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Modified y idler pulley

Posted by alkempster 
Modified y idler pulley
October 26, 2015 02:26PM
I really like nopheads design and its implementation. However, i kept having trouble keeping tension on the y axis timing belt. Not really wanting to drill a load of new holes i set about creating a modified y idler and created:


This idler is a two part design the axle part uses most of the original design but removes the nut trap and adds two wings with M4 captive nuts. These are connected to the rear assembly which clips over the back base sheet. The use of two screws allows for the belt to be aligned on the pulley without hitting the sides by adjusting one or the other once tensioned. I nabbed the screws from the x carriage fan duct assembly (changed to an E3D-V6 so no longer fits), these are a bit short but i lengthened the belt to get it to work.

here is a before (purple) and after (black) test cube:


I am quite pleased with the improvement in print quality but i already have some redesigning to do:
- extend bolts or increase the size of the rear part and or captive nuts
- shrink the excess width (almost fouls the bar clamp)
- put a slightly larger gap for the pully skewer
- fix bottom sheet width

If you are interested, you can find this design at: [github.com]
(currently only fits the dibond build sold by nophead)

I own a mendel 90 and sell items on my website at www.computingunlocked.co.uk
Re: Modified y idler pulley
October 27, 2015 04:55AM
Feel free to join our group on Thingiverse to share mods and enhancements for our favourite printer! smileys with beer
Re: Modified y idler pulley
October 27, 2015 07:43AM
Not sure why you would need to keep tightening it, or drill more holes. The belt shouldn't stretch over time. I only tension mine once and then forget about it.

Re: Modified y idler pulley
October 27, 2015 07:50AM

I found, when I recently refurbished my printer and switched to GT2 belts and pulleys, that the original belt setup placed the tensioner too far back in the adjustment slot. I shortened the new belt and brought the tensioner further forward allowing a greater adjustment range. Perhaps this is what others have been seeing and leads them to alternative tensioner designs. I agree it should be set-and-forget.

Neil Darlow

I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.
Re: Modified y idler pulley
October 27, 2015 12:16PM
hi nophead,

i believe it should be set and forget. I couldnt tighten the base bolt enough without damaging the dibond sheet, i think this caused the pulley to loose tension over time. The modified design gets around this by not needing to compress the sheet to get a good grip and without having to drill new holes to support the modification. How tight do you bolt yours to the frame?


My printer is set up with GT2.5 belts, this put the original pulley about half way down the slot when tensioned, after a days worth of printing this would drop to an 1/8th off the short end of the slot.


thanks for the link, i didn't know that was there!
Re: Modified y idler pulley
October 27, 2015 05:32PM
I pull it back as hard as I can with two fingers and a thumb and then tighten it enough to not slip back. Then I rotate it so the belt runs in the centre of the idler and tighten it a bit more. Yes the washer will dig into the Dibond, but as it is underneath I don't class it as damage.

I don't find timing belts stretching over time so I can't explain why you would need to tighten it again further back. I run my machines for years without touching the idler setting. If the belt stretched then its pitch would change and the calibration would change. GT2 has Kevlar wires to stop it stretching.

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