Prusa i3 MK2 X Idler/Belt Tensioner+ v2

by IsmaelPR1 Feb 1, 2017
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will this work on a geetech i3 pro b? what is the spacing on the leadscrew and smooth rods? looks awesome. I'm hoping this will fit

The space from the center of the z rod and the center of the lead screw is about 16.5mm

How does this stop the rods coming out ? It will all be putting tension on the belt to hold them in.

Hi! Could the Igus Rj4JP be used with this design?? I mean these https://www.igus.com/wpck/17748/Motek14_N14_6_3_Vollkunststofflager They are 1 mm smaller in diameter than the RJUM

I have done a rework of this design to use those bearings. Here is my version of the MK2-X design which is a modified prusa i3 mk2 with aluminum extrusion frame. The file you are looking for is: X_END_IDLER_tensioning_idler_V15. I also redid the motor mount for the axis to accept RJ4JP-01-08 Igus bearings (15mmOD) and the tilted noctua fan upgrade by JKSniper found here, highly recommended! The x-axis motor mount is called X_END_MOTOR_tilted_Igus_mounts_V15. Let me know if you have any questions!
Davtr did the first MK2-X here

The Hawk
Tilted Adapter for Noctua UPGRADE Fan + 2x Fan Cover
Prusa i3 MK2-X
by davtr

Finally got these printed on my MK2S after making an enclosure for printing in ABS.

Someone else asked if these eliminated the rubbing/grinding of the x-axis belt on the right-side x-axis bearing, and for me, they did NOT eliminate that issue. Maybe minimized a bit, but not eliminated.

Also, when doing the reassembly, I had a heck of a time getting the linear bearings into the new parts. Once installed, I inserted the rods, and I can tell these parts are crushing the bearings a bit, as they're noisier and not as smooth as before.

Comments welcome, as it very well could be something with the way I printed them.

There is no way that the plastic is crushing or compressing metal linear bearings. I could see that happening with the plastic igus bearings. I personally didn't have that issue.

The metal in these cheap bearings isn't all that great, so while you would like to think they would be hard to deform, I still think they deformed slightly. They were fine before I put them in the new parts. These ABS parts were printed at 90% fill, and are pretty solid. When installing the bearings for the y-axis, with the little u-bolts, they warn you to only get them slightly snug, and don't tighten them much, or you'll start to deform the bearing and affect its smoothness.

Based on all of your comments, I need you to build my next printer, since you haven't had any of the issues that everybody else experiences :)

I personally never had these issues, the slight belt rubbing on the right side is very minor and after almost 2 years with my original MK1 belts there hasn't been any issue with it. As for the 90% infill, that's overkill. I print all my parts at 20% or so. Again never had an issue with proper layer bonding.

Anyone try this on the MK3, or will I be the first? Once you get used to the fine adjustment, its hard to go back to original. Only differences I see in the new parts is that there are no holes for adjustment on the MK3 original part. Rod spacing is almost identical. The hole for the leadscrew nut hole is bigger on the MK3 original as well. That appears to be it. Wish me luck. It would suck ti have to redo it, but nothing ventured...

Will you be able to make a version for the MK3? With the changes to the extruder and how difficult it is now to adjust the belts it would be a life saver

I will post back on how it goes with my MK3. Was there anything you saw which indicated that it wouldn't work? I'm not seeing it, but I am no expert.

Well I got it going on the MK3 build. The only touch thing was aligning everything when dropping the axis on the lead screw. I think some adjustment for the length/tension was in order as I didn't have the smooth rods installed at that time. Everything got better once they were in place. I will note that you will need at least 2 M3X12 screws as the kit comes with m3x10s. These are for the inside lead screw nuts. The outboard ones can use anything that size or larger. Everything calibrated first try and is currently on its third print. If anything you could take the parts and make a cutout for the idler tensioner, and the idler rod holes from the SCAD prusa files. I might do that at some time later myself as a test.

I am still running this setup on my MK3 without issue, so while I am sure there are some differences, I have not noticed any negative results using the originals.

I don't have an MK3, Nor do I plan on getting one. I have two Mk2s printers one converted to a Haribo the other into a Zaribo with multiple upgrades as well. I haven't downloaded the printable MK3 parts so chances are high that I won't be putting together a version for the MK3 but that might change in the future.

