Supporting and Locating Principles 111

12 degrees of freedom

The possible directions of movement for an object. The 12 degrees of freedom include linear movement along three axes and rotational movement around those axes.

3-2-1 method

A method of external locating that involves placing three locators against the bottom surface of the workpiece, two against one side of the workpiece, and one against the side right next to the two locators. The 3-2-1 method restricts 9 of the 12 degrees of freedom.

A axis

The rotational axis around the X axis. The A axis is one of three rotational axes.

accurate

Conforming closely to a given standard. Accurate surfaces closely match the required tolerance and surface finish for a part.

adjustable locator

A locating component that can vary in length or position. Adjustable locators may be threaded in order to move to accommodate workpieces of different sizes.

assembled locators

A separate locating component that is attached or fastened to the fixture or other workholding device. Assembled locators provide more setup flexibility but are less rigid.

assembly

A manufacturing process in which two or more components are joined together to create a finished part. During assembly, a workholding device holds components in the proper location for accurate joining.

axes

An imaginary straight line that is used to measure the location of an object in three-dimensional space. Axes in the Cartesian coordinate system include the X, Y, and Z axes.

B axis

The rotational axis around the Y axis. The B axis is one of three rotational axes.

binding

The sticking or wedging of a workpiece on a locator. Binding requires additional manufacturing time to separate the workpiece and locator, sometimes causing damage to one or both.

blocks

A rectangular piece of metal used to reinforce a machining operation. Blocks provide a large locating and support area but must be precisely machined.

bullet

Shaped with a long body and tipped with a rounded cone. Bullet pins fit chamfered holes for internal location.

burrs

A rough edge remaining on material, such as metal, after it has been machined. Burrs may cause injury and interfere with the fitting of workpieces in fixtures.

buttons

A fixture component with a flat, circular head. Buttons fit in the holes on fixtures and provide both external locating and support.

C axis

The rotational axis around the Z axis. The C axis is one of three rotational axes.

calipers

A measuring instrument with a pair of jaws on one end and a long beam containing a marked scale of unit divisions. Calipers can measure the dimensions of both internal and external features.

Cartesian coordinate system

A positioning method that uses three linear axes perpendicular to each other to describe the location of an object in three-dimensional space. The three linear axes in the Cartesian coordinate system are the X axis, Y axis, and Z axis.

castings

A part formed by pouring or injecting heated material into a mold. Castings have rough surfaces that usually require initial machining, or roughing, before they can be properly finished.

chips

A small piece of material that is removed from a workpiece. Chips can get caught between fixture components and the workpiece, reducing finished part accuracy.

chucks

A workholding device that secures a workpiece as it rotates on a lathe or other machine. Chucks commonly have three or four adjustable jaws that can be moved to fit workpieces of a variety of sizes.

clamping

Securely holding a workpiece against locators. Clamping a workpiece helps it resist the cutting forces that occur during machining.

clamps

A workholding component that tightens to hold a workpiece in place when it is exposed to the forces of manufacturing. Clamps include strap clamps, toggle clamps, and screw clamps.

combination locating

A type of location in which some locators are set against external surfaces and others are set against internal surfaces of the workpiece. Combination locating is generally used for irregular parts that have one internal feature.

concentric location

A type of location in which the locator is set inside a centrally located hole or around a cylindrical workpiece. Concentric location restricts 9 degrees of freedom with a single locator.

conical

Shaped like a cone. Conical pins fit tapered holes for internal location.

cutting forces

The various stresses involved in a machining process. Cutting forces are one factor for determining locator placement.

datum

A point of reference for machine tools, programs, and fixtures from which measurements are taken or positions are located. A datum can be a hole, a line, or any three-dimensional shape.

diamond pins

A type of fixture locating device with a polygon-shaped head. Diamond pins are used as internal locators for radial location.

distortion

Warpage in a workpiece due to stresses caused by exposure to pressure and other manufacturing forces. Distortion can be prevented through proper use of support devices.

duplicate locator

An unnecessary additional locator that restricts the same degree of freedom as another locator or takes the place of a clamp. Duplicate locators make unloading and loading more difficult and can still allow the workpiece to shift.

external locating

The process of restricting workpiece movement by placing locators against outside workpiece surfaces. External locating is more commonly used for flat or cylindrical workpieces with no holes.

feeds

The rate at which a cutting tool or workpiece advances during a machining operation. Feed measures tool movement along a workpiece in turning, milling, and grinding and tool movement into a workpiece in drilling.

