Indexing (motion)
Encyclopedia
Indexing in reference to motion is moving (or being moved) into a new position or location quickly and easily but also precisely. After a machine part has been indexed, its 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. Indexing is a necessary kind of motion in many areas of mechanical engineering
and machining
. A part that indexes, or can be indexed, is said to be indexable.
Usually when the word indexing is used, it refers specifically to rotation
. That is, indexing is most often the quick and easy but precise rotation of a machine part through a certain known number of degrees
. For example, Machinery's Handbook
, 25th edition, in its section on milling machine indexing, says, "Positioning a workpiece at a precise angle or interval of rotation for a machining operation is called indexing." 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 as indexing, even if rotation is not the focus.
, especially mass production
, where a well-defined cycle of motions must be repeated quickly and easily—but precisely—for each interchangeable part
that is made. Without indexing capability, all manufacturing would have to be done on a craft basis, and interchangeable parts would have very high unit 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.
.
to progress into the Machine Age
. It is achieved by jigs
, 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, are drill jigs, the turrets on manual turret lathe
s, indexing head
s for manual milling machine
s, rotary table
s, 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. 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.
, CNC, or robotics
) has been developed since the World War II
era and uses electromechanical and electrohydraulic servomechanism
s 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.
Mechanical engineering
Mechanical engineering is a discipline of engineering that applies the principles of physics and materials science for analysis, design, manufacturing, and maintenance of mechanical systems. It is the branch of engineering that involves the production and usage of heat and mechanical power for the...
and machining
Machining
Conventional machining is a form of subtractive manufacturing, in which a collection of material-working processes utilizing power-driven machine tools, such as saws, lathes, milling machines, and drill presses, are used with a sharp cutting tool to physical remove material to achieve a desired...
. A part that indexes, or can be indexed, is said to be indexable.
Usually when the word indexing is used, it refers specifically to rotation
Rotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...
. That is, indexing is most often the quick and easy but precise rotation of a machine part through a certain known number of degrees
Degree (angle)
A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...
. For example, Machinery's Handbook
Machinery's Handbook
Machinery's Handbook for machine shop and drafting-room; a reference book on machine design and shop practice for the mechanical engineer, draftsman, toolmaker, and machinist is a classic reference work in mechanical engineering and practical workshop mechanics in one volume published by...
, 25th edition, in its section on milling machine indexing, says, "Positioning a workpiece at a precise angle or interval of rotation for a machining operation is called indexing." 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 as indexing, even if rotation is not the focus.
Examples from everyday life
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 name indexing, but the idea is essentially similar:- The motion of pins inside a pin tumbler lockPin tumbler lockThe pin tumbler lock is a lock mechanism that uses pins of varying lengths to prevent the lock from opening without the correct key...
, which the correct key can move quickly and easily but also rather precisely into the correct position to allow the lock's cylinder to turn - Indexable driver bits for screwdriverScrewdriverA screwdriver is a tool for driving screws and often rotating other machine elements with the mating drive system. The screwdriver is made up of a head or tip, which engages with a screw, a mechanism to apply torque by rotating the tip, and some way to position and support the screwdriver...
s - The motion of a retractable utility knifeUtility knifeA utility knife is a knife used for general or utility purposes. The utility knife was originally a fixed blade knife with a cutting edge suitable for general work such as cutting hides and cordage, scraping hides, butchering animals, cleaning fish, and other tasks.Today, the term "utility knife"...
blade, which often will have well-defined discrete positions (fully retracted, ¼-exposed, ½-exposed, ¾-exposed, fully exposed) - The indexing of a revolverRevolverA revolver is a repeating firearm that has a cylinder containing multiple chambers and at least one barrel for firing. The first revolver ever made was built by Elisha Collier in 1818. The percussion cap revolver was invented by Samuel Colt in 1836. This weapon became known as the Colt Paterson...
