Lathe Operations: Us Army Correspondence Course Program (Subcourse No. Od1645) Edition 8

 
9781466419841: Lathe Operations: Us Army Correspondence Course Program (Subcourse No. Od1645) Edition 8
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1. Introduction- Lathes were developed as early as the 15th century and were known as "bow" lathes. The operator rotated the workpiece by drawing a bow back and forth, either by hand or with the use of a foot treadle. Next came Bessons lathe in 1568, which was driven by a cord passing over a pulley above the machine. This in turn drove two other pulleys on the same shaft which rotated the workpiece and a crude, wooden lead screw, which in turn allowed the operator to remove metal from the piece being machined. The screw cutting lathe originates in the 17th century. Development and advancements have continued and today we have sophisticated computerized controlled lathes. Lathes have allowed man to reshape, machine and manufacture many precision cylindrical components made of various types of metal, wood, plastics, and other materials. Without the lathe, man would still be trying to produce cylindrical components in some crude fashion or another. However, because of advanced technology, the lathe has allowed man to become an important asset in developing and machining many precision components needed to operate and function in many areas of our industrial complex. 2. Lathes Types and Uses.- a. General. The lathe is a machine tool used principally for shaping articles of metal, wood, or other material. All lathes, except the vertical turret type, have one thing in common for all usual machining operations; the workpiece is held and rotated around a horizontal axis while being formed to size and shape by a cutting tool. The cutter bit is held either by hand or by a mechanical holder, then applied to the workpiece. Principal capabilities of the lathe are forming straight, tapered, or irregularly outlined cylinders, facing or radial turning cylindrical sections, cutting screw threads, and boring or enlarging internal diameters. The typical lathe provides a variety of rotating speeds and suitable manual and automatic controls for moving the cutting tool. b. Types of Lathes. Lathes can be conveniently classified as engine lathes, turret lathes, and special purpose lathes. All engine lathes and most turret and special purpose lathes have horizontal spindles and, for that reason, are sometimes referred to as horizontal lathes. The smaller lathes in all classes may be classified as bench lathes or floor or pedestal lathes, the reference in this case being to the means of support. c. Engine Lathes. (1) General. The engine lathe is intended for general purpose lathe work and is the usual lathe found in the machine shop. The engine lathe may be bench or floor mounted; it may be referred to as a toolroom-type lathe, or a sliding-gap or extension-type lathe. The engine lathe consists mainly of a headstock, a tailstock, a carriage, and a bed upon which the tailstock and carriage move. Most engine lathes are back-geared and high torque, which is required for machining large diameter workpieces and taking heavy cuts. The usual engine lathe has longitudinal power and crossfeeds for moving the carriage. It has a lead screw with gears to provide various controlled feeds for cutting threads. Engine lathes are made in various sizes; the size is determined by the manufacturer. Generally, the size is determined by the following measurements: either (a) the diameter of the workpiece will swing over the bed, or (b) it will swing over the cross-slide, and (c) the length of the bed, or (d) the maximum distance between centers. For example, using method (a) and (c), a 14 inch x 6-foot lathe has a bed that is 6 feet long and will swing work (over the bed) up to 14 inches in diameter. The maximum distance between centers indicates the dimension, in inches, of the longest length of material that can be placed in the lathe.

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