3GT2 belting keeps breaking

This particular ebay store was the only place I could get an 8mm bore 3GT pulley back when I was looking for this.

While belts are history for me as far as tension I did the following till the very end with fantastic results for such a huge machine. The logic in what I used to do should apply to any type of a belt.

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Looks like a 5x11mm bearing, this one has a dynamic load number of 403 Newton, the MakerslideIdler wheel bearings are 5x16 with a dynamic load bearing of 1430 Newton.

Just try them out and see what happens. If the bearings fail you can always replace them with two 5x16 flanged bearings ike the SO3 does although they go even bigger. (F624ZZ)

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Sorry, the reference is for the 4mm shaft diameter, on ebay search for F625ZZ
You might just google in your area, many robot an print shops carry this bearing

Or just assemble a standard bearing, if your machine is properly aligned the belt will never hit the edges anyway

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Larger than what? The 625 2RS are identical to the Inventables bearings in Idler and Makerslide wheels. Idler seems based on the Makerslide Idler but with a center section of 5mm vs 1mm on the original one so they should be wide enough for the 9mm belts.

Rotary CNC? tell us more!

I was using openbuilds ones on my monster and I got to warn you that the collar on them is bit taller than xcarve.
I I had to sand off them a bit on X axis or they were riding on extrusion.

You can kinda see it on my old pic here:

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Go for it!


Yes was just a tinny bit, I was not even sure it first but that I seen them spinning when movie carriage without belts. If I remember right I just put then on a bolt and into a drill and ran them over sanding 3m block and was enough.

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Were those GT3 belts the 1536 loops? How’d it go cutting and trimming for the machine? Any real issues?

I put a long bolt through them and just pressed them against my disk sander. They spun quickly and ground down about a mm on each side very fast. It only took a minute to do them all.

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Have you considered 5/16" width Kevlar reinforced belts?

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Have you considered just replacing the belts with screws :grin:

The weak link in screws are the nut blocks and they cost $10 plus are adjustable till complete failure.

Nope… my machine crashed itself once and nothing happened. OK FINE! Twice but it wasn’t my fault, the machine was being naughty! :stuck_out_tongue_winking_eye:
ANYWHO when it “crashed itself” it reached the front y plates and bottomed out, the motors didnt have enough torque to damage anything. However with stock motors it only buzzed loudly and the nut blocks were ok.
With high torque motors you may strip a nutblock but i doubt it. They are super tough and durable.
I did crash a bit but it broke and nothing else happened. Not even lost steps. Rehomed and continued cut with new bit.

No damage.
And still no steps lost

My point is the weak point move to an easy to swap part that requires no tuning, and is very cheap and quick to replace.
Under 10 minutes if all goes well or 30min at worst.
The accuracy alone pays for itself.

What did you think about the Kevlar belts?

Talk dirty. Lemme hear the point.

Introducing a cost for a “disposable” item. Not great.

again. only a little. Ill tell you how i know. i left one motor unplugged and nothing really happened. again a loud buzz and not much else.
I do see your point. but the chance of single motor failure is minimal.