thing:3468567 and read carefully the description.

Bear Y belt adapter for MK2s/MK2.5(S) on Bear MK3 frame

Hello pekcitron,

is it normal that the bearing has contact with the Y carriage and not the holder?

When i slowly tighten the holder the bearing get contact with the Y carriage but the holder is not fully (maybe 0,2mm left) in contact with the Y carriage... i hope you understand i dont know how to describe this in english ;)

printer is calibrated and i printed the holder with 0,15mm

This is normal and useful because of tolerances.

Hi Greg..will these work with igus drylin? I thought I saw those on one of your bear printer..thanks!

No I recommend a press fit housing for Igus bushings.

Hello. Is it possible to make an MK3 version for 16mm RJZM-02-08 IGUS bearings? I have tried to modify them in Fusion 360 but it does not work. Maybe i need more experience but think it does not hurt to ask someone more experienced. Thank you.

I am not recommending those bearings so I prefer to not do it sorry.

Ok. It was worth a shot. Thanks anyway and keep up the good work!

I tested them on Igus rods and they have too much play to me. I think it would be better to go to 10mm rods and use RJM-01 because they have a lower tolerance.

Hello. I have printed the half-bearing housings (1 dot) for my MK3, but upon mounting them, the housings rub on the center frame. Anyone else encounter this problem?

Like you I wanted these for my original MK3 as I am just installing them on a full Bear build. So I decided to try and redesign them to fit the original frame. https://www.thingiverse.com/thing:3558209 Keep in mind that these are a work in progress so if you decide to try them please let me know your results. I should have mine installed and some preliminary feedback in the next week or so.

Prusa i3 MK3 Bearing Holders

All those are made for Bear Upgrade frame only, not compatible with original frame unfortunately. More details about the Bear frame here : https://www.thingiverse.com/thing:2808408

Prusa i3 Bear Upgrade v2.0

Very well. Thank you for explaning that as I’m new to this

i printed these and snapped in a bearing to test em out. there seems to be a little bit of play so the bearings can move around ever so slightly within the holders. are they supposed to be fully snug and unable to move even a little?

Hi Slyph, you should not have play on the external diameter of the bearing, bearing should not "float". However, you might have a bit of play on the axial axis due to imprecision of the groove. Be sure to print the part with 0.15mm layer height (or lower)

In case of the half upgrade, the screws go directly into the material without using a nut. Is that correct?

these look like they may be able to hold the RJ4JP-01-08 have they been tested?

I tested them (as well as RJZM-01-08 in a previous design with bigger diameter) and I cannot recommend them because of their tolerance.

They introduce to much slop / play. I tested them on original rods as well as on Igus rods. Igus rods are important for those bearings as they will keep self-lubricating particles from bearings to reduce friction as well as slop. But even after 6 months of daily prints it still has too much play (but better than the first use).

Igus is doing awesome products but those bearings are not applicable on this type of design.

Hi! I've been reading about using Igus bearings/rods for the past couple of days. Someone recommended using RJZM-02-08 because of the issue that you brought up about the other two having some play. I called up Igus and spoke to an awesome salesman there and he confirmed most people are getting the other two, however the RJZM-02-08 has tighter tolerances. I am getting a sample of all three to see what I can do.

My question for you pekcitron, since the RJZM-02-08 does not have any grooves on the OD to lock it in place with something like this, do you think it would work if I modify the Fusion 360 file so that the housing goes past the ends of the bearing and the bearing has to "sit" into it? I'm going to try this out and see how it works. I might even make it just a slightly tighter fit in the printed part (in the perpendicular direction to the direction the rod travels)

That is very interesting what you are saying here. However I jumed on their doc and RJZM-01-08 and RJZM-02-08 have same tolerance of 0.032-0.070. Here is the doc I used :

What am I missing?

If you make the housing passing the bearing you will reduce the Y axis travel distance. I think removing the grooves should be enough to keep the bearing in place. This is somehow similar to what Prusa is doing with U screws.

Hi Grégoire, Just to make sure - I have the Bear half upgrade (Z-frame from MK2s) and I am mounting the MK3 carriage and bed on it. There are some differences among MK2, MK2.5 and MK3 carriages (those "spiders").
Which bearing holder should I print for my needs?

Thanks in advance!


MK3 carriage has centered holes for the bearings, however, the holes are longer. After checking, the Bear Half Upgrade holder will be good but the bearing will be de-centered by 0.5mm (should not be a problem). But, specially for you, I have attached to this comment an STL file of the Bear Half holder with centered holes :)

Wow. That was fast!. Many thanks for your kindness.

I'm doing exactly the same thing. I've also bought the Einsy board and the 24V MK52 bed. Have you any problem with the other (x, y axis) parts?

Yes. I could not get past the selftest. The x - axis travel is longer on mk3. The z-frame is different on mk3. I am using mk3 firmware as i was able to get all the mk3 hardware. I was not able to use the mk2 frame. I decided to discard the half upgrade and i am currently working on full mk3 Bear upgrade. Well, waiting for the extrusions replacement from Ratrig as the first batch was cut way off the square.

The dot on the half-upgrade parts is missing, does it matter how they are mounted?

Thank you, that was a mistake (Fusion 360 export is very annoying). Half upgrade version needs to have the dot facing outside (because of the original Prusa MK2(s) Y carriage that does not have U-bolt holes centered)

I already printed them without the dot, is there a way to measure/identify the right side?

if you look carefully you will see that the U-bolt holes on the Y carriage are not centered, as well as on my bearing holders. Just align them and that is it. If you put them in the wrong you will clearly see that the bearing does not go inside the slot hole.