Z Axis Plate idler pulley & belt problem Shapeoko XL

<img src="/uploads/default/original/2X/f/fead0e36275df082e084d5134f60bce298d2ba0f.jpg" width=“640” height="427"
I have had my Shapeoko XL for about two months and all has been well. I was running a job this afternoon when it became apparent the Z Axis Plate became frozen in place. When I disassembled the mechanism I discovered one of the two set screws on the idler pulley had vibrated loose (see picture) and jammed the gear from turning, making a loud clicking sound (not a belt skipping sound). It appears that the set screw had little or no LocTite on the thread.

  1. Can someone please explain the function of those set screws. If you tighten them down, they lock the pulley against the mounting bolt also preventing it from turning.
  2. Now even more curious, the belt will not bypass itself because the bushings appear to be pinching the belt too tightly together. I don’t have a clue why this is since it is threaded exactly as the instructions indicate and it was working well before this incident…
  3. Also, the loose set screw scored the vertical track on the left side. I was able to smooth it out somewhat with steel wool, but hopefully the factory can send me a replacement.
    Your thoughts and suggestions on issues 1 & 2 would be greatly appreciated.
    Thank you!
    Don Sieburg

It’s the static pulley being essentially fixed to the belt which allows the Z-axis motor to raise and lower the plate.

Contact support@carbide3d.com for a replacement.

Why is the belt binding on itself now… it does not allow the belt to move and prevents the pulley from turning. The two bushings adjacent to the pulley are too close together.

Because if the belt would move around that pulley, then it would spin, and the plate would stay in place — it’s only the belt gripping the static pulley and being resistant to moving around it which allows the motor to move the Z-axis spindle carriage plate.

Try it. Remove and loosen everything, then rotate the motor pulley and watch the belt rotate around everything, while everything but the idler pulley and the no-longer static pulley stay put, and those parts and the belt merely rotate / circulate, then pinch the belt tight around the static pulley and hold it so it doesn’t rotate, and then the plate will want to move.

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AHHHH… that makes sense now.