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Ender 3 Mod - Y Axis Tensioner

by Cornely_Cool Sep 13, 2018
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I want to thank Cornely_Cool for this awesome remix, it is by far my favorite Y tensioner after trying a few.
for me the body of the GT2 did not slot properly into my ender3 for some reason.(my printer is perfectly calibrated)
so I did a slight adjustment and it fits perfectly.
I would like to share it in case anyone else has the my same issue.

Ender 3 Mod - Y Tensioner Body GT2 2040 Vslot version

Please, describe the problem, otherwise, your comment is useless...

Pardon me, I did not want to go into too much detail since you said in the description you were tired of people complaining.
for me the V slot part is a few millimeters off, and as such would not fit into it.
So I compared the designs that worked previously with my ender 3 and cut the V slot portion from their designs, then replaced it on yours and it worked perfectly after that.
I'm starting to think older versions of the Ender 3 have slightly different frames? I don't know
in the picture: the pink is the slot that woks for comparison.

Now is better :-)
What I don’t like are the comments like “it doesn’t work” without explanation...they don’t bring anything to the community!
For this problem, I know that exist several version of V-slots 2020 and 2040 profiles, but I don’t know in detail all the measures (and I don’t know if the profile models between old and new printer models...). All my models are based on the ones I made for my CR-10. I used same shape for X and Y tensioners without fitting problems (on my machine, of course).
Anyway, you can be right, but I will wait more feedbacks about this issue before to modify the model.

If you like I can give you the 2040 version that you can add to your package and is confirmed a perfect fit, I can also do the fix for the OEM version and send it to you, that way your remix covers all ender 3 versions.

The little nubs that slot into the extrusions don't allow the T-Nuts to turn in place when you're tightening it down. I cut them in half with my rotary tool and it worked fine, but something to consider. :)

They don’t need to turn, because you will slide the tensioner from the front face of the extrusion, so they will be already in correct position.

Hi Cornely_Cool - Thanks for the recent refresh/update!

Just BTW, I think Ender OEM uses F688ZZ double sided bearings. At least my Ender did, I know Creality likes to change things around. On the open source github, the BOM says F688ZZ for both X and Y. (https://github.com/Creality3DPrinting/Ender-3/blob/master/Ender-3%20Mechanical/Ender-3%20BOM.XLS)

Because of this one still needs that printed spacer cylinder if one wants to use the OEM bearing to be used with M4 Screw. Luckily, I still have my original M4 to M8 spacer.

So my suggestion is that maybe 1) name it to F624Z version, not OEM, because that bearing is not OEM on the Y Axis? Or, if you wanted to provide an OEM solution, you can a) Keep M4 but provide M4 to M8 spacer as before or b) Provide M8 screw version - but I remember you don't like m8 because it makes part too weak-

Thank you for your consideration, and thank you for your work! I never ever had problems fitting your parts when printed in PLA on two different printers (Ender 3 and Prusa MK3)

I've uploaded also here the files for the screws, in version M4, with adapter, and in version M8.


Hi man, hope you are good!

Ok, i will change the Oem indication.

Due to the fact that now the screws are “universal” between all the “mk7l models, the screw with the adaptor you require, is alrady present in my x axis tensioner page.


First i would like to thank you for your effort, i have been using your pre-update version of X & Y tensioners and i am very happy with them.

Lately i decided to calibrate my printer and noticed that on the Y axis i got some artifacts due to my Y idler wobbling. I started searching for a reliable idler to replace the cheap chinese GT2 and i found a Gates GT2 toothed idler.

After receiving it tho i realized that it's width is 10mm and not 9mm like the chinese ones have. So as you can see i am unable to use them atm since your 5M screw version of the tensioner is designed for 9mm idler width.

Can i request from you to modify and create a version that will fit these Gates idlers?

I am including a link to their exact dimensions as stated on the Gates .pdf


Thank you in advance.

