ME8501- Metrology and Measurments - Unit-4 Two marks

Subject Name: Metrology and Measurments

Subject Code: ME8501

B.E. Mechanical Engineering - semester 05

Anna University Regulation 2017 Mechanical 5th sem ME8501(Metrology and Measurments) 2 marks for 4th unit is provided below. ME8501 all units 2 marks, Metrology and Measurments all units notes , syllabus are listed down for students to utilize it for scoring maximum marks with our study materials.

1.Name the various types of pitch errors found in screw.

Answer

(i)Progressive error (ii)Drunken error (iii)Periodic error (iv)Irregular errors.

2.Name the various methods of measuring the minor diameter of the thread.

Answer

(i) Using taper parallels. (ii)Using rollers and slip gauges.

3.Name the various methods used for measuring major diameter.

Answer

(i) Ordinary micrometer (ii)Bench micrometer.

4.Define the effective diameter of thread.

Answer

Effective diameter is the average of minor and major diameter of thread.

5.Name the various methods for measuring effective diameter.

Answer

(i) One wire method (ii) Two wire method (iii)Three wire method.

6.Name the various methods for measuring pitch diameter.

Answer

(i) Pitch measuring machine (ii) Tool makers microscope (iii)Screw pitch gauge.

7.Define periodic error.

Answer

The periodic error repeats itself at equal intervals along the thread.

8.What are the commonly used forms of gear teeth?

Answer

1.Involute 2.Cycloidal

9.What are the types of gears?

Answer

1. Spur 2. Helical 3. Bevel 4. Worth and Worm wheel 5. Rack and pinion.

10.Define Lead.

Answer

It is defined as the distance at which a thread advances for one rotation. Lead = No.of starts x Pitch

11.Define lead angle.

Answer

It is the angle between the tangent to the helix and plane perpendicular to the axis of cylinder.

12.What are the various methods used for measuring the gear tooth thickness?

Answer

(i) Gear tooth vernier (ii) Constant chord method (iii)Base tangent method (iv) Measurement over pins.

13.Why is monochromatic light used in interferometry instead of white light?

Answer

Monochromatic light is used to suit radiations other than light. A most unusual feature of the interferometer is its high tolerance to large misalignment of its optical elements.

14.Define Module.

Answer

Module = Pitch circle diameter / Number of teeth

15.The outside diameter of a gear is 110mm and the number of teeth is 20. What is the module of gear?

Answer

Module = Pitch circle diameter / Number of teeth = 110 / 20

16.Name four gear errors.

Answer

(i) Pitch error (ii) Composite error (iii)Alignment error (iv) Thickness error.

17.Name the methods used for checking the pitch of the gear.

Answer

(i) Step by step method. (ii)Direct angular measurement.

18.What are the direct angular measurements methods?

Answer

1.Profile checking: a.Optical projection method. b.Involute measuring method. 2.Thickness measurment: a.Chordarl thickness method. b.Constance chord method.

19.Define constant chord.

Answer

Constant chord is the chord joining points or opposite faces of the tooth.

20.Give the formula for measuring radius of circle.

Answer

R = (l-d)²/8d where, R = Radius of the job l = Distance between the balls d = Diameter of pins.

21.What are the two methods used in measuring radius of concave surface?

Answer

a) Edges are well defined b) Edges are rounded up.

22.What are the factors affecting surface roughness?

Answer

a) Vibrations b) Material of the work piece c) Tool d) Machining type.

23.Define the term cut-off length with respect to surface roughness measurment.

Answer

The maximum wavelength considered for the measurement of surface roughness is known as cut-off length.

24.Define lays. Mention any four of its type.

Answer

It is the directio of the 'predominate surface pattern'. Types: (i)Horizontal lay (ii)Vertical lay (iii)Radial lay (iv)Circular lay.

25.What are the methods used for evaluating the surface finish?

Answer

a) Peak to valley height method. b) The average roughness method. c) Form factor method.

26.Define degree of fullness and degree of emptiness in form factor.

Answer

Degree of fullness is the ratio of area of metal considered to the area of enveloping the rectangle. Degree of fullness (K) = area of metal / Area of enveloping rectangle. Degree of emptiness is the ratio between the difference of the area of metal considered to the area of enveloping the rectangle and area of enveloping the rectangle. Degree of emptiness = 1 — K.

27.What are the methods used for measuring surface roughness?

