Broken Belt - replacement

So I was working on a massive project the other day on my SO3. Half way through the project one of the Y belt broke! The machine then went crazy and destroyed the project… No fun.

Anyways… what size belt does the SO3 use? Also interested in upgrading these belts for a thicker/wider belt. Anyone know if this has been done before?


Originally they were 6mm wide GT2 belts.

Since they were upgraded to 9mm wide.

I ordered my SO3 in October so it came with 6mm belts. Is there benefit to upgrading to 9mm?

I believe 6 -> 9mm wide belts is such a bang for the buck upgrade everyone should do it, and was surprised it wasn’t standard, and am pleased that it now is. The major advantage for Carbide3D is that it’s necessary at the larger sizes, so simplifies their kitting and parts ordering.

For everyone else:

  • 50% greater tensile strength
  • 50% better tooth engagement for less slipping

I was planning on doing before and after cuts, but a 6mm belt broke immediately before I could do that. I list the parts I ordered on my web page on the wiki.

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Thanks, Will! Sounds like a very smart upgrade. Do you know if I just need to replace the four belts, or if I also need larger belt clips and pullies? (I’m out of town so unfortunately can’t look at my SO3 anytime soon.) Also, I notice the wiki mentions X & Y but not Z. Does the Z belt need to stay 6mm?

On the wiki I see a link to this belt:
Or for half the cost at eBay?

For the pulley, I see you linked to both a 6mm version and a .25" version (which I assume is .3mm smaller). Do you know which one the stock SO3 should use?

Thanks as always.

The clips will work w/ 9mm wide belts. You’ll need new pulleys for X- and Y- axes — a wider belt won’t fit for the Z-axis, but weight / forces are low enough there it ought not be needed.

The specific parts I purchased are linked at: (all from SDP/SI) — I willingly paid extra to get pulleys and belting which if not Made in the U.S.A. were at least sourced from a reputable U.S. supplier. Planning on also doing spacers and reversing the Y-axis motors to match the X-, but haven’t found occasion yet. Probably when I get my XL upgrade.

I am going to order the 9mm belt. How many teeth does the pully need? What size bore?

Will this work?
Part Number: 26054-12

Also I am going to make a simple video of the upgrade for anyone else who might be interested in doing this upgrade. Going to also post the results. Any help would be greatly appreciated!

Bore is 6.35mm on most (all?) NEMA23 motors. 18 or 20 teeth should be fine — more would probably work, but would give up some positioning precision and low-end torque for greater speed.

As I noted, I bought my upgrade from SDP/SI — no experience ordering from other places.

Thanks Will!

Im not a big fan of ordering from sites Im not familiar with… But since you say you ordered it from them I will order from them if I cant seem to find what im looking for elsewhere. Thanks for all the help. I will be posting my results when i get the time.