I try simplify the things by reducing the number of different versions, and you ask a customized one...ufffffff

For 10 mm pulley, you need at least 11 mm slot, so needs to modify the screw and the body (the actual have a slot of 10 mm, so you will be in interference also there).
I will check what is possible to do, but I cannot promise you when I will have a couple of hours free...

I bought the Gates GT2 idlers too and noticed they're 1mm too wide. I ended up sanding the inside of the screw down by a little more than 1mm and used spacers to hold the bearing in place. I printed with 100% infill so it seems to be plenty strong. It's not pretty but it seems to be working. A version that supports these bearings would be great since they're very reliable. Great tensioners by the way... printed and fit without a problem.

Thanks so much for this! I printed the screw and the Gates idler fits perfect. I'll print out the modified body and test that too.

Sure, no pressure, whenever you got time for it.

One more for parts not fitting, will detail as much as possible:

Internal screw part printed horizontally
Body and cap printed vertically

Cap fit onto screw with some teflon lube, but screw would not fit into body even with extensive filing of inside cavity and lube.
Eventually body broke while trying to force screw part in.

I used body version 2.

Printed on an Ender 3 with glass bed using 3D Solutech White PLA (Similar to eSun PLA+/Pro) with the following settings:
Layer height: 0.16
Shell Perimeters: 2
Infill: 80%
Infill type: Cubic
Bed adhesion: Brim (5mm)
Support: None
Perimeter print speed: 45mm/s
Temperature: 215c
Software: Slic3r PE

Comments deleted.

Tolerances are off, It was extremally tight sqeeze even after sanding it down,broke when tried to loosen it uop... rubbish..

Tolerances are ok, and are the same for all my tensioners.

If you break the screw is because you print it in vertical, if you print correctly in horizontal is practically impossible to break, due to the layers orientation. The body is over-dimensioned for the stress that have to support, so I dubt that in normal conditions you can break it...

Please find on the internet how to calibrate your machine and start learn...

Anyway, thanks for be so polite...

Hi, I've just installed your CR10 X tensioner on my Ender 3 using the original M8 screw and it fits perfectly. Will it be possible to print the same M8 screw for this one?

Thank you!

EDIT: I printed it for testing and it worked

Cool im curios it too thank you, does bed hit this one when goes full front abother design whic i printed bed hits tensioneer and i need to modfy it

The bed doesn't hit the tensioner in my case.

thank you ill try :)

Here is a tip if you have trouble getting the bolt through the spacer. Heat up an M4 screw with a lighter and melt it through, then it'll fit like a glove.


these fit together real nice, I printed as they came up in cura, as shown in your pics, vertically, however, the slot in the body pinches the bearings/rollers so as they cannot rotate freely, also, it almost has the belt too tight without even putting the knob on though. so that kinda defeats the purpose of having adjustability. Thanks for the effort though, I printed the y axis tensioner looks like it wont have the same issues. thanks.

Thanks for your feedback!

Can you show me a photo of where the slot pinch the bearings? Just for understand...

Is better if the screw is printed horizontally, give more strenght.

Best I can do is hold the y axis body against the x axis body, the y axis body is perfect, i measured the slot in the x axis body to be about 1.25mm narrower than the on on the y axis body, and yes I get the strength thing I didnt realize that was the recommendation until after I printed

Ok, so the problem is on the X axis, not in the Y...so we are speaking of another tensioner

i dont get it how people are happy with this. was there a previous version that was different? the bolt is not fitting into the body (that's for start)
then the bearing do not fit between the bolt 'fingers'. oh come on

Man, the opening between the 2 arms of the screw is 9.8 mm, and I will keep as it is due to the fact that if you need some more clearance, you can sand it a little (I prefer to have a tight fit on the bearings).
For the body fitting, I can say that, is a common problem on printers that have not been tuned correctly. On the model, the clearance is about 0.1 mm all around the screw, so if you can not reach this tolerance, is a waste of time). The main mistake that some users normally do, is to print the screw in vertical instead of horizontal...

Anyway, thanks for your feedback.

i tested/printed many versions of tensioners. so far this is the only one that is having this kind of issues really but ok:)

I loved the design but have been unsuccessful with this thing. There are a few issues for me. Firstly, the inner part will not fit/slide into the outer mount. It is just too big/tight. If I print at about 97% then it will fit in - quite some difference. But there's another problem even at 100% - and that is that the pulley wheels will not fit inbetween the two arms - it's just way too tight, and the arms snap off because I have to put a LOT of force on them to try and slide the wheel in. So basically that arm-mount for the pully needs to be bigger. So, print at 103% it will now allow the pulley in but of course the arm/screw mid part is now way way too big for the outer mount. So, increase the outer mount size and it no longer fits onto the railing. So, it's a bust for this one. Basically what needs to happen is that the inner screw/mount holding the pulley needs to be redesigned so the pully spacing is bigger, but at the same time the diameter of the whole thing is smaller so it fits into the outer mount. And/or the hole of the outer mount through which the mid part goes is made quite a bit bigger with much more tolerance.

I saw in the picture you printed the inner part vertically - try printing horizontally. I printed 6-8 of these horizontally when testing prototypes w/ the designer. When printed horizontally, I've never had internal parts-fit-to-each-other issues, and use 100% scale for everything.

Thanks for your post. I printed it horizontally and it works fine for me... Vertically doesn´t

Thank you for making this mod. Any chance you could create another version for the 4040 Y axis extrusion of the Ender 3 Pro? I'd be happy to try it out, and would appreciate it a lot. Cheers


Here it is mate! I will wait for feedbacks...

Ender 3 Pro Mod - Y Axis Tensioner

I love this design, but haven't had any luck fitting the screw into the body, I've tried 2 PLAs and Hatchbox black PETG, always too tight.

Can you post again the GT2 pulley version with M5? I'd like to have the GT2 version on both axes. Thanks.

Great design but I'm having issues with the tolerances between the screw and the body. I've seen your videos on the CR-10/Ender 3 X-Axis tensioner how they're coming off the built plate perfect for you, but no matter what I do I can't get them to fit together (reduced layer height, speed, temperature, scaling, etc). The screw and the cap work well after a few twists.

Part of the reason I'm printing these is my belts are slightly too long and can't be tightened enough to proper tension. Though I'm only out +0.1-0.2mm, it's made it too large. Is it possible for a "low tolerance" version of this and the X-Axis tensioner too?

which material are you using? Several users reported that the same problem is more "evident" with the PETG. With PLA or PLA+ I never had a problem. Be sure you print the screw in horizontal instead of vertical.

Between body and screw there is 0.1 mm of clearance all around, so, if you have a 0.2mm tolerance on your machine for such a small piece, you are already out...

I'm new in this world with my Ender 3 and i'm just asking to understand since after so much calibration I think I was able to tune my machine to <0.1mm accuracy ( I will print this models this week to test it! ) and because i'm starting to create Things myself, should I use 0.1mm tolerance in my models? Isn't that to tight? 0.1mm is the thickness of a paper sheet... do "simple" parts like this axis tensioner really need so low of a tolerance?

Thanks! :D

really you can use which tolerance you want in your projects...

Remember that 0.1 mm on a radius, means 0.2 mm on a diameter...so there is plenty of tolerance in my models, even if several users complain about it (I try print my models before post every single version, I am not a 3D printing "master", so if I can print, I don't see why other users cannot achieve it...)
About the tolerances. in my opinion, it depends on the result you want to achieve: for the tensioners, due to the fact they are "guides", I like a thigh fit.
For general purpose details, I normally use 0.2/0.3 mm of clearance in my projects (of course is to evaluate case by case...).

thank you for the info :D
I already printed the screw and nut but i'm unable to screw it in :S
I really like your design but apparently i'm unable to get enough accuracy for this models. In my XYZ cube I get <= 0.1 accuracy but apparently is not enough sadly :(
I think I will try to do a remix of your models with more tolerance :)

slow down the speed...

no speed at all =) I already calibrate all I can in the printer... If I cant print with that tolerance I need to increase it

For me still a mistery the reason why someone print it without problems, and someone else cannot print it...

Diameter of the screw is 24mm, so you should reach the same tolerance of your test cube!
Just for try understand, can you check and post the dimension of the pieces?

and for the nut (inner diameter) I have mostly around 20.55 +- 0.05 but with some points with bigger variations like 20.65 and 20.45 ...

i'm at this but I already print 15 cubes to test multiple step values for each axis and I already calibrate the extruder too but I have a Ender 3, it is not really the top quality, I imagine it is not too hard for the print to get some variation along the print...

My screw as 23.98mm when mesuring horizontal, but if I mesure the diagonal I have 23.92 and 23.94
For the height of the screw I have :

So, from drawings, the internal diameter of the knob thread is 21 mm

The screw diameter is 24, and the dimension from the two flat faces is 16 mm

Attached, some photos of my last “test” model...similar situation of yours, but with more precise dimension on the knob.

This pieces fit good just removed from the printing bed, only removed the brim.

Seems you are too strict on the knob diameter.
Have you used supports for the knob?

My scew flat faces has between 15.94 and 16mm

From my mesurements and compared to yours, my screw dimentions are similar but the knob inner diameter really is smaller, since it is most around 20.55mm and yours is 20.95. this may be enough because i'm able to start to screw it but no more than 1 turn...

I printed the screw and the knob at the same time and as instructed, the screw flat (that is the point of having a flat screw after all :] ) and the knob at the default position ( hole in the up side ), then no supports are needed for this prints.

I'm missing around 0.5mm on the knob thead diameter but I printed booth at the same time...

could it be print settings?

really, I don't know what to tell you...

flat for the screw and vertical for the knob are the way I printed mine.

At least we figured out the problem :-P (normally other user are limited by saying "is not working"...)

i do understand you and I know it is frustrating :P

I just did a cube test (photo attached and measurements), what do you think ? it does not appear to be calibration problem right ?

It must be the slicer settings or the filament quality... I dont see other possibility... Do you use cura? Could I try your settings?

I use S3d, not cura.

The cubes are more than ok in my opinion.

Will be interesting to try some hollow figure (maybe there is a defect that you cannot see in a full filled cube)
Y you can try to draw a small hollow cylinder with defined internal and external diameter (i.e. 25 internal and 28 external) and double check the dimensions after the print.

Now we go deep on the hypothesis field...

hello again!

so... I did 2 tests :

cylinder test as you said ( 28 x 28mm with 3mm wall ) and..

  • height between 27.94 and 28.4
  • width between 27.78 and 27.99 ( i did not mark the X and Y and because of that I dont know the orientation of the widths... xD )
    because of that I create a new test and I will print it soon https://www.thingiverse.com/thing:3732028

most interesting I printed this test too https://www.thingiverse.com/make:677275 and my measurements :

  • x 99.24
  • y 99.76
  • z 99.81

in conclusion, despite having good accuracy in the small 20mm cube with bigger distance travels I lose accuracy.. in the second test I can see vertical lines in the X and Y axis... almost like it was pulley/belt ghosting marks... is it possible? I have booth belts with good tension.


Axis & Flow Calibration test Cylinder 28mm .8mm
by Seltix
Calibration Axes
by Seltix

The height depend also about the layer thickness and settings that you use, for example, if you use 0.2 layer, but the first layer is set at 150%, the result will be not 28 mm (in your case), but 28.1 or 27.9 mm.

Remember that, for the X axis, this kind of printers have a “design” issue.

The estep/mm are not constant in all the stroke of the x axis, due to the fact that the belts are “inclined”, and not parallel to the trolley moving axis.
The result, is a difference of steps between the centre and the sides of the x axis.
When you calibrate the estep, with a cube of 20 mm, will be good for that specific position and generally small objects.
When you will try to print bigger onjects with the same parameter, you will note the difference.

I designed also a belt “straightener” for Cr-10 (but due to the fact that the components are generally the same everywhere, I suppose it can be used also on the ender 3), you can take a look at it find it in my projects (is in 2 pieces, motor side and tensioner side).


hello again,

So, i'm did much research and some testing... not much (photo attached)... and from what I could find out the bigger problem here is the fact that the plastic shrink, even PLA... from multiples sites I could find out PLA can shrink about 2% specially in holes because there is no structure to hold it in place. Off course the PLA Brand will reduce or decrease this effect depending on the quality/features of the PLA.

From the multiples sites I read, I think this one is a must read guide :

After all the tuning, even with a big fan trying to cool faster the print, no success... I even test with "only skin" because I did find out the infill can push the walls out, but, again, no success...

In the case of your models with the 0.2mm tolerance on the 21mm knob means that in the worst case of the 2% shrinking I will lose 0.42mm, plus some accuracy deviation (depending on the printer dimensional accuracy) will result in a non fitting part...

In conclusion, I hope you read this as a constructive opinion, but I do think 0.2mm it's a small tolerance for the majority of the printers :S Off course it will fit for some, depending on the printer and mostly on the PLA, temperatures, etc, etc..., but it will not fit for a lot of people unless they print in a smaller scale line 98~99%..

In the end, I did find a more reliable and less trial and error method, using the Cura option "Horizontal Expansion" with the value "-0.01mm" and it was enough to get a perfect fitting part.

I hope this can help others, I think using this option, at least for fitting parts (specialty the ones with holes), is more reliable to compensate this problem than scaling down/up the parts. If it does do give me some feedback :D

Is always nice to read constructive opinions!
I read what you quoted, and is quite interesting, but anyway at the end, seems that a good calibration made it...
I don't require 0.05mm for my models, and in my opinion, 0.2 mm is more than acceptable for the tensioners use (at least my models).

As I already wrote on old comments, I will not change one my project (in this case is more correct say "my opinion" than the "project"), because somebody is not able to print it. Maybe this will feel like a "hard" position, but I think that one tensioner with too much clearance/tolerance will give more troubles than benefits (pulley inclined, not orthogonal tensioning and similar stuff).
Don't take me wrong, I accept your position! and I like your way to discuss about it!

I am curious of this "horizontal Expansion" parameter, what is doing exactly? (I use S3d)

For me I could not calibrate my Ender 3 to print it by default and fit the parts correctly, it may be my filament (BQ), I dont know (I dont have other filaments to test at the moment) and as you did see all my measurements were correct except the inner diameter.

They are your models after all, i'm not trying to make you change them, i'm only sharing my research and testing. I do understand your position and opinion and it does make sense, I was just trying to understand the "WHY" and the "HOW CAN WE SOLVE IT" about this.

About the "horizontal expansion", that options is exactly for this problem (from https://ultimaker.com/en/resources/21932-mastering-cura) :
"The Horizontal Expansion setting will allow you to adjust the size of your 3D print in the X/Y dimension to compensate for the change in size that happens when the plastic shrinks as it cools. The ability to control the horizontal expansion is important when you're working with precise sizes."

and from my testing setting the value "-0.01" was enough, "-0.05" was already too much.

That wold explain it. And I was able to get good acuracy in my 5 cubes print probably because I set it to print it one at a time.

Then if that is the case it wold explain why many people cant print this models, the tolerance is too low for those cases.

I will try to check my belts alignement and report back if I get any update


Standard PLA which has proved accurate enough on another printer. I've also printed the screw horizontal to ensure strength and because that's what your instructions said.

I've looked at the files SLDPRT you've released for the CR10/Ender X-Axis and I don't think there's 0.1mm clearance the whole way around the screw. It seems like on the flat parts there is, but the threaded parts seem to be the same size. I need to investigate more in Fusion 360 though which can be painful. Update: Okay, there is a 0.1mm gap even on the threaded/curved part. Dimensional inaccuracy is definitely my problem and your file looks good.

Unfortunately having extra long belts courtesy of Creality means I can't really do much to improve my accuracy until I get something like this printed.

Hey try putting a zip tie on your belt to make it shorter temporarily. Or not so temporarily. Fold the end over so the teeth interlock and put a zip tie on it. Now you will have a end and it will be shorter.

Great thing, printed both X- and Y-axis.
Is there any chance that you put a hole in the screw part to fit a hexagon M4 nut?
Would be awesome!

There is no mechanical reason for put a nut.

Oh, so you just put the screw in? I got some M4x20 and put them on without a nut by now.
If I think about it, the tension in the direction of the axis should be enough to have the screw fixed.
I wondered why you didn't at least make the surface flat where the screw comes out but I guess I'll just leave it as it is now.
The screw shouldn't move by the vibration induced by the printer as it is pressed against the screw-part of your design when the belt is tensioned properly.

Would be nice though if we would use a printed part to replace the screw. If we don't need any fixation anyway, we could keep it in the RepRap spirit and just use a printed part where we can :)

In the old versions of my tensioners, I foresee also the nut, but just because another user mention it... that versions were printed in vertical, and the seat for the nut make the section too weak for be used...
The new version is printed horizontally, potentially I can also add the nut seat, but is really useless! The screw is screwed directly into the plastic (the hole is slightly smaller than the screw), and will not become lose with the time (same fit on all the versions of the tensioners, and never had a screw losen)...is not affected by torsion movements, because the sprocket wheels are working on bearings.
So, my point of view is... if one piece is useless, there is no point to use it!
Sorry, but I don’t understand your point about the flat surface...
I saw a remix of one of my tensioners, where one user made a plastic pin instead of a screw... i can understand the RepRap spirit, but anyway, in my opinion, one screw is ways better than a piece of plastic!

Been following this for the last few days as it was getting really close to what would work for my Ender 3.

I got my Ender 3 about 3 weeks back and have found that the recent revision is just different enough that none of the existing Y tensioner options would work well with the stock F688Z bearing. Creality squared up the roller bearings on Y-plate which now places the front left roller bearing directly across from the front right.So for this tensioner to work on my version the eyelet would need to be removed to match the right side of your "Body" part.

Making this modification would also make this suitable for the X-Axis as well (at least for my revision of Ender 3).

I can take pictures and measurements if it helps at all.

EDIT: Added photos

Edit2: Looking at this more, this current design is getting real close to being able to use the stock Bolt and Nut along with bearing. The side opening in the Body is wide enough to facilitate the head and nut. The "Screw" part would just need to be modified to fit the 7.5-ish mm wide bolt with 13.7-ish mm head.

Thanks for your comments and for the photos, now is more clear that the fixing system must be different than X axis version; I uploaded the new files, so this version should match the design of the Ender 3.
Is not possible to use the M8 screw, because it will make the screw part become too weak in the holes area, so i prefer to go on with solution of M4 and spacer (M4 because in this way at least the screw model can match between my other different designs).

Anyway, at the end of the "beta" versions, I will release also the Solidworks files, so you will be able to modify them as you like!

Let me know...

Looks Awesome! Thanks! Got the new body printing now and will report back after work.

Not sure if you have an X Tensioner out there, but I'd suggest keeping your last version for that. It's working perfect on my X.

Please, can you take the dimension in the attachment? Seems the new double support of the ender 3 is different than the old one (and is more correct, because make the belt stay parallel to the v-slot profile...

20mm between top bolt and lower bolts on center.

Hi Cornley_Cool were you going to do one more tweak based on the 20mm measurement?

I think it is already 20mm. I have it printed out and working fine. I suppose the "axle" hole could move up a mil (or half mil) to more center the belt on the rail. But the upper teeth have JUST enough clearance to not scrape.

Hi, thanks for your feedback!
The actual position is the same as the orifinal tensioner, this is the reason why i didn't modify again...

anyway I am not a fan of the "inclined belts" as per Creality projects.

