Mendel Pulleys

by nophead, published

Mendel Pulleys by nophead Mar 28, 2010
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Mendel Pulleys by nophead is licensed under the GNU - GPL license.

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Mendel pulleys that use an M3 grub screw and a captive nut. The advantage over the original is that you only need one small flat on the motor shaft, rather than two full length ones that have to be filed to exactly the right size.

Can be used for all three axes.


Ream the holes out to 5mm and 3.5mm, fit the nut and grub screw. File a small flat on the motor shaft where the screw will engage.

I find it best to print three at the same time because it stops the small section getting too hot. If you have a machine that oozes then it may be best to print one at time to avoid strings.

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Looks a fantastic alternative to the horrible filing job that I am avoiding from days....

I tried to fit a M3 nut in the hole but it does not fit - shall I use something smaller or just force the nut?


M3 nuts fit when I print them, but they are deliberately a tight fit. Maybe your printer setting are making the holes smaller.

If it ABS you can open them up by scraping with a sharp penknife. You can also heat the nut to above the melting point of the plastic and force it in.

Many thanks for the advise - it worked! Just used the soldering iron 2 seconds.

I was wondering now about the timing belt - I got a 10mm wide 5mm pitch as this pulley is designed for that. Shall I cut it in half in order to have a 5mm wide belt? I cannot find another 5mm for sale with that pitch!

I am also wondering if the long pitch (compared to the "advised" 2.5mm or smal
ler for belts of that width) is a disadvantage for movement precision?
What do you think?

If you are making a Mendel than yes you need to use the belt splitter jig to cut it down to 5mm to fit the machine.

I think you get a little less backlash with a T2.5 belt because T5 doesn't bend as sharply round the pulleys but it is too fine to print pulleys for.

I'm trying to build a mini-Mendel / Huxley, which look simpler!

Do you have the file for a T2.5 pulley? I'd like to have a go at it... also if I read below that you use smaller nozzle/filament already!

Anyway,how exactly do I re-design it? Is it just making teeth half size and also closer together by half dimension, but keeping the external diameter untouched to not affect the ratio?

Thanks again.


Sorry no I don't have a file for a T2.5 pulley or know how to design one. The teeth on these came from the original Mendel files so they were designed at Bath.

I printed these with a 0.4mm nozzle so I would guess you can print T2.5 with a 0.2mm nozzle and get comparable results.

Worked great, and much easier to use than filing the motor shafts down! I drilled the central holes out so they were a press-fit on the stepper motor shafts, and didn't find it necessary to use a set screw.

NopHead, thanks for sharing! -- and that seems a good improvement to original ones from Mendel. I added a link to this ones as an alternative:


What size nozzle did you use and what were some of the other parameters for this print?

0.4mm nozzle extruding 0.375mm filament at 16 mm/s for the outlines and 32 mm/s for the infill. Layer height 0.3mm. ABS at 220C, bed at 120C for the first layer, 100C after that.

I concur with printing multiple small parts at the same time to avoid mushing a hot layer. I believe the new makerbot extruder firmwares have "de-ooze" built in.

Thank you! This is better then what I was planning to do with mine (drilling out the inside and drilling a small hole for a set screw/grub screw) - the addition of the nut makes perfect sense!

What length screw should be used?

Yes I tried tapping ABS and putting a grub screw into it bit it failed very quickly. I think tapping PLA would work better.

The grub screws I used are 6mm M3.

Thanks much for the quick response! I'll let you know how it works out.