Critical Speed Using Nook EZZE MOUNTS

Using Nook Industries Compact Universal Support mounts is a convenient and cost-effective way to support a ball screw. Several configurations are available and designed to provide the proper axial and radial support needed for most linear motion applications. Nook Industries offers both a single bearing and multiple bearing arrangement.

Below is a depiction of various bearing arrangements and graphs to assist in determining the proper screw size based on column strength and critical speed.

Critical Speed Chart

This critical speed chart is provided to quickly determine the minimum screw size applicable for Nook EZZE-MOUNT™ designs. Maximum travel rate is also limited by ball velocity. The ball velocity is a function of the ball circle diameter and rotational speed. Critical speed of the nut is limited by a maximum DN (ball circle diameter × rpm). The charts show the maximum speed based on the DN value for each screw in parentheses.

If the selected ball screw does not meet the speed criteria, consider the following options:

  • Increase screw lead (reduce rpm)
  • Change end fixity (e.g. simple to fixed)
  • Increase ball circle diameter

The final consideration should be to recheck the selected screw against all three of the design criteria: life, column strength and critical speed.

To Use This Chart:

Determine maximum travel rate required. Determine screw length L. Find point at which travel rate and screw length intersect and select a screw above and to the right of that point.

NOTES:

  • Speed indicated by curves are 80% of theoretical critical speed.)
  • Maximum recommended speed (as limited by DN = 70,000, regardless of screw length) is indicated in parenthesis after each curve's screw size label.)
  • Number in parenthesis is the maximum speed in millimeters per minute based on DN= 70,000. )
  • Chart below assumes earth gravity at sea level.
    • For critical speed values on Nook miniature ball screws, contact Nook Engineering.

      Figure 1