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Prusa (Bear) MK3 / MK2S / MK2.5 Y-Axis Belt Holder and Tensioner

by uepsie Aug 26, 2018
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this is a nice idea! But I'm wondering. Compared to the original MK3 belt holder, in this one the lower belt is about 0.5mm lower, and the upper belt is about 2mm lower. Is there a reason for this?


Is somebody using this belt tensioner with that 20T idler mount https://www.thingiverse.com/thing:3309424 and can verify that the belt path is straight?

E3D 20T Idler compatible mount for Y-Axis on Prusa MK3 with Bear Upgrade

You haven't any problem if screw unscrew with vibrations ?

I was wondering the very same thing.

After about 1500h of prints I haven't noticed any loosening.

Could you make one with the belts at the correct level spacing (even) for those who use a 16 tooth idler?

Comments deleted.

I am building a Core XY and would like to incorporate this design in it. Would you share the CAD files please?

Hi Buj

I dropped you a private message

Well, this is not working for the MK3 at all. Its not only running into the frame on two sides, the belt is scratching on the underside and... ah well look at the attached pictures.

I can confirm the issue. I'm also having the belt slip while tightening/tensioning even with the cover on. (I managed to whittle off the corners on both sides to make it pass the frame). I downloaded it yesterday, Nov 21, 2018.

Printed using atomic filament PETG, same as I used on the bear extruder upgrades

When did you download it?

The day before I wrote the comment

Same problem here. For this to work the 20T idler would need to sit lower. But even then the 16T pulley on the motor leaves even less room between the belts. It's a great design - but seems not quite right yet.

I used the original files to get the dimensions right. It's working flawlessly at my mk3

Yeah, confirming that something's not quite right for the MK3. MK3 with stock R2 parts originally, upgraded to R3 Extruder. It's running against the frame. I wonder perhaps theres some MK3 variations that got rod holders that put the bed higher, or something that lowers/raises the clearance

How much clearance is there between the bottom of the carriage and belt for the MK3?

I haven't put together my Bear Upgrade yet, just printing the parts for it now. I've been taking measurements and been toying with designing a Y-Carriage with tensioner built in like you, but one of my issues is determining how much I can add to the height of the part before it starts rubbing.

The issue I'm seeing is that your part comes in at 27.8mm, but comparing to my measurements, that's too tall and would result in rubbing. The most I can do is 25.5mm before I risk the belt rubbing.

Hi Hotpocketdeath

the belt is indeed close to the bottom of the block but there's still ~1mm clearance

Not sure I understand the drawing. But to me it seems like there is not enough clearance. Especially when you get closer to the motor.

Very nice work! Thank you :-)