Page 66 of Ball Screws by RBC Bearings

critical speed ­ rotational speed of a ball nut or ball screw shaft that produces a resonant vibration of the ball screw shaft deflection elastic deformation ­ the deformation of the ball screw assembly given an applied load deviation ­ an actual quantitative measurement that is other than specified dimension ­ specified quantitative measure and tolerance drag torque ­ the actual force measured at a radius of a ball screw assembly with or without wipers drive torque ­ the actual force including drag torque to actuate the ball screw assembly drunkenness ­ the characteristic of a ball screw assembly under load and rotation the plane at the interface deviates in both concentricity and perpendicularity dynamic axial load rating ­ the constant centric axial load that the ball screw can theoretically withstand for a basic rating life of one million revolutions efficiency ­ 90 ­ 95 for ball screws measured by the following criteria load stroke surface finish rpm lubrication end journal ­ the portion of the ball screw upon which is mounted the support bearings and is specified to conform to particular standards of concentricity parallelism perpendicularity and classified by grades equivalent load the mean load derived from the combination of varying loads that results in a life measured in terms of inches or cycles fatigue life ­ life of the ball screw assembly under the condition of a varying/reversing load measured in inches or cycles friction ­ the resistance to relative motion rolling or sliding between the ball nut ball bearings and screw shaft normally in the range of .0025 to .0035 for ball screws full radius ­ a ball track cross section of the ball nut or ball screw shaft whose opposing flanks are of similar radius and are measured from a common center gothic arch ogival ­ a ball track cross section of either the ball nut or ball screw shaft whose opposing flanks are of similar radius but offset from the center hardness ­ the property of substances determined by their ability to abrade or indent one another typically rockwell c or brinell measurement is used for obtaining a numerical value based on a metals resistance to permanent indentation heat treatment ­ the combination of heating and cooling operations applied to a metal or alloy in the solid state to obtain desired conditions or properties induction nitriding carburizing etc inertia of screw ­ half the product of the mass times the square of the screw radius land ­ area between two adjacent ball tracks on the screw shaft or ball nut lead ­ the axial distance between a point on a thread to the corresponding point on the next thread 66

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