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Screws

Going all the way back to Archimedes screw (used to lift water), screw threads on a shaft have been used to change rotary motion to linear.

Basic parameters of screws include: Lead angle, lead, pitch angle, pitch, threads per mm or inch, grades of accuracy, load capacity.

  • ACME screws (or the European trapezoidal) are common on machines. Lower accuracy, with a large friction loss (40%+ in some cases), they cannot (generally) be backdriven by the load
  • Ballscrews have significantly lowered friction and hence raised efficiency (usually in the range of 90%+), but can have lowered load capacity. Can be easily backdriven