Lecture 2 Flashcards
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What is A sine bar used to do?
A sine bar is used to measure angles based on the sine principle. Its upper surface forms the hypotenuse of a triangle formed by a steel bar terminating in a cylinder near each end. When one of the cylinders, called a roller, is resting on a flat surface, the bar can be set at any desired angle by simply raising the second cylinder. The required angle is obtained when the difference in height between the two rollers is equal to the sine of the angle multiplied by the distance between the centres of the rollers. Figure 1.12 illustrates the construction details of a sine bar.
What is A true square is used as a companion tool along with an angle gauge block set. It is available for both tool room and laboratory master sets. As the name itself suggests, it?
square piece made of hardened and wear-resistant steel. All faces of the true square are precisely at a 90° angle to adjacent gauging surfaces. It has a high degree of optical flatness and parallelism to be used with autocollimators. The main advantage of a true square is that it extends the range of the angle block set to 360°, be it in degree, minute, or second steps. Figure 1.11 illustrates the shape of a true square.
What are At the outset, it seems improbable that a set of 10 gauges is sufficient to build so many angles. However, angle blocks have a special feature that is impossible in slip gauges—the former can be subtracted as well as added. This fact is illustrated in Fig. 1.7. This illustration shows the way in which two gauge blocks can be used in combination to generate two different angles. If a 5° angle block is used along with a 30° angle block, as shown in Fig. 1.7(a), the resulting angle is 35°. If the 5° angle block is reversed and combined with the 30° angle block, as shown in Fig. 1.7(b), the resulting angle is 25°. Reversal of an angle block subtracts itself from the total angle generated by combining other angle blocks. This provides the scope for creating various combinations of angle gauges in order to generate angles that?
spread over a wide range by using a minimum number of gauges.
What is An autocollimator is an optical instrument that used to do?
An autocollimator is an optical instrument that is used to measure small angles with very high sensitivity. It has a wide variety of applications, including precision alignment, detection of angular movement, verification of angle standards, etc. The user has a wide choice of instruments from the conventional visual collimator to the digital and laser autocollimators.
What are A sine bar can also be used to measure unknown angles with a high degree of precision. The angle of the work part is first measured using an instrument like a bevel protractor. Then, the work part is clamped to the sine bar and set on top of a surface plate to that angle using slip gauges, as shown in Fig. 1.15 (clamping details?
not shown in the figure).
What are Most of the universal protractors in use?
of this type. An acute angle attachment is provided to facilitate measurement of acute angles on work parts. A clamp is provided to lock the reading, so that it can be read and recorded at a convenient position by the user.
What are Conical workpieces that need to be inspected?
placed between the centres. The sine centre is used for measuring angles up to 60°. The procedure for measuring angles is very similar to the one described in Section 1.4.2. A dial gauge clamped to a stand is set against the conical workpiece. The sine bar is set to an angle such that the dial gauge registers no deviation when moved from one end of the workpiece to the other. The angle is determined by applying the sine rule.
What are 24 vernier divisions correspond to 46 main-scale divisions. From Fig. 1.2, it is clear that one vernier division equals 1/12th of 23°. Let us assume that the zeroth division on both the main and the vernier scales?
lined up to coincide with each other. Now, as the dial rotates, a vernier division, starting from the fifth minute up to the 60th minute, progressively coincides with a main scale division until the zeroth division on the vernier scale moves over the main scale by 2°.
What are Let us assume a 100 mm-long sine bar and calculate the heights to set it at 30°, 45°, and 60°, as shown in Fig. 1.14. The heights?
respectively 53, 73.71, and 89.6 mm for angles 30°, 60°, and 90°.
What are If one traces the history of the development of angle-measuring devices, the bevel protractor preceded the universal bevel protractor. The earliest bevel protractor had a simple mechanism that facilitated the rotation of measuring blades and locked them in place. It had a scale graduated in degrees on which the measurements could be directly read. However, these instruments have largely been replaced by universal bevel protractors and the older types?
not being used in metrology applications now. Therefore, we shall directly go to a discussion on the universal bevel protractor.
What is By building slip gauges to height h and placing the sine bar on a surface plate with one roller on top of the slip gauges, the upper surface can be set to a desired angle with respect to the surface plate. The set-up is easier because the cylinders are integral parts of the sine bar and no separate clamping is required. No measurement is required between the cylinders since this?
known length. It is preferable to use the sine bar on a grade A surface plate. In addition, it is desirable to support both rollers on gauge blocks so that the minute irregularities of the surface plate may be eliminated.
