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GT2 Belts and Pulleys teeth count?

Posted by Phizinza 
GT2 Belts and Pulleys teeth count?
March 16, 2012 04:07AM
I have found a source for GT belts in Australia. But the pulleys are super expensive. An alternative is to get pulley bar stock. So I can get enough stock to cut myself enough pulleys for the same price as a single aluminium pulley.

The question is what amount of teeth should I get for the pulleys? I have option to get 10 teeth to 40 teeth. I read on the wiki page explaining why GT2 belts are better saying 12 teeth minimum but then it also said the less the better? So what amount of teeth should I get?

Re: GT2 Belts and Pulleys teeth count?
March 16, 2012 02:39PM
I don't know why it would say 12 is the minimum, unless that was the smallest pulley the author could find at the time. That's what I'm finding after a quick search at SDP-SI. The same place shows the 10-tooth stock. They're not going to sell pulley stock with a tighter radius than the belt can bend, so I'd go with the 10 and get a little more force and precision.
Re: GT2 Belts and Pulleys teeth count?
March 16, 2012 09:16PM
I think I just figured it out. the 12 tooth pulley has an outside diameter of about 7.64mm and because the teeth of 0.76mm high that gives a diameter between bottom of teeth of about 6.12mm. The Nema 17 motor has a 5mm shaft size.
The 10 tooth pulley has a diameter between bottom of teeth of about 4.85mm, therefor you couldn't drill the hole for the Nema 17's shaft.
I'm a bit worried even a 12 tooth pulley wouldn't be too strong, mainly while machining it, because the thickness of the body will be a minimum of 0.551mm.
Re: GT2 Belts and Pulleys teeth count?
March 16, 2012 11:28PM
That sounds about right, the shaft vs bore thing.

The 12-tooth GT2 pulley is actually what I use, and it does the job admirably. I wouldn't want to make the center bore without proper tools though (lathe, etc.).
Re: GT2 Belts and Pulleys teeth count?
March 19, 2012 02:03AM
You could put your nema 17 stepper motor on a lathe if you have one and turn the shaft to be a thinner diameter. I think you should probably get away with 4mm. 3mm would probably be the bare minimum you would want for your shaft.

This is all of course if you can gain access to a lathe...
Re: GT2 Belts and Pulleys teeth count?
May 25, 2012 04:02PM
Use MXL belting, much cheaper than GT2 and nearly the same tooth profile and pitch as well as it being designed for dual direction transitions, unlike T5 or T2.5. You can also get a 10 tooth pulley for MXL for a 5mm shaft from SDP/SI.
Re: GT2 Belts and Pulleys teeth count?
December 12, 2014 11:58AM
I'm working with a printer with a 12 tooth gt2 (2mm) pulley and I'm doing the ustep/mm calcs.
Isn't the fact that the teeth are a multiple of 3 a problem?
My calibration values are: 400steps*32usteps/12teeth/2mm(per tooth) = 533.333... usteps/mm
This means it's 533 and 1/3 usteps/mm or 16.666... full steps, wont we lose those decimals eventually leading to error?

My logic behind this is the problem with using anything but full (or half) full step resolution for z.
I realize part of the motivation for this is because the z is often disengaged while not in use and will fall back+/- 1/2 step.

I was looking for a 10 tooth pulley, but Phizinza, your calculations make sense.
My rough solidworks sketches made it seem like it could work, but it looks doubtful.
I got some gt2 16 tooth pulleys to give me a round number (400/16/2=12.5 steps/mm, 400usteps/mm = 80um/step, 2.5um/ustep)
The old 12 tooth pulley got 60um/step or 1.875um/ustep
I don't think I mind the slight loss in resolution to have nice round numbers (and no error?)

More important is my Z, its 400steps/12teeth*36teeth (geared down)/5mm (lead screw pitch) = 240 steps/mm
This is convenient because thats 4.1666...um/step and 25um/6steps
However, I'm converting the gear ratio to 2.5 to give 200steps/mm and 5um/step (lower than 4.1666..., but not a factor of 1/3)
On my old prusa i've got 200*16/(25.4/18) (5/16-18 rod) = 2267.71653543307usteps/mm, ...141.7322834645669 steps/mm
I try and do multiples of the full step length 1/141.7322834645669=0.0070555... or every 9 steps = 0.0635, its pretty usable, I usually go with 0.1905 or 0.2540.

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