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Types and Functions of Jigs and Fixtures - vk_afsal - 10-04-2017 Types and Functions of Jigs and Fixtures JIGS AND FIXTURES Jigs and fixtures are production-workholding devices used to manufacture duplicate parts accurately. The correct relationship and alignment between the cutter, or other tool, and the workpiece must be maintained. To do this, a jig or fixture is designed and built to hold, support, and locate every part to ensure that each is drilled or machined within the specified limits. Jigs and fixtures are so closely related that the terms are sometimes confused or used interchangeably. The difference is in the way the tool is guided to the workpiece. A jig is a special device that holds, supports, or is placed on a part to be machined. It is a production tool made so that it not only locates and holds the workpiece but also guides the cutting tool as the operation is performed. Jigs are usually fitted with hardened steel bushings for guiding drills or other cutting tools (Figure 2 1A). As a rule, small jigs are not fastened to the drill press table. If, however, holes above .25 inch in diameter are to be drilled, it is usually necessary to fasten the jig to the table securely. A fixture is a production tool that locates, holds, and supports the work securely so the required machining operations can be performed. Set blocks and feeler or thickness gauges are used with fixtures to reference the cutter to the workpiece (Figure 2 1B). A fixture should be securely fastened to the table of the machine upon which the work is done. Though largely used on milling machines, fixtures are also designed to hold work for various operations on most of the standard machine tools. Fixtures vary in design from relatively simple tools to expensive, complicated devices. Fixtures also help to simplify metalworking operations performed on special equipment. CLASSES OF JIGS Jigs may be divided into two general classes: boring jigs and drill jigs. Boring jigs are used to bore holes that either are too large to drill or must be made an odd size (Figure 2 2). Drill jigs are used to drill, 8 UNIT 2 Types and Functions of Jigs and Fixtures 75028_Hoffman_CH02 7/7/03 6:16 AM Page 8 ream, tap, chamfer, counterbore, countersink, reverse spotface, or reverse countersink (Figure 2 3). The basic jig is almost the same for either machining operation. The only difference is in the size of the bushings used. TYPES OF JIGS Drill jigs may be divided into two general types, open and closed. Open jigs are for simple operations where work is done on only one side of the part. Closed, or box, jigs are used for parts that must be machined on more than one side. The names used to identify these jigs refer to how the tool is built. Template jigs are normally used for accuracy rather than speed. This type of jig fits over, on, or into the work and is not usually clamped (Figure 2 4). Templates are the least expensive and simplest type of jig to use. They may or may not have bushings. When bushings are not used, the whole jig plate is normally hardened. TYPES OF FIXTURES The names used to describe the various types of fixtures are determined mainly by how the tool is built. Jigs and fixtures are made basically the same way as far as locators and positioners are concerned. The main construction difference is mass. Because of the increased tool forces, fixtures are built stronger and heavier than a jig would be for the same part. Plate fixtures are the simplest form of fixture (Figure 2 17). The basic fixture is made from a flat plate that has a variety of clamps and locators to hold and locate the part. The simplicity of this fixture makes it useful for most machining operations. Its adaptability makes it popular. The angle-plate fixture is a variation of the plate fixture (Figure 2 18). With this tool, the part is normally machined at a right angle to its locator. While UNIT 2 Types and Functions of Jigs and Fixtures 13 Figure 2 11 Channel jig. Figure 2 10 Box or tumble jig. 75028_Hoffman_CH02 7/7/03 6:16 AM Page 13 most angle-plate fixtures are made at 90 degrees, there are times when other angles are needed. In these cases, a modified angle-plate fixture can be used (Figure 2 19). Vise-jaw fixtures are used for machining small parts (Figure 2 20). With this type of tool, the standard vise jaws are replaced with jaws that are formed to fit the part. Vise-jaw fixtures are the least expen- Types and Functions of Jigs and Fixtures - pavan - 10-04-2017 to get information about the topic "jigs and fixtures" full report ppt and related topic refer the page link bellow http://seminarsprojects.net/Thread-types-and-functions-of-jigs-and-fixtures http://seminarsprojects.net/Thread-elements-of-jigs-and-fixtures?pid=76904&mode=threaded |