Makes sense. agree on the incline - Some of us tilt the original creality tensioner upwards in the slot to get closer to parallel vs inclined belt since it gives you some amount of play by not fully tightening the bottom tnuts. That way it's possible to get very close to parallel or level. However this end of the belt being parallel doesn't matter as much as the end between the motor and the y carriage. Will print and try out - I have been using your slightly older single height version which worked great for me.

No, I think is ok as it is.

Anyway I didnt receive any feedback...so, I still waiting to know if is ok or not.

Works great, and posted the make! https://www.thingiverse.com/make:549949

Ender 3 Mod - Y Axis Tensioner

Anyway, as already wrote by another user, seems the screws need to be lifted a couple of mm to make the belt parallel to the extrusion beam.

Yes,Lifting the screw a couple MM to make belt parallel to beam is cosmetic but not necessary for function, if belts are not rubbing.

Right now, my belts just barely rub but that is because it is mostly in center of the channel. (see pics) If others have printers where belt is more off center offset, they will rub, and this is where being parallel to extrusion would help.

Added a version 2 of the body with a 2mm offset....in case you want try it!

You can find the X tensioner in the Remix Link, is done for the Cr-10, but can be used for the Ender 3 and similars too!

Hi, so the stock bearing I think is M8 Size, but caliper measures 7m (but I'm not sure how caliper measurements translate to M8). The reason I think It's M8 is because its on the BOM: https://github.com/Creality3DPrinting/Ender-3/blob/master/Ender-3%20Mechanical/Ender-3%20BOM.XLS

Note that Ender-3 is open source now. All the drawings, specs, parts, etc are here:

I do have another GT2-20t pulley (same stuff that I used for the X-Axis) that I can use. This may make it simpler. Which do you think is better? the stock M8 or the Gt2-20t with 5mm bore? (same as X axis.

For me, the best solution is the Gt2 pulley, don’t know if there is enough space for a M8...

Okay cool then gt2 16t 5mm bore should work great. Just like it did on the X axis.

Oh and this tensioner uses m5 hardware but has a 3d pritned bushing for the m8 stock idler pulley. Just an idea.


ENDER 3 Belt tensioner

Ok, updated the files, now you have 2 versions, one for the GT2 pulley, and one for the bearings 4x15x5mm (what i used for the Cr-10).
The pieces of the 2 versions are not compatible, due to different size of the "wheels".

In case you want to use the original bearings F688Z - 8x16x5mm, you just need to use the "bearing version, with a spacer (i didn't draw it because i don't want loose time in find good tolerance for the bearing side...), so, basically is a tube with 4 mm internal diameter and 8mm exterla diameter; lenght will be 9.5/10 mm.

To be considered that the belt position is changing between the three versions, due to the difference in diameter of the wheels.


Thank you for volunteering your time and skill to design a part for a printer that you don't even have. Much appreciated. Wanted to check one last thing as typing is easier than printing - the updated parts were designed so that the belt goes over the extrusion lip on the top right? and returns "inside" the extrusion at the bottom? It's basically opposite of how the X-tensioner works with the belt outside extrusion lip on bottom and inside on top. Pictures attached for clarity.

Ok, so now you hve only one version, that use the OEM bearings, a M4 screw and an adapter; The bearing are at the same OEM position, so should be no problem.

If you want use a GT2 pulley, you will need to draw a new body, with an offset to recover the diameter difference.

I have a dubt about the lenght of the fixing braces, in the Cr-10 I had to make them shorter due to interference with the bed wheels in the maximum forward position of the bed, please check this for me!


You are absolutely right! I did not realize that the wheels do interfere and does not allow the bed to fully move to its build area. Note that the right side wheel is further forward than the left. I've attached the Y plate from the open source file. The Bed size is 235x235mm with 220x220 official printable area but many people can do 235x235 as long as they center the nozzle perfectly.

Body modified, reduced braces lenght of about 7 mm ( if you can/want, try to print the pieces, sorry but I don't have time to check all the drawings of another printer...), anyway the body should be strong enough, so no problem.

If this is not enough for allow the full movement, probably will need to go for a body sypported on the low part of the frame ( like I saw in other projects, but really looks "bulky" so I prefer not to do it if not strictly necessary! )

Hi Corely_Cool - I am an idiot. I messed up. I did not account for the bed coming forward and how far the wheels come forward. See pictures, there is no room/clearance on the right side.

So actually your Cr-10 X-tensioner would have been the better place to start, and shorten the left side a lot (or have the v-slot protrude out more to hold the tensioner)

I'm sorry. I understand if you don't want to work on this anymore.

note that in my pics I have my belts quite tight using the stock tensioner.

Ok, design updated...at the end of the story it looks like the X axis, but with shorter braces...
let me know

Works awesome! Take a look. Looks so clean and professional! Note I have a older ender-3 with offset wheels. Newer ones have even wheels and a double sided tensioner. So this may not work with the newer ones.

[EDIT] - I scrolled up and saw someone else commented!

This works perfectly, but maybe you can keep the GT2 20t version up? So people can choose whether they want to use original hardware with the spacer, or GT2t. Because while I do like the original hardware, I think the Gt2 closer fits the belt (like you originally said) and may better constrain the belt motion from wiggling back and forth. I may want to switch back to GT2.

I also saw your comment about M8 version not recommended - I understand that - and observe that when printed on its side rather than vertically the layers are stronger. Especially if you increase the perimeters, so the strain is stretching the filament, not trying to separate the filament layers.

Since we're at a point where its out of beta, I will post your thing on the Ender-3 FB forums!

I am a little lost in the comments, since they are not in cronological order!
The differences between the new and old serie of the printer are clear, the last design of the body will cover both of the models and will look more “fit” for the v-slott 4020.
Try print it out!

I have to modify the position of the bearings, because the belt is not aligned with the v-slot profile!

I see... so, basically the functioning with the original bearings is the same, with smaller bearings or gt2 pulley will result in an offset of the belt.

I will take a look on it.

Anyway, can you take some pictures in the motor side of the Y axis?

Hi, This is a picture of the motor side. Note that mine is not stock, I added a top idler pulley to align the top of the belt. (https://www.thingiverse.com/thing:2919244)

Ender 3 X & Y Axis Idler

So, I tried printing it and fitting it on my Ender-3. I fitted your updated CR-10 X-axis tensioner to the Ender-3 with M5 hardware and a 20t 5mm smooth idler and it fits beautifully and works perfect.

Some notes

  1. The screw/puller is sized for a M4 screw. However, the Ender-3 uses M7 screws for both the Y and X axis.
  2. I thought, oh no problem, I'll just print out the puller/screw from the CR-10 X-axis tensioner which is sized for M5! So I did htat.
  3. I then realized when I couldn't jam the CR-10 M5 screw/puller in to the body (but the M4 one fit in just perfectly and fine) that some top groove dimensions are actually different and the CR-10 M5 screw/puller does not fit into the Ender-3 Body. The CR-10 M5 screw is too small on the groove. See attached pictures.

So I guess my feedback is, may I have a screw/puller for M5 threads too, that fits in this body? Thank you in advance!

And also one random thing I noticed from the Cr-10 X-Axis mod - It works perfectly with the idler screw threaded in the plastic, but may work itself loose over time? Maybe a nut trap at the back? This is the only only thing I can think of improving, it works perfectly fine without it.

As I don’t have this printer I supposed the components were the same of the CR-10, so :

For my CR-10 X axis I changed the original bearings with a GT 2 pulley, that have different overall dimensions.
For this tensioner i considered the original double bearing, that is why you cannot swap body and screw (the central slot of this version is 11 mm (for double bearing) the cr10 version is 10mm (gt2).

The thing of the traped nut, i decided to go without it, because I saw in the previous versions, this solution was reducing the strenght of the screw (printed in vertical). Anyway, i used the version without nut for quite long time without problems (at the end of the story, the pulleys are working on bearings, so they don’t turn on the screw).

So, basically, this printer have the same oem tensioner for both of the axis?