Indexing in reference to motion is moving (or being moved) into a new position or location quickly and easily but also precisely. When indexing a machine part, its new location is known to within a few hundredths of a millimeter (thousandths of an inch), or often even to within a few thousandths of a millimeter (ten-thousandths of an inch), despite the fact that no elaborate measuring or layout was needed to establish that location. In reference to multi-edgecutting inserts, indexing is the process of exposing a new cutting edge for use. Indexing is a necessary kind of motion in many areas ofmechanical engineering andmachining. An object thatindexes, or can beindexed, is said to beindexable.
Usually when the wordindexing is used, it refers specifically torotation. That is, indexing is most often the quick and easy but precise rotation of a machine part through a certain known number ofdegrees. For example,Machinery's Handbook, 25th edition, in its section on milling machine indexing,[1] says, "Positioning a workpiece at a precise angle or interval of rotation for a machining operation is called indexing."[2] In addition to that most classic sense of the word, the swapping of one part for another, or other controlled movements, are also sometimes referred to asindexing, even if rotation is not the focus.
There are various examples of indexing that laypersons (non-engineers and non-machinists) can find in everyday life. These motions are not always called by the nameindexing, but the idea is essentially similar:
Indexing is vital inmanufacturing, especiallymass production, where a well-defined cycle of motions must be repeated quickly and easily—but precisely—for eachinterchangeable part that is made. Without indexing capability, all manufacturing would have to be done on a craft basis, and interchangeable parts would have very highunit cost because of the time and skill needed to produce each unit. In fact, the evolution of modern technologies depended on the shift in methods from crafts (in which toolpath is controlled via operator skill) to indexing-capable toolpath control. A prime example of this theme was the development of theturret lathe, whose turret indexes tool positions, one after another, to allow successive tools to move into place, take precisely placed cuts, then make way for the next tool.
Indexing capability is provided in two fundamental ways: with or withoutInformation technology (IT).
Non-IT-assisted physical guidance was the first means of providing indexing capability, via purely mechanical means. It allowed theIndustrial Revolution to progress into theMachine Age. It is achieved byjigs,fixtures, and machine tool parts and accessories, which control toolpath by the very nature of their shape, physically limiting the path for motion. Some archetypal examples, developed to perfection before the advent of the IT era, aredrill jigs, the turrets on manualturret lathes,indexing heads for manualmilling machines,rotary tables, and various indexing fixtures and blocks that are simpler and less expensive than indexing heads, and serve quite well for most indexing needs in small shops.[3] Although indexing heads of the pre-CNC era are now mostly obsolete in commercial manufacturing, the principle of purely mechanical indexing is still a vital part of current technology, in concert with IT, even as it has been extended to newer uses, such as the indexing of CNC milling machine toolholders or of indexable cutter inserts, whose precisely controlled size and shape allows them to be rotated or replaced quickly and easily without changing overall tool geometry.
IT-assisted physical guidance (for example, viaNC,CNC, orrobotics) has been developed since theWorld War II era and uses electromechanical and electrohydraulicservomechanisms to translate digital information into position control. These systems also ultimately physically limit the path for motion, as jigs and other purely mechanical means do; but they do it not simply through their own shape, but rather using changeable information.
