Screw straightness refers to the degree of radial deviation exhibited by a lead screw during rotation. Higher straightness accuracy ensures smoother and more stable screw-driven motion. Straightness accuracy is closely related to the overall length of the screw. The industry-standard straightness tolerances commonly referenced are as follows:
- For a screw length of ≤100 mm: within 0.08 mm at the shaft end and within 0.03 mm at the root;
- For a screw length of ≤200 mm: within 0.10 mm at the shaft end, 0.05 mm at the mid-shaft, and within 0.03 mm at the root;
- For a screw length of ≤300 mm: within 0.15 mm at the shaft end, 0.07 mm at the mid-shaft, and within 0.03 mm at the root.
By extrapolation, for every additional 100 mm of screw length, the straightness tolerance at the shaft end increases by approximately 0.1 mm.
This demonstrates that as screw length increases, the straightness accuracy at the shaft end decreases, resulting in greater radial deviation during operation. Therefore, when selecting a linear motor with a long lead screw, it is recommended to add end support. End support serves two purposes: it helps prevent the screw from bending under load and reduces excessive radial deviation during rotation.
Note: There is no difference in straightness standards between trapezoidal screws and ball screws. Both types follow the same straightness specifications outlined above.