9mm GT2 Belts - Parts and Tools

Here is how I upgraded my belts to 9mm.


  • 9mm Belts - 12’ - Part 26053-02
  • 9mm Pulleys for NEMA 23 - Part 26054-12
  • 9mm Belt Clips x 6 - Custom Made - Easel Project
  • 9mm Idler Pulleys x 6
  • Existing Belt Clips and 8mm & 25mm M5 Bolts / Nuts from your X-Carve
  • 10mm Bolts x 4 - Part 25286-01
  • Aluminum Sheet 2.5mm or 0.1" works great. Thicker not required

Bits one can use to mill the aluminum:

  • I used this Dremel bit with my spindle at the lowest speed. Worked OK.

Final part, cleanedup, filed, and painted:

Used Easel’s default Aluminum settings with WD-40. Milling Time: 20 minutes each

Place the 25mm bolt into the original clip first.

Place the new clip on top, held down with 10mm bolts.

Loosely tighten the 10mm bolt.

Then use the 25mm bolts and tighten accordingly.

I went with this two part design, because bending the a new bracket seemed difficult without a proper metal brake. Plus I felt that the bend would be the weakest point as well. Luckily the old clip and new clip seemed to play well together.
You only need the old clip on one side of the belt.


I was thinking this would also be a good idea. What did you do for the idler wheels to allow for the wider belt? Thanks for info, looks great!

Whoops! I forgot to add those. I will update the original post

When I updated to 9mm belts several months ago, I just copied the design of the original 6mm belt clips. They work just fine with nothing more than a loop through the clip. Haven’t had a belt slip since!

Yes they are wider. Why else would I make custom ones? :smile:

1 Like

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.