机电专业英语 教学课件 作者 杨寿智 刘水平 机电专业英语.Lesson 4.pptVIP

Lesson 4 Dial Indicating Instruments Text Machinists and toolmakers frequently use dial indicators. Dial indicators make it possible to quickly check correct alignment of one machine component with another and to correctly position workpieces in machine tools prior to machining. Dial indicating gages provide parts inspectors with a rapid and accurate way to check large quantities of nearly identical parts. Dial Indicators A dial indicator, Fig. 4.1, shows visually the amount of error, in size or alignment, for a part being measured or positioned as in Fig. 4.2. Metric dial indicators are calibrated in hundredths of a millimeter（0.01mm）, or in two thousandths of a millimeter (0.002 mm) units. Most inch dial indicators are calibrated in thousandths of an inch (0.001”), and ten-thousandths of an inch (0.0001”),but instruments with calibrations as fine as fifty-millionths of an inch (0.000050”) are available. There are two common types of dial indicators. The balanced type has figures in both directions from the zero , as in Fig. 4.3. The continuous reading type is numbered continuously, as in Fig. 4.9.The balanced type is the more widely used. Generally, smaller dial indicators are made with a smaller range of travel than larger dial indicators. Travel is frequently limited to one rotation of the dial pointer. Extended travel dial indicators are equipped with a second pointer which counts the number of revolutions of the main dial pointer, Fig.4.1. The dial reading may be set at zero at time simply by rotating the entire dial face. Dial Test Indicator Sets Dial test indicators sets are made for use in a wide variety of setup and inspection work. The set shown in Fig. 4.3 has a steel base with T-slots, and a column clamped to the base for holding the dial indicator. The dial indicator is first set to the proper gauging height. The gauging height is the basic dimension of the part to be gauged or tested. The gauging height may be established with gage blocks, with a plan