Transcript
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Welcome to Session on metrology
E.Gowdhaman
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Session Four
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• Comparators and Definition
• Measuring Instruments & Comparators
• Mechanical Comparators
• Advantages and Disadvantages. protractor
Out Line
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Review of Angles • Angle is defined as the opening between two lines which meet
at a point.• The basic unit in angular measurement is the right angle. • For engineering purpose, the angular units are defined in
sexagesimal system* i-e Degree, Minutes, Seconds• Angular measurement is generally concerned with the
measurement of individual angles on gauges, tools, as well as small angular changes and deflections
• Only because of perfect/precise angular measurement that ships and aero plane can navigate confidently with out the help of sight of land.
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* Engineering Metrology by R.K.Jain page 517
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Fixed angle
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• In workshop, in most cases, the following Fixed Angle Measurement are used
• 30, 45, 60, 90, 120, 135 Deg.
• Try Square is one such Example for 90Deg measurement.
• 120Deg Square
• 135deg Square
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Squares• The solid square is usually used to
check squareness of surfaces or to square up parts on a surface plate prior to inspection
• There are many useful tools that can be used to precisely measure or check for squareness.
• The most common perhaps is the solid square/Tool makers Squares (see Figure).
• The wide portion is referred to as the beam and the slender upright portion is called the blade.
.
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Protractor• It is to measure the angle between
the two faces of a component• The plate protractor is capable of
measuring to within 1-degree. The plate protractor is especially useful for layout.
• Consist of steel flat bar with degree and movable blade
• Can be measured upto 30 min.
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Adjustable Bevel• Used to check, measure and
transfer angles and laying out work
• With Adjustable bevel, two bladed are set and locked in any position by locking screw
• Then angles are checked by another measuring devise
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Combination set
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Consist of 4 parts located in the groove of the blade
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Combination set• Protractor Bevel can be
adjusted only by direct application to lines or surfaces having the proper angular relation.
• It often happens that such adjustment is not feasible and, therefore, a registering device, in the form of a graduated arc, is applied to the bevel, making what is known as a protractor. This tool can be used to find the angular relation in degrees
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Combination set• Center Square: Center of a circle is found at the
intersection of any two diameters, an instrument for readily finding that point is a great convenience.
• This fig. shows a combination straightedge and square, called a center square, which accomplishes this result.
• As one edge of the rule bisects the angle of the square, it is evident that a line drawn by that edge passes through the center of any circular piece to which the square is applied.
• Locating centers in the ends of round bars or circular work of any kind is the principal use of this tool.
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Universal Bevel Protractor• Also called Vernier
Bevel Protractor• Used for measuring and
testing angles.• Accuracy of this
instrument is 5minutes• Fig shows typical
Vernier Bevel Protractor.
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Universal Bevel ProtractorParts: Consist of Base, Sliding Blade, Graduated
Disc(Main Disc), Vernier Scale
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Universal Bevel ProtractorFunction • The Protractor disc is
free to rotate at the pivot and can be clamped with the nut in base in assembly.
• Blade can slide both ways.
• VS fitted with disc to take reading during measurement.
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Universal Bevel Protractor
• The protractor ‘s disc is graduated in Degrees over an arc 180 Deg,
• It reads Zero to 90Deg both side of Zero line
• VSD has 12 Div both sides of Zero line.
• MSD is matched with 23 Div of VSD
• So 1 Div on Vernier Scale is 23Deg/12
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Reading Universal Bevel protractor
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• 1 Div on Vernier Scale is 23Deg/12
• Difference between the 2div on MSD& 1 Div on the VSD
• So
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Universal Bevel ProtractorCalculating Least count Universal Bevel protractor
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Reading Universal Bevel protractor• 1st of all, note the No. of whole Deg bet. Zero on VSD. Whole degree equal to
52Deg
• In VDS matching with 45Degs
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CASE 1
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Reading Universal Bevel protractorCASE 2
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Reading Universal Bevel protractorDo Your Self
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Reading Universal Bevel protractorDo Your Self
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Reading Universal Bevel protractorDo Your Self
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Reading Universal Bevel protractorDo Your Self
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Measuring Acute Angles Measuring Obtuse Angles
Different Methods/Purpose•The universal bevel protractor is capable of measuring obtuse angles as well as acute angles •When accompanied with the correct attachments. Look at Figure below to give you an idea as to the uses of the universal bevel protractor.
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Different Methods/Purpose Attachments
Using a protractor with a vernier height gage
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Reading Suggestions
• Engineering Metrology by R.K.Jain
page 517-520• All about machine tool by New age int.
(2nd Ed.) Page 112-115• A text book of Work shop Technology
Page 439-441• Web portal http://chestofbooks.com
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