's cylinderCylinder (firearms)In firearms terminology, the Cylinder refers to the cylindrical, rotating part of a revolver containing multiple cartridge chambers. The cylinder revolves around a central axis in the revolver to bring each individual chamber into alignment with the barrel for firing...
with each shot
Manufacturing applications
Indexing is vital in manufacturingManufacturing
Manufacturing is the use of machines, tools and labor to produce goods for use or sale. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale...
, especially mass production
Mass production
Mass production is the production of large amounts of standardized products, including and especially on assembly lines...
, where a well-defined cycle of motions must be repeated quickly and easily—but precisely—for each interchangeable part
Interchangeable parts
Interchangeable parts are parts that are, for practical purposes, identical. They are made to specifications that ensure that they are so nearly identical that they will fit into any device of the same type. One such part can freely replace another, without any custom fitting...
that is made. Without indexing capability, all manufacturing would have to be done on a craft basis, and interchangeable parts would have very high unit cost
Unit cost
The unit cost of a product is the cost per standard unit supplied, which may be a single sample or a container of a given number. When purchasing more than a single unit, the total cost will increase with the number of units, but it is common for the unit cost to decrease as quantity is increased...
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.
How indexing is achieved in manufacturing
Indexing capability is provided in two fundamental ways: with or without ITInformation technology
Information technology is the acquisition, processing, storage and dissemination of vocal, pictorial, textual and numerical information by a microelectronics-based combination of computing and telecommunications...
.
Non-IT-assisted physical guidance
Non-IT-assisted physical guidance was the first means of providing indexing capability, via purely mechanical means. It allowed the Industrial RevolutionIndustrial Revolution
The Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, transportation, and technology had a profound effect on the social, economic and cultural conditions of the times...
to progress into the Machine Age
Machine Age
The Machine Age is a term associated mostly with the early 20th century, sometimes also including the late 19th century. An approximate dating would be about 1880 to 1945. Considered to be at a peak in the time between the first and second world wars, it forms a late part of the Industrial Age...
. It is achieved by jigs
Jig (tool)
In metalworking and woodworking, a jig is a type of tool used to control the location and/or motion of another tool. A jig's primary purpose is to provide repeatability, accuracy, and interchangeability in the manufacturing of products. A jig is often confused with a fixture; a fixture holds the...
, fixtures
Fixture (tool)
A fixture is a work-holding or support device used in the manufacturing industry. What makes a fixture unique is that each one is built to fit a particular part or shape. The main purpose of a fixture is to locate and in some cases hold a workpiece during either a machining operation or some...
, 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, are drill jigs, the turrets on manual turret lathe
Turret lathe
The turret lathe is a form of metalworking lathe that is used for repetitive production of duplicate parts, which by the nature of their cutting process are usually interchangeable...
s, indexing head
Indexing head
An indexing head, also known as a dividing head or spiral head, is a specialized tool that allows a workpiece to be circularly indexed; that is, easily and precisely rotated to preset angles or circular divisions...
s for manual milling machine
Milling machine
A milling machine is a machine tool used to machine solid materials. Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines...
s, rotary table
Rotary table
A rotary table is a precision work positioning device used in metalworking. It enables the operator to drill or cut work at exact intervals around a fixed axis...
s, 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. 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
IT-assisted physical guidance (for example, via NCNumerical control
Numerical control refers to the automation of machine tools that are operated by abstractly programmed commands encoded on a storage medium, as opposed to controlled manually via handwheels or levers, or mechanically automated via cams alone...
, CNC, or robotics
Robotics
Robotics is the branch of technology that deals with the design, construction, operation, structural disposition, manufacture and application of robots...
) has been developed since the World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
era and uses electromechanical and electrohydraulic servomechanism
Servomechanism
thumb|right|200px|Industrial servomotorThe grey/green cylinder is the [[Brush |brush-type]] [[DC motor]]. The black section at the bottom contains the [[Epicyclic gearing|planetary]] [[Reduction drive|reduction gear]], and the black object on top of the motor is the optical [[rotary encoder]] for...
s 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.