Critical Revolutions per Minute of a Trapezoidal AccuLeadScrew Mechanism

The value of critical revolutions per minute is the speed at which a screw can rotate before high levels of vibration are caused. The critical revolutions per minute limit should never be reached, because the significant vibrations can cause operating irregularities and serious damage. Critical rpm depend on screw diameter, end constraints (bearings), free length "lg" and from the assembly accuracy.
For values shown in Graph 7 assume a minimum safety factor related to the assembly accuracy as per the following chart:

Chart No. 3 - Assembly accuracy coefficient

Assembly accuracy Conditions Safety coefficient
Good assembly accuracy:
- Nut alignment with screw less than 0.05mm Bearing and nut seats obtained from CNC lathe onto an already finished structure. 1.3 – 1.6
Average assembly accuracy:
- Nut alignment with screw less than 0.10mm Bearing and nut seats are processed on parts which are later assembled. Alignments are checked by comparators with extreme care after mounting. 1.7 – 2.5
Low assembly accuracy:
- Nut alignment with screw less than 0.25mm Bearing and nut seats processed on parts which are then assembled or welded together. Alignments are checked by comparators after mounting. 2.6 – 4.5

Graph No. 7 – Critical RPM

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