What are Figure 1.9 shows a workpiece with a compound angle. Let us assume that the back angle (α) is 15°20’ and the side angle (β) is 5°. In order to set the workpiece to 15°20’, two angle gauge blocks of 15° and 20’?
selected and wrung together. This combination is placed on a surface plate, and the workpiece is positioned on top of the angle gauges. Now, the dial indicator reading is taken along a longitudinal direction. If the reading remains zero, it indicates a conformance of the angle α; in this case, the back angle is 15°20’. Then, a 5° angle block is selected and is positioned across the workpiece in the transverse direction, as shown in the figure.
What is From the calibration point of view, it is much easier to calibrate angle gauge blocks compared to slip gauges. This is due to the fact that an angle being measured?
portion of a full circle and is, therefore, self-proving. For instance, each of three exactly equal portions of 90° must equal 30°. Thus, the breakdown system can be used to create masters of angle measuring, and each combination can be proved by the same method. In addition, the accuracy of angle gauges is not as sensitive to temperature changes as that of slip gauges. For example, a gauge block manufactured at, say, 30 °C will retain the same angle when used at 40 °C, assuming that the readings are taken some time after the temperature has stabilized and the whole body of the gauge is exposed to the same temperature.
What are In all these three devices, the work part rests on them. They?
often used like a fixture to keep the work part at a particular orientation, so that the required angle is machined. The instruments have attachments to raise and lock the block to the required angle, and to also fasten work parts. The sine table is the most rugged device, which may be swung to any angle from 0° to 90° by pivoting about the hinged end.
What are Length standards such as foot and metre?
arbitrary inventions of man. This has necessitated the use of the wavelength of light as a reference standard of length because of the difficulty in accurately replicating the earlier standards. On the other hand, the standard for angle, which is derived with relation to a circle, is not man-made but exists in nature. One may call it degree or radian, but the fact remains that it has a direct relation to a circle, which is an envelope of a line moving about one of its ends. Whether one defines a circle as the circumference of a planet or path of an electron around the nucleus of an atom, its parts always bear a unique relationship.
What are The following?
some of the typical applications of visual autocollimators:
What are The newly manufactured or in-use angle gauges?
subjected to calibration to ensure accuracy. One of the popular calibration methods for angle gauges is the interferometry method, which is quite a simple and accurate way of calibrating angle gauges.
What is The precise measurement of angles is an important requirement in workshops and tool rooms. We need to measure angles of interchangeable parts, gears, jigs, fixtures, etc. Some of the typical measurements are tapers of bores, flank angle and included angle of a gear, angle made by a seating surface of a jig with respect to a reference surface, and taper angle of a jib. Sometimes, the primary objective of angle measurement is not to measure angles. This may sound rather strange, but this is the case in the assessment of alignment of machine parts. Measurement of straightness, parallelism, and flatness of machine parts requires highly sensitive instruments like autocollimators. The angle reading from such an instrument?
measure of the error of alignment.
What is A bevel protractor?
precision angle-measuring instrument. To ensure an accurate measurement, one should follow these guidelines:
What are TL40 and TL160 lasers?
popular in autocollimators. Table 1.3 gives a comparative picture of the capabilities of these two lasers.
What are You?
perhaps aware of the power of laser and impracticability of direct viewing of laser beam unlike the conventional source of light. Therefore, an alternative method has to be developed to capture the readings of the instrument. Figure 1.20 illustrates the construction details of a laser collimator.
What are Angle gauges, which?
made of high-grade wear-resistant steel, work on a principle similar to slip gauges. While slip gauges can be built to give linear dimensions, angle gauges can be built to give the required angle. The gauges come in a standard set of angle blocks that can be wrung together in a suitable combination to build an angle. C.E. Johansson, who developed slip gauges, is also credited with the invention of angle gauge blocks. However, the first set of a combination of angle gauges was devised by Dr G.A. Tomlinson of the National Physical Laboratory, UK, in the year 1939, which provided the highest number of angle combinations. His set of 10 blocks can be used to set any angle between 0° and 180° in increments of 5’.
What are The following?
some of the applications of a digital autocollimator:
