Straightening machines bring shafts and bars within specified straightness or rotational accuracy limits, enabling assembly or minimizing stock removal in subsequent machining. In the narrow sense, straightening corrects bending in rotating parts such as stepped gear shafts, armature shafts, splined shafts, piston rods, axle shafts, plain shafts, racks and drilling rods. The broader scope includes coiled stock, screws, threaded rods, drills, linear guides, polygonal or oval bars and irregular profiles. The archived article restricts its discussion to metals and attributes this to their combined ductility, toughness and plasticity; this generalization requires technical review.
Straightening equipment corrects bending introduced by rough machining or heat treatment in shafts, bars, screws, guide rails and rectangular drive racks used in automotive, marine, aerospace, drilling, textile machinery, motor and gearbox applications. It can reduce the stock allowance needed for subsequent machining or bring a part within final design tolerances. Automatic straightening develops this process beyond manual operation.