[Resolved] My belt broken many times in 10 days

I have new belt broken this day after two or tree times last week ago
I check all hardware and everything works great after awhile Ithe belt broken

upgrade the belt to 9MM.

That’s odd. How tight were they? If you email or call Inventables Tuesday they will send you replacements.

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Thanks Zach
I need to know why that happened many times
After tightening and calibration

Or, something is not aligned. check and recheck that the belts are not rubbing anywhere.

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As mentioned, make sure everything is properly aligned and your belts aren’t rubbing on any surfaces.

What are you setting your belts at? You are moving the gantry all the way to the fixed side of the belt before measuring the tension, right?

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@BillBlades I’ve been running my machine for years and I have never broken one belt. I wrote the manufacturer who said the belt will get softer if temperature reach and over 60C. The 6mm belt can withstand up to 500N, over that the belt stretch and break.

All this being said clearly his belt is broken so we need to understand what the issue is. It may be a defective section of belt or there may have been misalignment and rubbing.

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Yeah, never broken a belt either. Knock on wood. As mentioned, check everything.

Almost 3 years of use and no broken belts either.

The forum has been flooded lately with the broken belt problem. We figured you recently got a new supplier and there was a problem with the product. I too have run the original belts for 11/2 years.

Yea it might be a supplier issue. We need to investigate.

This needs to be answered. Even the best belt will break if set improperly.

That’s a huge assumption to make that it was assembled properly around here.

The new generation Xcarve removes a lot of questions with pressed on pulleys but the old ones required the operator to set the location of the stepper pulleys and there is a LOT of room for error there

Belts are meant for forces straight down their axis. Side loading is not part of the design. Now, make the stepper pulley be off axis from the smooth idlers. You’ve got additional side loading that the belt isn’t designed to take. It’s not so much the rubbing but the side loading that will cause issues. The rubbing is an indication that you’re out of alignment. The belt should be centered and stayed centered on the stepper pulleys.

I found this article relevant:



Thanks @BillBlades for the very detailed drawings. It was really thoughtful of you to help with that.

Thanks @JustinBusby good perspective there too.

I have emailed a few people internally to investigate further with the supplier. I’m also going to check to see if engineering can do some force testing. 500N is quite a bit in tension but as @JustinBusby noted it is weaker with axial loads.

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I work on my cnc 500 mm for four years without breaking the belt
After I updated to 1000 mm I have this issue and I check every things, belt tension is not clear and I follow videos but I think it might be some instructions for the belt in 1000 mm
Also is there any changes in gblr

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Belt is easy.

  1. Move the Xcarriage or entire gantry all the way to the FIXED end clip side of the axis.
  2. use a fish/luggage scale and pull the belt up 1” in the middle
  3. anywhere from 3.75 lbs at 1” to 4.25 lbs at 1” is acceptable. Either decrease or increase tensioning clip to get to the desired amount. Repeat measurement.
  4. done. For the Y axis, try to get both sides to match tension values. If left is 3.9 lbs, get the right to 3.9 lbs.
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While I hear a number of people in this discussion state they never broke a belt. A quick search will show you many many people breaking belts. I broke many belts, after the last one I and started the upgrade to 9mm belts. By started I mean, I’m still waiting on the 9mm GT3 belts to come from China. The only suppler I could find when I ordered a couple weeks ago. Everything else is ready to go.

Also follow @JustinBusby steps on setting the tension.

Most likely.

I’m sure there is a derivative calculation somehow that translate the deflection force at 1" lift over a 500mm span into belt tension but that’s not my cup of tea and why I went Electrical and not Mechanical Engineering :smile:

I’d probably use that as a basis and either half the downward force (so 1.875 to 2.125 lbs) or half the pull up (1/2" instead of 1") for a 500 mm machine. Assuming there’s a linear relationship. For the 750 mm, i’d reduce by a 1/4 and go either 3/4" pull-up or go 2.8 to 3.2 lbs at 1".

Again all assuming a linear 1:1 relationship between downward force and span length.

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when I purchase the new wide maker side there is no sign inventables on it so maybe i do not if i set it in the right way

Are you able to post some pictures of the ends of the set up?