Miniature rollnuts from Norco Inc., Ridgefield, Conn. (www.norcoinc.com), are designed for lab equipment and other applications which must smoothly and accurately insert and withdraw sensors, probes, or samples. A stainless-steel shaft rotating at a given speed generates uniform linear motion of the nut, but that can be changed to suit user needs. Long screw leads (up to four times the shaft diameter), let the nut move at relatively high speeds compared to the shaft turning speed.
The nut has centralized bearings at both ends, so it tolerates side loads and maintains alignment. The lifetime, lubricated ball bearings house a hardened ground-tapered roller. Backlash is less than 0.005 in., and there is little or no drag torque to overcome in turning the shaft. Mechanical efficiencies as high as 90% minimize the drive-motor size, reducing costs and energy usage. Screw diameters range from 0.13 to 0.38 in., nuts measure 0.75 to 1.5 in., maximum axial loads run from 5 to 20 lb, and maximum shaft speed is 2,000 rpm.