Lathe Operations: Facing

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Facing Operations Facing is the process of removing metal from the end of a workpiece to produce a flat surface. Most often, the workpiece is cylindrical, but using a 4-jaw chuck you can face rectangular or odd-shaped work to form cubes and other non-cylindrical shapes.

When a lathe cutting tool removes metal it applies considerable tangential (i.e. lateral or sideways) force to the workpiece. To safely perform a facing operation the end of the workpiece must be positioned close to the jaws of the chuck. The workpiece should not extend more than 2-3 times its diameter from the chuck jaws unless a steady rest is used to support the free end. Cutting Speeds

If you read many books on machining you will find a lot of information about the correct cutting speed for the movement of the cutting tool in relation to the workpiece. You must consider the rotational speed of the workpiece and the movement of the tool relative to the workpiece. Basically, the softer the metal the faster the cutting. D…

Introduction to AC & DC Generators

In most of the earlier aircrafts, the aircraft electrical systems were planned on a basic DC power source. For DC power supply DC generators were used and for AC power requirements Invertors and alternators were used. With increased power requirements the basic DC power supplied by generators were found inefficient due to some related problems like commutation and high altitude operations. To overcome these difficulties all the modern aircrafts are now using AC as basic power source, generated by alternators.



In modern aircrafts, the latest aircraft electrical system has become 200V or 208V AC three phases 400 cycles/ second. The main AC is produced by one or two AC generators and DC power is supplied by transformer and rectifier unit (TRU). The battery is used as a stand by DC power and static Invertors are used as emergency AC power source.



AC Generator.         AC Generator is used to produce an alternating current.  In the AC generator slip rings with brushes used to collect the AC supply from the AC generator.  Its application based on set of winding.  If it has one set of winding it is called single-phase generator. It is used for low output. If a set of three winding is used then it is called three-phase generator, used to get large output. Their connections are given in star or delta fashion.



Types of AC Generator.    The Following are the types of AC generators:



 (a)          Rotating armature type.



 (b)          Rotating field type.



DC Generator.         Dc Generator is used to produce direct current. by replacing slip rings in AC Generator with split rings (commutator),alternating current is changed as direct current in the external circuit.

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