1. Main screw not centered for upward movement. As the top moves closer to the center, where the top moves closer to the bottom (form) nut, the displacement of the top main screw makes it more angled from the centerline, and therefore the top movement cannot be moved safely. further towards the center, although there is a distance. Better stop the movement of the top in a safe place, not too close to the center, otherwise the top casting nut will be permanently damaged because the displacementβ¦