9mm GT2 Belts - Parts and Tools

what the advantage to using wider belts? please let me know

I used Lumicite - acrylic embedded with fiberglass. Made them the same length as the 6mm and 3mm wider.

Nope. I built a Shapeoko 2 early last year, so it had SO2 parts.

I also loop my belts different from the instructions.

Doing them like this helps ensure they don’t slip.

Looks good! I think when I get around to the upgrade, I’ll laser some out of Delrin. :smile:

Let the teeth do the holding.

This is 1.5x more meat per tooth.

I went with 6mm-wide GT3 (aka 3mm pitch GT2) from Openbuilds, which offers


…that is 2.35x more meat per tooth compared to 6mm-wide GT2 and according to them:

“great for use with Nema 23 size motors where deep tooth engagement is a necessity”


PS. Changing pitch also means that $100 & $101 values change from
(200step/rev * 8microstep/step) / (20teeth/rev * 2mm/tooth) = 40microstep/mm
(200step/rev * 8microstep/step) / (20teeth/rev * 3mm/tooth) = 26.666666667microstep/mm

(assuming 1/8 ustepping & 20t pulleys)

Multiple options and ideas is what makes open platforms like the Shapeoko and X-Carve so awesome!


So I am curious if you change the belt size will you still be able to use easel and the tinyg controller because of this:

PS. Changing pitch also means that $100 & $101 values change from
(200step/rev * 8microstep/step) / (20teeth/rev * 2mm/tooth) = 40microstep/mm
(200step/rev * 8microstep/step) / (20teeth/rev * 3mm/tooth) = 26.666666667microstep/mm

(assuming 1/8 ustepping & 20t pulleys)

I really dont know anything about this lol

If you upgrade

from GT2 2mm-pitch 6mm-width
to GT2 2mm-pitch 9mm-width

you do not need to change any configuration in GRBL. The pitch remains the same and therefore the microsteps required per mm do not change.

However, If you upgrade
from GT2 2mm-pitch 6mm-width
to GT2 3mm-pitch 6mm-width (aka GT3)

since the pitch (distance between the “summit” of two neighboring teeth) changes, the linear motion produced per microstep changes too and you need to account for it. The GRBL parameters that define microsteps/mm for X and Y axis are $100 & $101 respectively. They can be set via Easel or any other GRBL g-code sender (or a terminal talking directly to the Arduino).

If you forget to do so, the 50% increase in pitch will result in cuts 50% bigger than expected in both X and Y.

PS. I am unfamiliar with the TinyG configuration (or Mach3 or LinuxCNC for that matter), but in every controller there is a way to set the mictosteps/mm per axis. Again, this is only needed only in case of pitch change (GT2->GT3).

I have actually upgraded to XL (5.08mm) pitch, 6mm wide belts for my NEMA23 steppers. I’m fairly sure I will get minimal slippage/skipping. I’m working on milling a reverse mount for my NEMA23 Z stepper.

So… I ordered the GT3 pulleys and belts from OpenBuilds, they just showed up, the GT3 pulleys wont fit on the nema 23 motor shaft.

The GT3 pulley was the only one they had… what am I missing …?

As long as it is 1/4 bore they should fit.

The pulleys that came with the XC appear to be 8mm bore, the GT3 pulleys I got from OpenBuilds are 6mm bore, so they won’t work on the XC nema 23s…

Now to send them back and find someplace that has 8mm bore. Drat! I was hoping to get them installed this weekend.

This is strange. Openbuilds GT3 pulley’s inner dia should be 6.35mm (1/4") and so should Inventables NEMA23’s shaft dia. Mine fit fine.

Are you using calipers to measure both?

Yep, not metric calipers but …

0.243 inches (6mm) inner bore size on the OpenBuilds pulleys, 0.314 inches (8mm) inner bore size on the default XC pulleys.

OB pulleys are 2mm smaller, cant fit them on the steppers.

It is stupid to ask again, since your pulleys were mated to them, but your NEMA23 shaft also measures 8mm?

I thought that Inventables only stocked 1/4" shaft NEMA23s. It seems you were (un)lucky to be part of a non-1/4" batch.

Try contacting them directly to see if they would replace or trade-in the 8mm ones with 1/4" ones.

I’ll check again at lunchtime.

I grabbed the new OB pulleys this AM, walked out to the garage, tried to stick the new pulley on the Nema23, found it was too small, said some bad words, put both the XC pulley and the new pulley in my pocket and grabbed a caliper here at work.

Not sure what’s happening, but maybe I just need a hammer :smile:

@AngusMcleod was 100% correct.

The pulley I grabbed was the one for the Z axis ACME, and not for the stepper, so I was measuring the bore of the wrong pulley from the XC parts…

Crisis averted !

Thanks Angus!

lol well done …

About to jump into my own X carve build and already ordered the 9mm belts, idlers pulleys etc. Anyone identified a source for 9mm clips, or a resource that will fabricate them (or have any extras laying around?) :smile: