Machine Parts

                 Drill jigs                  Fixtures 1.A drill jig holds the workpiece   during drilling,tapping and reaming holes. 2. Jig is not fastened to machine. 3. Jig controls the path of cutting tool. 1.A fixture holds the workpiece during machining operations like milling,planning,shaping,turning etc operations. 2. Fixture is always fastened to machine tool. 3. Fixtures does not contain special arrangement for guiding the cutting tools.

                                                          The additional considerations applied to the lathe fixtures are given below: 1. Clamps and other holding devices should be designed in such a way that they will not be loosened by centrifugal force. 2. The workpiece should be gripped on its largest diameter,and whenever possible the gripping diameter should be larger than the diameter being machined. 3. The fixture should be well balanced.Irregular –shaped workpieces may have to be counter weighted to prevent vibration .It is not necessary to achieve perfect balance unless the workpiece is rotating at high speeds. 4. The fixtures should be as lightweight as possible since it is rotating. 5. projections and sharp corners should be avoided as the operator may not be able to see them while the tool is rotating. 6. Thin sections of the workpiece may require support to resist the pressure of the lathe tool

Advantages of magnetic and vacuum chucks are given bellow:  1. More economical. 2. Reduces the size of the machine table table needed. 3. A given number of parts can be mounted at one time or permits more parts per set up. 4. Smaller diameter cutters may be used since no clearance is required. 5. Able to hold thin and thin walled parts during turning and boring operations without distortion. 6. Ensures safety to the operator. 7. Provides heat free holding.  How face plate fixtures are located on the lathe face plate? A lathe faceplate fixture is fastened to a standard lathe faceplate and is usually built up from standard clamping and locating devices.The base of the fixture may be a flat plate bolted to the face plate,as shown in fig.(a),or it may be an angle plate,as shown in fig.(b).It is usually located on the faceplate by means of two dowel pins and secured by cap screws inserted through the faceplate into tapped holes in the fixture