Reprap Prusa i3 Rework - X END IDLER - With belt tensioner

by ramkam, published

Reprap Prusa i3 Rework - X END IDLER - With belt tensioner by ramkam Jul 13, 2014
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Mod of the X END IDLER. Added a tensioner for the X carriage belt.

  • installed it, it works.
  • Some suggested that using the other design with 3 bolts is needed for deformations and stress distribution on the z bearings. I didnt see that issue when i assemble it. Also i ran an FEM analysis, and i get the same outcome : it doesn't seem to be a concern.
  • Ran another FEM on the ball bearing holder ("roller puller"), it should be ok as long as you stay below 10Kg of tension force. Less than 2Kg force should be more than enough to get the belt tensioned, so, it's on the safe side and has provision for fatigue. Just print it with the same orientation than on the pictures of the assembled part, and slice it with 1.4mm wall thicknesses.


-- Assembly :
Print the X END IDLER and the Roller_Puller
Insert a screw in the roller puller, head of the screw goes in the socket (you may need to cleanup the hex socket a little, and to bend very gently the arms while pushing the screw head to its slot).
Insert the screw & roller puller into the X_END_IDLER bore, add a nut, et voila you have your belt tensionner
-- Careful:
The point in having this part is to be able to dose carefully how much tension you want to put. Dont tension the belt too much or you may endup putting too much stress on the tubes that contain your z axis roller bearings.
You may want to add a washer before the nut to even out stresses, and to use a nylock nut so that vibration during prints doesnt make it turn and go away.
-- Printing
I use a full metal extruder, so i printed with ABS at 240°C to get strong bonding (dont go that high if you have a JHEAD you'd destroy the peek)
Slicing done with Cura, with infill 30%, wall thicknesses 1.4mm top bottom 1mm. Seems to be rigid enough like that.
Printing done with the i3 at 30mm/s external sides, 50mm/s inner sides and 70mm/s infill, and extrusion rate at 110% to get some more chances of layers bonding.

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wont this still bend my Z ? as the rods are still free to move?

correct me if i am wrong

Sure does. How much though ;-) it works.

I like it a lot !
I have printed one but unfortunately cura didn't generate supports for upper part that hangs in air and final wasn't so nice.
What slicer have you used ?


Hi, what bearing size I use with this ? Thanks!!!!

Same as the original one or whatever has the closest match to the diameter of your pulley.
In the original build, it's 604ZZ.

Which screws need to secure the belt tensioner?

the screw the goes from the inside to the right (parallel to the rods). There's only one like this. It's a 4mm screw.

Hello, I have a question about this Idler, there's any chance that work with a 608zz bearing, or you have a parametric version of this idler?
Thanks in advance.

Oops, might have missed the mail notifications, sorry for the late reply.
Not sure it can fit nicely. The 608 is 7mm thick instead of 5mm for the 604; also, it's better that the bearing and the pulley (on the other side) have more or less the same diameters otherwise you'd get plenty of issues. So, no.
Regarding parametric, well, it could be interesting to trace the dependencies between the different components. Not sure it will model in the form of a tree, probably more of a graph. Would require lots of work. Is it worth it ?

I'm not sure if anyone was able to print it without enabling Support in Slic3r, but I think it's a must, otherwise top part (overhang) just collapses during print...

Hi bratan, you need to use supports for this one

Thanks! Yeah it printed fine with support. Now I'm having problem printing pulley (top of each ear "melts") but that's just issue I had with my i3 for a while :)

The overhang of the ears is small, it should go ok. try slowing down the print speed, it will give more time for the filament to cool down and give better results. Also, the ears are just there to prevent the bearing from sliding sideways, it's not important to have it perfectly printed. The arms on the other side will take some efforts, so print them well and slow

Yeah overhang there is not an issue. I think you are absolutely right about speed tho, I also suspected something like this especially since I increased edge printing speed recently... Thanks again! :)

Comments deleted.

Please, you can make X-END-MOTOR for m6 studs and nuts , or where i can find a model for editing ?

Hi Mobsman, the parts in scad format are here http://reprap.org/wiki/Prusa_i3_Build_Manual#EiNSTeiN_VARIANT and you may find variants and stl files by searching prusa i3 on thingiverse. Regarding the model, i only have made mods to the idler.