Techno Linear Motion Catalog13Technical InformationThe Torque required should be well below the torque rating of the motor chosen. A modestfactor of safety should be added to the torque required so that unexpected dynamic loads aresafely handled by the driving system.Selecting and Sizing Screw Drive Systems: When choosing a particular screw for a given application,there are several factors to be considered. Required rpm, critical speed and maximum compressive strengthare the most important design features that determine screw design parameters, and can be calculatedaccording to the following equations. Since thread style design is irrelevant in these calculations, the sameequations and charts can be used for both lead screws and ball screws. Bearing configuration must beconsidered when using these equations. The following diagrams represent the typical bearing end supportarrangements.linear velocity (in/min)rpm = (4)lead (in/rev)The formulas above can be represented graphically by the charts on following pages. These charts havebeen compiled for screws made of stainless steel. Speeds, loads, diameters, bearing arrangements andproducts are referenced. It must be realized that a screw may be able to rotate at very high rpms, but thenut may have more strict limitations. For this reason, we have truncated the ball screw rpm diagrams to atop end of 4000 rpm, and provided each type screw with their own charts. Please note that the ball screwcharts are only represented for screws of 16 mm and 25 mm diameter.Maximum Speed:CS= F (4.76 x 106) (5)where:CS= critical speed (rpm)d= root diameter of screw (inches)L= length between supports (inches)F= end support factor (see diagram)case A.: 0.36case B.: 1.00case C.: 1.47case D.: 2.23Maximum LoadP=F(14.03 x 106) (6)where:P= maximum load (lbs) (critical load)d= root diameter of screw (inches)L= maximum distance between nut and loadcarrying bearingF= end support factor (see diagram)case A.: 0.25case B.: 1.00case C.: 2.00case D.: 4.00d4L2dL2NOTE:A.Fixed-FreeB.Simple-SimpleC.Fixed-SimpleD.Fixed-Fixed