Idlers tight over lapped belt area

I’m assembling an out-of-box 2019 Shapeoko 3 XL(standard z axis), it came with upgraded X and Y steel belts. When the gantry is pushed all the way to the back of the Y rails (by hand), the belt idlers encounter a large resistance when they meet the area of belt doubling about 2" of final travel.
I see a post by jjohnson sep '20: Idlers Tight with Belt, had same issue. The workaround was to reduce the belt doubling length to 1" to avoid the issue.

  • Are the steel belts thicker than the standard belts?
    Has the reduced belt lap length introduced any problems?

Yes, the steel belts are thicker.

Yes, some folks have trimmed them shorter to address this.

Please contact us at and we’ll send you a set of fiberglass belts.

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Thanks for the info and fiberglass belt option… For now I’ll adjust the lap distance.

Maybe check that the belt is laying with the teeth interlocked.
I still have steel cores and the doubled over belt is barely a bump. You can tell it’s there, but no problem to roll over.

Thanks, I really tried to ensure this when first installing the belts. Will double check when I re-do the lap distance. Is your machine a newer one with the zplus? I think the idlers(or positions) might have been changed to accomodate thicker belt sizes.

No, the hole positions haven’t changed since summer 2016.

Mine is a late 2019 model, stock belt driven z-axis

Ok, same as mine. Thanks.

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