fixed locators

A stationary locating component. Fixed locators provide stable and rigid setups.

fixture body

A component that provides the base for the other elements of a fixture. Fixture bodies include faceplates for lathes and base plates, angle plates, and tombstones for milling and drilling.

fixtures

A customizable, modular workholding device created by configuring locators, supports, and clamps on a base plate or worktable. Fixtures are useful when holding irregularly shaped workpieces or when holding multiple workpieces for a single operation.

fool-proofing locators

A locator that prevents an operator from loading a workpiece incorrectly in a fixture. Fool-proofing locators reduce the possibility of cutting a workpiece incorrectly due to operator error.

friction

A force that resists motion between two components that are in contact with one another. Friction helps clamps secure workpieces.

integral locators

A locating component that is built into or permanently fixed to the fixture or other workholding device. Integral locators are always fixed and provide highly stable and rigid setups.

internal locating

The process of restricting workpiece movement by placing locators against an internal surface. Internal locating is more efficient and accurate than external locating.

linear

Extending indefinitely along a straight line. Linear movement includes up and down, left and right, and back and forth motion.

locating

Establishing a workpiece in a set position. Locating a workpiece correctly ensures it will be machined or otherwise manufactured to the correct specifications and tolerance.

locating nest

A fixed locator that surrounds the outside surface of a workpiece. Locating nests are pockets machined directly into the surface of a fixture body.

locators

A fixture component that positions the workpiece and restricts its movement. Locators must be used in combination with clamping in workholding.

machined

Shaped through a manufacturing operation such as metal cutting. Machined surfaces are more even and smooth than unmachined surfaces.

machining

The process of removing material to shape, size, or finish a part. Machining processes include metal cutting, grinding, and sawing.

metal cutting

A machining process that uses a cutting tool to remove metal from a workpiece in the form of chips. Metal cutting operations include milling, drilling, and turning.

micrometers

A U-shaped measuring instrument with a threaded spindle that slowly advances toward a small anvil. Micrometers are available in numerous types for measuring the dimensions of a range of feature types and sizes.

mill

A rotating multi-point cutting tool that is guided along a workpiece to create flat surfaces or slots. Mills are also a type of machine tool used to perform milling operations on a workpiece.

milling

A cutting operation in which a rotating multi-point tool is fed along a part's surface to remove material. Milling operations are usually performed on flat or rectangular workpieces but can be performed on cylindrical workpieces with the use of a V-locator.

modular

Consisting of interchangeable and discrete parts. Modular components, such as assembled locators and supports on a fixture, can be individually replaced, rather than requiring replacement of an entire component.

operators

A person responsible for running a machine properly, safely, and efficiently. Operators are often responsible for correctly securing the workpiece in a workholding device, among other duties.

perpendicular

Intersecting at a right, or 90° angle. Designers must locate at least two perpendicular surfaces on a workpiece in plane location.

pins

A cylindrical device, sometimes with a shaped head, used on fixtures to restrict workpiece motion. Pins are the most commonly used fixture locating component.

plane location

A method of external locating in which locators are set against several flat surfaces on the workpiece. Plane location is the most common form of external location.

planes

A flat, level surface. Planes are used for external location in fixture design.

pockets

An interior recess in the surface of a workpiece. Pockets can be circular, rectangular, or irregular.

positive stops

A solid component that prevents the movement of another object. Positive stops on fixtures are the locators and supports.

pressure

The exertion of mechanical force on an object. Clamping pressure is necessary to restrict the upward motion of a workpiece.

prints

A document containing all the instructions necessary to manufacture a part. A print includes a part drawing, dimensions, and notes that describe the order and type of manufacturing operations and important part specifications.

production rates

The speed at which a manufacturing operation produces parts. Production rates can be improved through the selection of proper workholding.

radial location

A type of location in which movement is restricted around a concentric locator by eliminating rotational movement around the Z axis. Radial location can be internal or combination locating.

radial locators

A locator used to restrict rotational movement. Radial locators are used together with concentric locators.

relieved

Machined to have an angled or narrower surface to create space or a gap between components. Relieved locators have additional space for chips to escape and reduce the amount of surface area in contact between the workpiece and locator.

rotational

Moving or extending in a circular path around an axis. Rotational movement can occur in both clockwise and counterclockwise directions around a linear axis.

