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UMO+ : belt tensioners springs not documented

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though not mentioned in the documentation, 4 springs are provided with the UMO+ kit. they look like clothespin springs, and are intended to be used as belt tensioners.

they are indeed quite effective, as they provide dynamic tension, but also pretty difficult to assemble (some blood stains on my slider blocks).

i'm not really sure of how they should be mounted, but here is what i did, and it seems to fit quite well this way :

place them on the side on the belt that is not inserted in the sliding block, with the barrel on the smooth side of the belt, and the arms on the dented side.

be sure to place them so they dont touch the pulley when the slider block is in the opposite corner : you should place then symmetrically vs the corresponding block.

the easy way to know they are placed well is to either center the block and the spring, or to move the block to one side and put the spring on the other side, but though that makes it easy to know where to place the spring, it makes it harder to actually place it (less slack or less space available), so it's better to move the block off from the center, and to put the spring with same offset in the opposite direction.

check afterwards that they dont touch the pulleys when you move the block from one side to the other. if they do touch, you are allowed to cry a little bit, and then unmount them and try again.


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Hi I just got my UMO+ from Imakr (assembled) and they left me 2 bags with items. The 'timing belt spring 1681 x4' and other think.

Where exactly must I place it? Any photo for a bignoob like me?

Also. What is the 'Metal cable clamp 1514 x1'? And where does it go?

They forgot to put the calibration sticks that are used to align x/y so for now I can't print :D

Edit. Photo of the 2 little bags



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Ok I found the 'documentation' on that Timingbelt spring...

It's ofc, on somewhere else, on the Ultimaker 2 Assembly Manual

um2 assembly manual V1.1 _english.pdf

So I place them just outside like any other tensioner from youimagine or it's better to open everything?...

Btw if anyone can tell me where the Metal cable clamp goes...



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about the tentioners, on the UM+ there is no "inside" to the slider blocks, so you would need to put them on the outside of the belt just like any other tentioner printed from youmagine. I also use the microwave V2 model from here (they are great): https://www.youmagine.com/designs/microwave

about the cable clamp. I just put mine on the side to hold the heated bed cables as shown in this image:


I don't think it's super important to have that clamp...it's not in the assemble notes for the UM+

the sticks are nice, and hopefully they aligned it enough for you to use it for now. I never go sticks with my original and have been using these wonderfull things ever since:


oh and I noticed this too (never used it)



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Problem it's that the x/y are visually out of alignment on my ultimaker so I can't print yet. I'm gonna make this weekend a simple alignment tool with lego (got like 2 boxes of technics)

Great info on the clamp, didn't saw that photo, that does clear thinks up :D

That microwave tensioner seems kinda cool, and neat the idea to be able to place more in the future using very little space.

Thanks a bunch!


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I would align them as best as you can by eye.

Once you get it halfway kind of acceptable. Print some spacer sticks. Just make sure you print them all in the same exact orientation. As long as they are identical, it doesn't matter if they are both skewed a little. Then use those to properly align your printer.

BTW, it is much easier to align everything when the sticks have several positions. Otherwise you can wind up with the set screws where you can't tighten them.


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I've tried a few belt tensioners on my UMO over the last 2-1/2 years. I always come back to simple modified (bent) clothespin springs. I'd like to have a set of the newfangled official UM springs, because they have a nice and deep square shaped hook on them so they should stay put on the belts very well. Also, they don't require custom trial and error bending like clothespin springs.

The nice thing about the springs is they can be bent to supply the desired tension and then they will maintain it in "set and forget" mode for a very, very long time!.


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