Yep,
There’s two constraints to consider here, the hollow pulley strength when not supported on the shaft due to overhang and the additional leverage that the belt tension forces have on the stepper shaft and bearings. Most steppers don’t expect to see large loads at any greater distance from the front bearing than the end of the shaft.
Will - I bought a maintenance kit June 26 this year and it has the steel belts. Installed the X axis in July but haven’t replaced the 2 Y axis belts yet. Would I still qualify to replace the Y belts with fiberglass?
Contact us at support@carbide3d.com — anyone who has steel belts is entitled to a replacement set of fiberglass.
@WillAdams, can I say that you and the Carbide3D team continually affirm my trust in you and the Shapeoko platform to be the tool I use for my little endeavor. Sometimes I doubt my choice and think I should have moved to a more expensive “pro” platform, but then you guys consistently support your products with EXCELLENT customer service and I’m put at ease. The first purchase I’ll be making when this stock of product is sold is a second machine (a pro this time) to expand my capacity. You guys are obviously VERY committed to us as your customers…and I, for one, really appreciate it.
I just received my xl-xxl upgrade last week, and haven’t had the time to check out the contents yet. Should the upgrade have fiberglass belts?
Yes, everything should be switched over to fiberglass — if you receive steel core go ahead and install them, but please let us know at support@carbide3d.com and we’ll send a replacement fiberglass set.
Is there a noticeable difference, so I can compare to the belts on my xl.
The steel core belts seem shinier and of course, at the ends one can see the couple of steel wires in them.
The fiberglass belts seem “grippier” and you can see strands of fiberglass along the edges due to how the are made.
Sounds great, one more question regarding the belts . I know that I will receive new belts why my " y " rails, is there also a new belt for my gantry “x” rail?
For the XL -> XXL upgrade I don’t believe a replacement X-axis belt is included — if you need one, let us know the circumstances at support@carbide3d.com and we’ll do our best to work through this with you.
Sounds like a plan 
Do the steel belts stick to a magnet?
Yes, insofar as narrow steel wires wrapped in a layer of rubber will.
What was the deciding factor in abandoning steel belts?
I had multiple belt failures 6 months in ( this summer). As usual carbide stepped up And got me up and running again with some new belts. I also ordered a roll of steel belts to have on hand now.
I’m assuming the steel belts don’t like the small radius bends that the machine ours them through.
What are the down sides of fiberglass vs steel?
I am very happy with my machines current capabilities 180ipm, .250” deep through Baltic birch with a 1/4” bit.
I’m curious to what changes will need to be made with the move to fiberglass belts. So they stretch more ect. With my current work flow I can’t afford much down time so I just have belts on hand waiting for the next breakage.
My understanding is high rate of premature failures due to the tight bend radius.
The steel advantages were:
Downsides for fiberglass:
I think most people where actually overtensioning the steel belts because they stretched so much less than fiberglass. Forum members tested this and it was a big number, something like 50% difference.
Something interesting to think about is that steel belt failures are pretty easy to see with a quick inspection. Fiberglass ones seem to go in stages.
It will be interesting to see how the pro performs with its 15mm belts.
I am looking for Nema 23 motors with a longer shaft so I can run 15mm or possibly 20mm belts but instead of the stepper nose bearing and shaft taking all the stress. I want to add a bearing block so the shaft is fully supported on both sides of the pulley. It would allow for wider belts, stronger steppers, and prevent snapped shafts while adding even more rigidity and possibly a longer motor life span.
The design pattern for this is to use a separate shaft with two bearings for the pulley and then use a shaft coupler to the stepper. There will be little choice in steppers with long shafts because that’s not how the mfr expects them to be used.
If you want to go up in radial load spec then the first thing is to go to 8mm or better shaft size.
Just curious, which method did you (@Vince.Fab) use to tension your belts? There are a few methods on the forum, so I wanted to see which you use.
Also, you mention a 6-8 months lifespan for your belts, how many hours is that? And do you notice more wear/breakage around the x-axis pulley in home position? Is your breakage always in the same location?
Sorry for all the questions Vince, I love your contributions to the forum, you (and others here) do awe-inspiring work!!
I base everything off feel and real world accuracy. Although I’m not against the higher tech techniques, imo the simpler the better.
Steel cores go 0-100 really quick, and I’ve only broken one set actually. Location seemed to be random. Given how much stiffer than fiberglass and the ability to be accurate without micro adjustments, its a no brainer. No ideas on total hours but my current set has over a year on them, plus long lengths of time fully tensioned.
Lots of talent and brain power on this forum for sure! Not just a bunch of button pushers 