rough

Raised, textured, and uneven. Rough surfaces are challenging to locate because they are uneven.

round

Shaped with a smooth, curved surface. Round pins reduce binding when used as internal locators.

scrapped

Discarded. Scrapped parts are a waste of time, money, and resources.

screw clamps

A type of clamp that creates clamping force through the turning of a threaded device that connects to and grips a workpiece. Screw clamps have longer setup times but provide secure workholding.

setup

The position of tooling and fixturing for a machining operation. Fixture setup includes the placement of locators, supports, and clamps.

sight locators

A slot or mark on a fixture body that assists with part positioning. Sight locators help position a workpiece but do not restrict its movement.

slots

A narrow channel in the surface of a workpiece. Slots can be straight or curved.

specifications

A description of the essential physical and technical properties of an object. Specifications for fixtures include measurements, tolerances, and fixture material, among other attributes.

speeds

The rate at which a cutting tool rotates in machining. Speed affects the amount of cutting forces on a located workpiece.

spherical

Shaped with a symmetrical domed surface. Spherical pins fit well into curved surfaces.

spherical pin

A locator pin with a smooth, symmetrical dome at its tip. Spherical pins allow smooth rotation and prevent binding or jamming when used as a concentric locator.

spring

A flexible device made of coiled material that yields under force and returns to its original shape once the force is removed. Springs are used in some adjustable locators to allow movement of locator parts.

spring locating pins

An adjustable locator with a bulb attached to a spring. Spring locating pins move out of place while the workpiece is located and then spring back into position to help hold the workpiece.

spring-stop buttons

An adjustable locator with a flat head attached to a spring. Spring-stop buttons automatically adjust their size when a workpiece is pressed against them.

stainless steel

A type of alloy steel that contains a large percentage of chromium. Stainless steels exhibit excellent corrosion resistance.

strap clamps

A fixture clamping device made from a series of interchangeable components. Strap clamps have slower setup speed but good clamping force.

supporting

Reinforcing a workpiece around its exterior or from underneath. Supporting a workpiece helps prevent workpiece deformation.

supports

A fixture component that locates the workpiece's underside during machining to prevent it from breaking or deforming. Supports include rest buttons, support pins, and centers.

surface finish

The degree of smoothness on a part's surface after it has been machined or otherwise shaped. Surface finish can be improved through final machining processes such as grinding.

toggle clamps

A type of clamp with a clamping arm that rotates around a locking pivot pin. Toggle clamps lock into place when an operator pulls a lever down that immobilizes the pivot pin.

tolerance

An unwanted but acceptable deviation between an actual part dimension and its intended design. Tolerances are assessed during the inspection stage of manufacturing.

tool steel

A grouping of steels designed to be used as fixture components, dies, punches, and other tools. Tool steels are designed for toughness, hardness, and wear resistance.

V-blocks

A locator that has an angled, notched interior in the shape of a "V". V-blocks, or V-locators, are used to position cylindrical or rounded workpieces for milling or drilling.

vises

A workholding device with two jaws, usually one fixed and one movable, that grip and hold a workpiece in place. Vises are often used to hold workpieces for milling, drilling, and grinding operations.

V-locators

A locator that has an angled, notched interior in the shape of a "v". V-locators, or V-blocks, are used to position cylindrical or rounded workpieces for milling or drilling.

wear

The erosion of material as a result of friction. Wear typically is caused by two or more objects rubbing or sliding against each other.

workholding

The process of securely supporting, locating, and clamping a workpiece for a manufacturing operation. Workholding helps to ensure that parts are created accurately and with good repeatability.

workholding devices

A device used to secure, support, and locate a workpiece during a manufacturing operation. Common workholding devices include chucks, collets, and vises, among others.

workpiece

An unfinished part that is subjected to one or more manufacturing operations in order to create a finished product. Workpieces can be shaped and finished through various manufacturing operations, such as metal cutting and assembly.

X axis

The linear axis representing side-to-side movement of an object relative to the origin. The X axis, along with the Y axis, is one of the two horizontal axes in the Cartesian coordinate system that together make up the X-Y plane.

Y axis

The linear axis representing back-and-forth movement of an object relative to the origin. The Y axis, along with the X axis, is one of the two horizontal axes in the Cartesian coordinate system that together make up the X-Y plane.

Z axis

The linear axis that represents the up-and-down motion of an object relative to the origin. The Z axis is the only vertical axis in the Cartesian coordinate system.