Thanks a lot for making this available, I'm sick of having to pull my printer out of the enclosure, turn it around, gut it, adjust it and putting it back. As much as I like my printer, this sort of adjustment could have been included in the first place.

Glad you find it useful, I felt the same way about it myself. Which is why I decided to come up with this.

Hey there, does this modification help the issue with the grinding on the x idler bearing? I've seen other mods that change the dimensions of the hot end carriage, so will this help that problem or should I also use that other modification?

I am not sure that I understand your issue as I've never had any grinding noise on either of my two printers.

There is a common issue with the MK2 and MK2S where the right most idler bearing is misaligned with the x carriage. The issue leads to the timing belt rubbing against the right z carriage, and it causes some ghosting issues for me personally. There are some remixes of the x carriage that make up for the issue by changing the dimensions of the belt loops.

My question was if your design takes this issue into consideration, but from your response I'm sure you haven't experienced the problem!

I have this problem as well, but I read someone else had fixed it simply by reprinting the piece that holds the idler bearing as the original print's dimensions were off. If that's true then this part may address it incidentally. I'm hoping to print this sometime soon, if it helps I'll report back.

Thinking of making this as I have grinding issues with the belt on the pulley, also adjustable would be fantastic!

Would HIPS be ok or PETG? I am not sure if I can print PC successfully yet... lol

There might be too much flex with those materials. You don't print with ABS?

How big are the required m3 screws?

About 20mm or do depends on your rod lengths really.

I made two sets last night. They completely solved my problems, and allow adjustment for perfect tension. The funny part is I wound up realizing how useful this modification was while reinstalling. I forgot to put the Pinda probe, extruder, and fan wires above the X rod before installing the carriage. I took a disgusted pause until I realized I could simply pull the bottom rod out and correct the situation. Very cool. I think you might have been being sarcastic with the 90% comment below. In any event I made 2 sets at 30 with solid layers every 10 in ABS and it seems extremely strong. Thanks again for all your good work! Running prints now...Smooth, quiet, and straight.

Links for Home Depot parts (bolt and nut as pictured) if having a hard time finding them:


I'm late to the party, but thank you for fixing the model. I put Pacific Bearings (Alum shell Igus) on my bed, but when I just upgraded the carriage bearings I noticed a lot of friction. After beating my head against the wall for several hours I came here to check whether or not there were any revisions... Sure enough...

Thanks again for the great work!!! Love your designs.

Yes should work as is. I use Misumi

Hi there
Will this fit the MK3 S version with upgraded bears to IGUS RJZM-01-08 alloy case?


There is no such thing as an MK3 S but it will work with the MK2S. I use it with Misumi bearings that have the same dimensions as the original bearings. Works perfect.

Ok, that is what I was going to ask. You mention Igus but I am using the Misumi bearings and rods on a MK2 original. Just print these parts as they are no adjustments?

Also I don't notice any issue with rod spacing in my current config. How much was the distance between the rods changed?

Is the vibration on the x belt gone after installing this? (the vibration that appears with fast direction changes i mean)


Why do i have to print the motor side of the x carriage ? The tensioner is on the right / idler side ?

What changes did you make to the motor side ?

Does the pressure on the z rods cause issues ?

Thanks a lot!

You will never get rid of those fully. But it will help some.

I would suggest you print both. The rod spacing was adjusted as the stock setup put excess pressure on the rods. They were too close together.

Will this work with PLA or does it need something a bit less brittle? I'm thinking about the tensioning plate at the end.
Also do you have measurements for centre of z-rod to centre of smooth rod? I'm working on converting an i3 econo build to something more robust and planning to replace the 5mm threaded rod with 8mm ball screw but want to be sure the inter-rod spacing of your part will match with the spacing of the existing frame.

It's possible though I wouldn't chance it.

Wouldn't chance the use of PLA or replacing 5mm thread with 8mm ball screw?

Any chance you could upload scad files?

I don't have scad files unfortunately..


It makes you a lot of work to customize the X-End Idler for 22mm TR8x8 leadscrew brass - thank you.


Prusa i3 mk2 x-ends for 22mm leadscrew nut
by bbandi
Prusa i3 MK2s X Axis Brass Leadscrew Nuts Idler/Belt Tensioner

What modification(s?) did you make to the motor side of the assembly?

