Supporting and Locating Principles 111
Supporting and Locating Principles describes important concepts related to supporting and locating a workpiece on a modular fixture. In many cases, operators require modular fixtures that can more closely match the size and shape of a unique or complex part. Supporting the part is crucial in preventing workpiece deformation, while locating the part ensures it is positioned in the correct place for more efficient and repeatable operations.
An understanding of how to support and locate parts on a fixture is a key aspect of several manufacturing operations, including machining, welding, and assembly. When designed to properly support and locate, a fixture helps improve production rates and finished part quality. After taking this class, users will have an understanding of concepts, practices, and devices related to supporting and locating a workpiece on a fixture.
Number of Lessons 18
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- Workholding in Manufacturing
- Degrees of Freedom
- Locating Workpieces
- Supporting Workpieces
- Clamping Workpieces
- Workholding Basics Review
- Locator Selection
- Locator Placement
- Locator Tolerance
- External Versus Internal Locating
- Common Locating Approaches
- Other Locating Approaches
- Locating Issues
- Locating Review
- Support Selection
- Support Placement
- Common Support Approaches
- Final Review
- Describe workholding.
- Describe the 12 degrees of freedom.
- Describe workpiece location.
- Describe workpiece support.
- Describe workpiece clamping.
- Describe general considerations for selecting a locator.
- Describe general locator placement considerations.
- Describe locator tolerance.
- Distinguish between external locating and internal locating.
- Describe common locating approaches.
- Describe other locating approaches.
- Describe issues that can arise when locating a workpiece.
- Describe general considerations for selecting a support.
- Describe general support placement considerations.
- Describe common support approaches.
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.
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.
The rotational axis around the X axis. The A axis is one of three rotational axes.
Conforming closely to a given standard. Accurate surfaces closely match the required tolerance and surface finish for a part.
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.
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.
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.
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.
The rotational axis around the Y axis. The B axis is one of three rotational axes.
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.
A rectangular piece of metal used to reinforce a machining operation. Blocks provide a large locating and support area but must be precisely machined.
Shaped with a long body and tipped with a rounded cone. Bullet pins fit chamfered holes for internal location.
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.
A fixture component with a flat, circular head. Buttons fit in the holes on fixtures and provide both external locating and support.
The rotational axis around the Z axis. The C axis is one of three rotational axes.
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.
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.
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.
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.
Securely holding a workpiece against locators. Clamping a workpiece helps it resist the cutting forces that occur during machining.
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.
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.
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.
Shaped like a cone. Conical pins fit tapered holes for internal location.
The various stresses involved in a machining process. Cutting forces are one factor for determining locator placement.
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.
A type of fixture locating device with a polygon-shaped head. Diamond pins are used as internal locators for radial location.
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.
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.
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.
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.
A stationary locating component. Fixed locators provide stable and rigid setups.
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.
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.
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.
A force that resists motion between two components that are in contact with one another. Friction helps clamps secure workpieces.
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.
The process of restricting workpiece movement by placing locators against an internal surface. Internal locating is more efficient and accurate than external locating.
Extending indefinitely along a straight line. Linear movement includes up and down, left and right, and back and forth motion.
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.
A fixed locator that surrounds the outside surface of a workpiece. Locating nests are pockets machined directly into the surface of a fixture body.
A fixture component that positions the workpiece and restricts its movement. Locators must be used in combination with clamping in workholding.
Shaped through a manufacturing operation such as metal cutting. Machined surfaces are more even and smooth than unmachined surfaces.
The process of removing material to shape, size, or finish a part. Machining processes include metal cutting, grinding, and sawing.
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.
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.
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.
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.
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.
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.
Intersecting at a right, or 90° angle. Designers must locate at least two perpendicular surfaces on a workpiece in plane location.
A cylindrical device, sometimes with a shaped head, used on fixtures to restrict workpiece motion. Pins are the most commonly used fixture locating component.
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.
A flat, level surface. Planes are used for external location in fixture design.
An interior recess in the surface of a workpiece. Pockets can be circular, rectangular, or irregular.
A solid component that prevents the movement of another object. Positive stops on fixtures are the locators and supports.
The exertion of mechanical force on an object. Clamping pressure is necessary to restrict the upward motion of a workpiece.
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.
The speed at which a manufacturing operation produces parts. Production rates can be improved through the selection of proper workholding.
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.
A locator used to restrict rotational movement. Radial locators are used together with concentric locators.
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.
Moving or extending in a circular path around an axis. Rotational movement can occur in both clockwise and counterclockwise directions around a linear axis.
Raised, textured, and uneven. Rough surfaces are challenging to locate because they are uneven.
Shaped with a smooth, curved surface. Round pins reduce binding when used as internal locators.
Discarded. Scrapped parts are a waste of time, money, and resources.
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.
The position of tooling and fixturing for a machining operation. Fixture setup includes the placement of locators, supports, and clamps.
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.
A narrow channel in the surface of a workpiece. Slots can be straight or curved.
A description of the essential physical and technical properties of an object. Specifications for fixtures include measurements, tolerances, and fixture material, among other attributes.
The rate at which a cutting tool rotates in machining. Speed affects the amount of cutting forces on a located workpiece.
Shaped with a symmetrical domed surface. Spherical pins fit well into curved surfaces.
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.
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.
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.
A type of alloy steel that contains a large percentage of chromium. Stainless steels exhibit excellent corrosion resistance.
A fixture clamping device made from a series of interchangeable components. Strap clamps have slower setup speed but good clamping force.
Reinforcing a workpiece around its exterior or from underneath. Supporting a workpiece helps prevent workpiece deformation.
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.
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.
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.
An unwanted but acceptable deviation between an actual part dimension and its intended design. Tolerances are assessed during the inspection stage of manufacturing.
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.
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.
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.
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.
The erosion of material as a result of friction. Wear typically is caused by two or more objects rubbing or sliding against each other.
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.
A device used to secure, support, and locate a workpiece during a manufacturing operation. Common workholding devices include chucks, collets, and vises, among others.
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.
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.
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.
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.