Critical Speed: Precision Ball Splines
The final factor to verify is the critical speed. The following formula is used to calculate critical speed in r.p.m.
|N =||Cs × 4.76 × 106 × d|
- N = Critical Speed (rpm)
- d = Root Diameter of Screw (inch)
- L = Length Between Bearing Supports (inch)
- Cs = 0.36 for one end fixed, one end free
- 1.00 for both ends simple
- 1.47 for one end fixed, one end simple
- 2.23 for both ends fixed
Critical speed can also be affected by shaft straightness and assembly alignment, it is recommended the maximum speed be limited to 80% of the calculated value.
To Use This Chart
- Determine the maximum RPM.
- Determine the maximum length between bearings.
- Determine end fixity.
- Find point at which length and speed intersect.
- Choose spline direction to the right or above the intersecting point.