Answer

a) Inspection by comparison b) Direct instrument measurements.

28.What are the stylus probe instruments?

Answer

a) Profilometer b) Taylor Hobson Talysurf c) Tomlinson surface meter.

29.Define straightness of a line in two planes.

Answer

A line is said to be straight over a given length of the variation of the distance of its points from two planes perpendicular to each other and parallel to the direction of a line remaining within the specified tolerance limits.

30.Define straight edge.

Answer

A straight edge is a measuring tool which consists of a length of a steel of narrow and deep section in order to provide a Considerable resistance to bending in the plane of measurement without excessive weight.

31.Compare straightness test by using spirit level and auto collimator.

Answer

Straightness test can be carried out by using a spirit level or auto collimator. The spirit level can be used only for the measurement of straightness of horizontal surface while auto collimator method can be used on the surfaces in plane. In the spirit level, the block is moved along the line on the surface to be tested in steps equal to the pitch distance between center lines of the feet and the angular variations of the direction of block are measured by the sensitive level on it. In auto collimator, the instrument is placed at a distance 0.5m to 0.75m from the surface to be tested.

32.Define roundness and name the four measurement of roundness.

Answer

It is a surface of the revolution where all surfaces are intersected by any plane perpendicular to a common axis in case of cylinder and cone. 1. Heart square circle. 2. Minimum radial separation circle. 3. Maximum inscribed circle. 4. Minimum circumscribed circle.

33.Name the devices used for the measurement of roundness.

Answer

1. Diametral 2. Circumferential confining gauge 3. Rotating on center 4. V-Block 5. Three point probe 6. Accurate spindle.

34.Define Cancentricity.

Answer

It is defined as the matching of components such as hollow shafts and spindles in a same line of operation i.e. in a single center.

35.What is gear runout?

Answer

It means eccentricity in the pitch circle. It will produce periodic vibration during each revolution of the gear. It will give the tooth failure in gears. It is also defined as the total range of a fixed indicator with the contact points applied to a surface rotated without axial movement about a fixed axis.

36.How the accuracy of a straight edge in specified and how it can be checked?

Answer

Specify the straight edge if the colour of light is red, a gap of 0.0012 to 0.0017 mm while for blue light it is 0.0075 mm.

37.What is secondary texture of a surface?

Answer

The surface irregularities of considerable wavelength of a periodic character are called secondary texture or waviness.

38.Define the term 'cut-off length' with respect to surface roughness measurement.

Answer

The maximum wavelength considered fbr the measurement of surface roughness is known as cut- off length.

39.Name the various stylus probe instruments used for surface finish measurement.

Answer

1. Tomlinson surface meter 2. Profilometer 3. Taysurf-surface roughness meter.

40.Mention the purpose of Goniometric heads in Tool maker's microscope.

Answer

Goniometric head in Tool maker's microscope is used to measure circular divisions / dimensions. For example, the flank angle of the gears may be measured using Tool Makers Microscope with a goniometric head.

41.List the reasons for the occurrence of progressive pitch errors in screw threads.

Answer

1. In correct linear and angular velocity ratio. 2. In correct gear train and lead screw. 3. Saddle fault. 4. Variation in length due to hardening.

42.Name the two corrections to be applied for the measurement of effective diameter.

Answer

(i) Rake corrections (ii)Compression correction

43.What is meant by "Best size wire" in screw thread measurement?

Answer

Best size of wire is a wire of such diameter that it makes contact with flanks of the thread on the pitch line.

44.How Taylor's principle is applied to screw thread gauge?

Answer

Maximum metal condition: It refers the condition of hole or shaft when the maximum material is left on i.e. high limit of shaft and low limit of hole. Minimum metal condition: It refers the condition of hole or shaft when the minimum material is left on such as low limit of shaft and high limit of hole. Statements: 1. The GO gauge must be made to check the maximum metal condition. 2. The NOGO gauge must be made to check the minimum metal condition.

45.Explain drunken error in screw threads.

Answer

It is one having erratic pitch in which the advance of helix is irregular in one complete revolution of thread.

46.What is the effect of flank angle error?

Answer

Errors in the flank cause a virtual increase in the effective diameter of a bolt and decrease in that of nut.

47.What are the applications of toolmaker's microscope?

Answer

(i)Linear measurement (ii)Measurement of pitch of the screw (iii)Measurement of thread angle.

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