Broken belt

  • Hi!

    As I was having more and more strange results on my CoreXY, I started to change the way the belt is attached to the carriage, and realized it was broken 😞

    The glass fiber inside the belt broke, so the belt was not rigid anymore, and accelerations tended to increase its length, so my artifacts…

    I didn't see it before, as the broken part was on a idler pulley when carriage is homed...

    Anyway, it was a cheap chinese stuff. So, I'm now looking for a better one. Do you have suggestions? I would like to buy it from Europe, to be sure to get a decent quality. It is a 3GT, 9mm wide. Do you think I should go for a metal insert? Or is (good) glass fiber OK?


  • Not sure about Europe but in the USA I buy from I've never had any issues with their quality.

  • Thanks, but shipping cost will be too high…

  • I had good luck with belts from random German sellers on e-bay. One thing - I wouldn't really go for metal-core belts, they are far more vulnerable to being damaged by bending them too tightly…

  • Misumi sells belts that are compatible with Gates GT3, they are listed as MR2.

  • Thanks for these infos! I would have think metal core was better…

    I'll have a look at Misumi...

  • Metal cores are not good for our uses the cores work harden and eventually snap the best ones are either Aramid or Kevlar cores followed by Glass Fibre ones Misumi EU don't seem to list those belts in an open ended form

  • I'll go for Kevlar core, if price is ok.

  • @fma:


    As I was having more and more strange results on my CoreXY, I started to change the way the belt is attached to the carriage, and realized it was broken 😞

    . . . I'm now looking for a better one. Do you have suggestions?


    Hi There,

    I've seen SynchroMesh (SDP/SI) used in a cartesian style 3D printer, ( in place of belts. Its not too pricey as it is sold by-the-meter rather than by-the-foot. Its metal. See:


  • I would need to change all pulleys 😞

    About belt material, what is better : rubber, neoprene, polyurethane?

  • I just buy cheap GT2 belt from wherever I can find it. Never had a problem throwing 4 Kgs around - actually that's not true, it's around 2 Kgs per belt system. Oh and I've experimented with print speeds up to 300 mm/sec with that mass as well. Belts have never been an issue for me. Having said that, I consider them to be items that should be replaced every couple of years or so in any case (just like the cam belt on a car).

  • I found that PU belts seems to last long, but I can't find some 3GT-9, and they all have metal core 😞

    So, what difference between rubber belts, and neoprene belts? neoprene seems to be a synthetic rubber. But I wonder if the so-called rubber belts use natural rubber, or are they also made of neoprene?

    If PU is really better, I may switch to another ref, as long as they are 9/10mm width… I would only have to change the motor pulleys.

  • GT3 is a proprietary specification of the Gates corporation. It specifies fiberglass strands, neoprene backing, with nylon faced teeth. Anything else is not even trying to be GT3.

    GT2 is the exact same specification, but GT3 has changed a bit of the construction material in the backing itself. (I think making the neoprene or fiberglass thicker – it's proprietary, we don't know.)

    I would advise using neoprene backed belts, with fiberglass cord and nylon faced teeth. 🙂

  • Thanks! I didn't know GT3 was a complete spec; I thought it was only about teeth profile…

  • No problem. It took me years to discover that, as well. Most sellers are just supplying knock-offs. Some are licensed. Misumi's "MR2" line is licensed, while their "2GT" line is not.

  • Are you actually after 3 mm pitch belt? It does get confusing with the GT specifications (in which the number does not relate to the pitch).

    I would wager that the last one, at least, is licensed, because they mention the Powergrip trademark.

    I don't think you should worry TOO much about authenticity, unless you're designing a highly mission-critical machine for sensitive applications, where you have to be able to prove you used authentic parts for safety/regulatory reasons.

  • Yes, I need 3mm pitch belt (I already have pulleys, and all is designed for them).

    I just want to be sure to get a good belt, and I don't pay 15€/m for the same crap chinese guys sell for 2€/m!

    I noticed on my belt there are some parts with idlers print: they remain with an angle… I don't use my printer that much, and it often stays in the same position for days; looks like the belt didn't like it...

    BTW, how can I see what the core is made of?

  • I once bought steel reinforced belt from ali, and havent had any issue with it.

  • How long of a length do you need? Are you looking for closed loop belt, or an open length? I realize now that Misumi only sells closed loops, but you may be able to get the length you need and cut it.

    How long? And which country are you in?

  • I need 4m, in 1 piece… I already checked, and I never found a closed belt > 1m70. So, even if I use 2 belts, it is not enough.

    I'm in France.

  • Hmm, I see that the French misumi website doesn't even list the MR3 belt (Misumi uses the number to indicate belt pitch, unlike gates… confusingly).

    Perhaps you should buy several types of cheap belt from China, then you can choose the one that looks the best (You should be able to visually see the fiber core from the side or the cut ends).

    Pick the one that looks like it was cut the straightest, has no defects in the surface, has the most tensile members, etc.

  • Yes, GT3, 3GT GT 3MR… What a mess! In fact, I'm using old Stratasys parts, which where using GT (first gen, I guess). The Stratasys belts (Gates) are good, even after years.

    I'm waiting for Tanals answer, as they sell PowerGrip(R) GT and GT3.

  • Well, it sounds like if there are belts to be had in France, you will find them. Good luck!

  • Pfff, they don't want to sell to individuals 😞 Then they complain we buy in china… It puzzles me.

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