For anyone that’s interested, this is what a failed steel belt looks like.
Shot of the toothed side:
And the back side - on the machine:
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My X is on the brink of destruction.
Plus, I’ve replaced my right side Y twice, left side zero.
Inconsistent quality is my guess. What does everybody else think?
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Given that they are so cheap, pretty sure there isn’t the best quality control. I’d prefer a Gates version in kevlar, but as far as I can tell, Gates doesn’t make them in that variation. I’ve used kevlar and steel. I put steel on my X axis, and kevlar on the Y to see how things held up. I’ve broken two steel belts over the past year, the kevlar is still doing fine. The steel doesn’t seem as durable as the kevlar, but stretches a little less (right up until it gives up 
) I think I prefer the kevlar.
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Where, on the length of the axis, did it break? I wonder if a section got bent past the bend tolerance during installation and made a weak point.
FWIW, I’m still rocking fiberglass-reinforced Gates belts from SDP/SI on the X and Y of my XL (they were out of endless loop when I ordered) — guess I should place another order.
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About ⅔ in from the left side. The part right at the clip has some distortion, but not broken.
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Can you give us a source on the Kevlar?
Only source that I’ve found, I actually just received another roll too shipping took about a week, go through the checkout to get an actual shipping cost, was ~$11 to Colorado.
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Address
Company: RepRapWorld B.V.
Address: Wagenmaker 6a
Zip code: 2631 RL
City: Nootdorp
Country: Netherlands
State: Zuid-Holland
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Are/were hard or soft limits being used to prevent crashing into the end stops? At two-thirds from the ends it sounds like no.
$11 is pretty good, I just checked and to Connecticut it’s $24.30 for any size. I was thinking I’d get 10 meters to have spare - total comes to $44.30
Do you know how many hours were on it before it broke? I just installed my steel core and might see if I can try to remember to log hours before belt failure. I think it would be great if we could get as many people as we can doing this for the steel core and the Kevlar ones so we can get a real world comparison going.
Get enough information and put together a cost over time for those unsure if the higher cost is worth it or not.
What size are you guys ordering? I’ve been thinking about getting some spare in case of a failure. What length for each side?
Thanks
Bulk roll, then cut to size. I order ~10 meters, which is enough to do the whole machine a number of times.
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I’m not sure that’s a great comparison in my case. I put about 30 hours of actual cutting time in over the last year, mostly wood, but some aluminum, brass and plastic.
I’ve got uprated steppers, was doing some work on the machine (new controller) and rammed it pretty hard into the left size rail a few times.
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“rammed it pretty hard into the left size rail a few times.”
Truth be told, probably most users are causing belt failures that way. Soft limits enabled would go a long way to lessen belt failures IMO.
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Yes, but soft limits have proven to be the cause of some really inscrutable support tickets.
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Given what I was doing at the time (setting up a new controller…things gone very awry…) it wouldn’t have helped 
I wonder with all of the looping through pulleys and such if the steel takes a permanent deformation and work hardens over time? Is there a minimum bend allowance type of rating for these? I’ve honestly never explored them. If you think of a paper clip you can use it to clip papers and it snaps back into shape. But if you bend it to the point of permanent deformation, it doesn’t. Do that enough times and it breaks. Just my $0.02
Dan
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Yes, there is a EDIT minimum (not maximum as @rowiac pointed out below) bend radius for the steel core belts, and the belt routing on an SO3 exceeds it — my assumption is the loads are low enough that it won’t be an issue — it’s a big push towards belts as consumable to my mind though.