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Y-belt tensioner and Y-belt holder for Bear upgrade MK3/MK3S

by RH_Dreambox Mar 19, 2019
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Can anyone confirm whether or dot this will work with type 5 T-Slot extrusions, as well as the intended V-slot? It appears from the images that it doesn't have any parts that vit directly into the slit (other than T-nuts). Is that accurate?

Can be this used with Prusa MK2.5s Half Bear Upgrade?

No, unfortunately, I don't think it fits. If I remember correctly, the belt is placed at another height of MK2.5/MK2.5S.

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Yes you can. So have I done on my printer myself. Hope you like your Bear, I do :-)

i dont know why my comment was deleted, but thank you :)

I know i have asked about stock idler, im not sure if i have asked about bed mount.. does it hold firm? i like the design, but im worried about securing the belts, without any screw..

I think we now are over 100,000 owners of a Prusa printer, but I have never heard of anyone having problems with the belt holder.
So you don't have to worry about it. Are you a member of Prusa's forum?


yes im member, i didnt hear about anyone too, im just new to upgrades.. :D it is just direct upgrade - so it works with bear y motor mount (from last picture i assume)

will print this tensioner, thank you!

Does Anyone know if this y belt tensioner works with the i3 MK3S?


Yes it fits both MK3 and MK3S because they have the same Bear frame.

I'm getting belt deflection. Did I use the wrong y belt holder?

What belt holder do you use here? Is it the belt holder for MK2s/MK2.5?
If you want a completely parallel belt path, you can use my belt holder that I have now uploaded.

I am using the stock mk3 belt holder with the stock 20t idler

There must be something wrong here.
With the Prusa belt holder/tensioner R4, the belt would lean 1 mm down towards the belt holder, but your belt will tilt strongly up instead.
Is it an MK3 / MK3S you have?
Are you perhaps using the wrong bearing holders so that the bed is too high?

Standard mk3 with the full bear upgrade. Bearing holders are the mk3 version of the following. https://www.thingiverse.com/thing:2823171/files.

Prusa i3 Bear Bearing Holders

It may be the belt holder. I'm using either the R2 or R3

Yes there is probably the error. With Prusa Y-belt holder R2/R3 then the angle deviation becomes larger, so use my RHD-belt holder so the belt path becomes perfect.

Hi, is this for 16t or 20t idler?

Hi gentle_fister, it is intended for 20t idler.

Great! :)
Can it be used with any "standard" y-belt holder, or is it designed with a specific one in mind?

"Can it be used with any "standard" y-belt holder"

Yes you can, but Prusa belt holder provides a slightly angled belt path.
If you want a completely parallel belt path, you can use my y-belt holder that I have now uploaded.

You're an angel among men! Thank you!

Does this work on an i3 Mk2.5 also or is the belt alignment different?

It will fit on the frame, but unfortunately it differs 2.5 mm in height between the pulley shaft center.

Thank you for designing this. Wish this one showed up better in search. I was lucky enough to browse your other designs when downloading your fan shroud.

Thank you for enjoying my design.
I now see that I have missed "tagging" some things.
Thank you for the reminder :-)

If you do not want to dismantle the frame to move down the M5 T-nuts, it works well with the M3 T-nut drop in as well.
I already mounted these T-nuts when mounting my Bear upgrade.


T-nut M3 drop-in rotating 2020 V-Slot (Tevo, Creality, Tronxy, Anet)
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Well, that frame is really nice. I actually won it in a contest, bearcontest01.
If I am properly informed then the frame is available in 6 different colors.



Prusa i3 Bear Upgrade v2.0

Love the look of your bear upgrade and y tensioner. Did you anodize your purple extrusions yourself or buy them? I would love to know where you got them if purchased :)

Thank you pekcitron, for the screws so I'm talking about a well-built printer where the screws make that little extra :-)
But the best thing would be if the pulleys had a crowned pulley design.

very good design, like it (even if I am not totally sure about the two screws :-) )!

nice frame!
this is a nice design