The rods holes are around 5mm less in depth so that the right side works with the screws that will rest on the ends of the rods when screwed in. And overall the rod spacing on both ends was adjusted to allow for a smoother movement the stock ones create pressure on the bearings.

hi does this mod also work for MK2S ?

The MK2s isn't a completely new printer only a few things are different and the rod dimensions are still the same. So yes.

You can ungroup these parts using Slic3r via the right click option and select "SPLIT".
Once they are split you can right click on each part and select "Save as STL" (They will all have the same default name so you need to change that)
Once you do that you can open the individual STLs in any program you wish and print separately.

Thanks for making this. I can't get this file to ungroup in Cura so I can print it in sections without being locked into a 15 hour print. Can you please split the files.

It shouldn't take anywhere near 15 hours to print these files, I'm not sure how you're printing them. Speed, layer, etc.

I will try to provide separated files later if I have time. Perhaps tomorrow.

I have the newer MK2S that uses U-bolts to hold the y-brace bearings. I want to change over all of my bearings to the IGUS Drylin bushings and also use your new tensioner setup. Can you tell me which IGUS bushings to use? Do I need to change the smooth rods as well? Lastly, does your new belt tensioner use the original idler pulley or did you swap it out for one with a bearing? I find I get a lot of slop and noise from the one that came with the printer and the belt noticeably tilts back and forth with each direction change. I originally had the belt a bit too tight and it was squealing. I would like to change the idler to one with a bearing. Can you make a recommendation?

Word of advice. The igus drylin bearings get tighter if they are compressed by brackets or even by the holders on the x carriers. I personally don't use them they cause binding even on my 2 perfectly built and aligned printers. Those bearings are softer so anything the squeezes them will cause them to be tighter on the rods.

What do you recommend?

I get great quality with the stock bearings. Honestly. I recently installed some Misumi bearings but the gains are minimal not worth the cost for them.

I get so much vibration and I have adjusted them so many times. I have the Y rods perfectly parallel and run really smooth by hand, but under load the tend to vibrate as the plate withdraws to the back under load.

Use these. With having an aluminum shell they won't distort as easily as the Igus/Drylin bearings. Now, that doesn't mean you can crank them down. http://www.ebay.com/itm/162065169736

Fantastic design. I've yet to go get the bolt/nut, but everything else has fit spot on.

4mm hex bolts are really hard to find here... I'll have to remix this into 8-32....

Here's the remix parts for 8-32... Using a 1.5" long 8-32 Allen Head Screw, and standard (non-nylock) nut.


Comments deleted.

Printed this last night and installed it today. Fits nicely and is another great mod to add to my Prusa. Thx!

Glad to hear it!

What materials would you recommend this be printed out of or will any (PLA,ABS,PETG) work?

ABS and PETG will be fine. High infill, as high as 90%

Could you update the thing details to indicate the 90% recommended infill? I just finished a few sets and then saw this. I am going to try them but I wish I had seen this first. Thanks for the great modifications.

You have made some nice mods for Prusa. Will try many of them :-) thx!

Ismael, could you modify/include a version that does not allow the X-rods to come out?
I promise to print one and post a make ;)

Hi. Unfortunately due to the design the rods must come out/go through the x carrier as this allows the tightening force to be placed on the x rods with the two M3 screws on the brace and not put force on the z rods which would cause print quality issues as it would cause pulling/slight bending on the z rods and lead screws.

Hey, can you provide the source file or provide a new version for the IGUS RJZM-01-08 bearings with 16mm outer diameter? That would be awesome!

I use my printers with IGUS Bearings as well so this should work as is. Push things into the bearing space. Done.

How smooth is your X? Using IGUS bearings on X, even the metal enclosed RJZM-02-08 I get a little resistance and drag from the weight of the extruder stepper adding an angular load to the rods. If I remove the stepper / weight / load the x carriage glides extremely smooth. Smoothness test done without the belt attached. On Y using RJZM-01-08 using your mounts :) it's butter smooth with zero resistance.

Glad it's all working well for you!

My bad, i wrote down the wrong bearings in my first post. I got the RJZM-01-08, they do have an aluminum casing. You can't force them in.

The way the design a bigger bearing won't work as the walls will be too thin on the bearing holders and at the time I can design anything for them if I get the time I will try to work on it.