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Unit 2Linear and Angular Measurement : 

Unit 2Linear and Angular Measurement

Syllabus : 

Syllabus Definition of metrology Linear measuring instruments: Vernier, micrometer and interval measurement- Slip gauges and classification. Interferometer, optical flats and limit gauges Comparators: Mechanical, pneumatic and electrical types, applications. Angular measurements: -Sine bar, optical bevel protractor ,Taper measurements

Definition : 

Definition Metrology is the name given to the science of pure measurement. Engineering Metrology is restricted to measurements of length & angle

Linear and Angular Measurement : 

Linear and Angular Measurement The Linear Measurement includes measurements of length, diameters, heights and thickness The Angular measurement includes the measurement of angles or tapers

Measurements : 

Measurements Measurement systems are mainly used in industries for quality control. Often widely using measurements are Linear Measurement Angular measurement

Dimensions : 

Dimensions A very common measurement is that of dimensions, i.e., length, width, height of an object Dimensions of the measuring instruments are classified as follows Low resolution devices (up to 0.25mm) Medium resolution devices (up to 0.0025mm) High resolution devices (less than microns)

Low resolution devices : 

Low resolution devices Steel rule Steel rule with assistance of Calipers Dividers & Surface gauges Thickness gauges

Medium resolution devices : 

Medium resolution devices Micrometer Micrometer with assistance of Telescoping Extendable ball gauges Vernier calipers Dial indicators Microscope

High resolution devices : 

High resolution devices Gauge blocks Gauge block with assistance of Mechanical comparator Electronic comparator Pneumatic comparator Optical flats

Linear Measuring Instruments : 

Linear Measuring Instruments Vernier caliper Micrometer Slip gauge or gauge blocks Optical flats Interferometer Comparators

Vernier caliper : 

Vernier caliper Components of vernier calipers are Main scale Vernier scale Fixed jaw Movable jaw Types of vernier calipers Type A vernier caliper Type B vernier caliper Type C vernier caliper

Type A Vernier Caliper : 

Type A Vernier Caliper

Type B Vernier Caliper : 

Type B Vernier Caliper

Type C Vernier Caliper : 

Type C Vernier Caliper


VERNIER CALIPER Vernier calipers are available in size of 150 mm, 225 mm, 900 mm and 1200 mm. The selection of the size depends on the measurements to be taken. Vernier calipers are precision instruments, and extreme care should be taken while handing them.

Vernier caliper : 

Vernier caliper VERIER CALIPER WITH 0.02MM LEAST COUNT IS GENERLY USED IM WORK SHOP. In this Vernier caliper main scale division (49mm) are divided in to 50 equal part in the Vernier scale. i.e. 1 main scale division =1 mm (MSD) 1. Vernier scale division =49\50 mm (VSD) Least count is 1mm – 49\50 =1\50 mm THE DIFFERENCE BETWEEN 1.MSD and 1. VSD=0.02MM

Example : 

Example Main scale reading =35mm The vernier division coinciding with the main scale is the 20th division. Value=20 multiplied by 0.02=0.40mm. Total reading is 35mm+0.40= 35.40mm 35.40 mm

Vernier Depth Gauge : 

Vernier Depth Gauge A vernier depth is very commonly used precision instrument for measuring depth of holes recesses, slot and step. Its construction and method of reading are similar to those of a vernier caliper.


VERNIER DEPTH GAUGE Base Graduated beam Clamping screw Fine adjustment mechanism Vernier scale


VERNIER HEIGHT GAUGE The main parts of a vernier height gauge and their function are given. 1.base 2. beam 3.vernier slide 4. fine setting device 5. vernier plate 6. locking screws 7. scriber


MICRO METER A micro meter is a precision instrument used to measure a job, generally within an accuracy of 0.01mm.Micrometer used to take the outside measurements are know as outside micrometer.


PARTS OF MICROMETER Frame Anvil and spindle Screwed spindle Graduated sleeve or barrel Ratchet or friction stop Spindle clamp

Interval measurements : 

Interval measurements Slip gauges Interferometer Optical flats and limit gauges Comparators


SLIP GAUGE Slip gauges are rectangular blocks of steel having a cross-section of about 30 by 10 mm Normal set

Slide 25: 

Special Set

Classification : 

Classification AA slip gauges A slip gauges and B slip gauges

Slide 27: 

AA slip gauges Master slip gauges Accurate to plus or minus two microns per meter A slip gauges Reference purpose Type A is guaranteed accurate up to plus or minus four microns per meter B slip gauges Working slip gauges Type 'B' for plus or minus eight microns per meter

Classes : 

Classes Grade 2 Grade 1 Grade 0 Grade 00 Calibration grade

Grade 2 : 

Grade 2 This is the workshop grade Typical uses include setting up machine tools, positioning milling cutters and checking mechanical width.

Grade 1 : 

Grade 1 Used for more precise work, -tool room. Typical uses include setting up Sine bars and sine tables Checking gap gauges and Setting dial test indicators to zero

Grade 0 : 

Grade 0 This is more commonly known as the Inspection grade Inspection Department only who have access to this grade of slips

Grade 00 : 

Grade 00 This grade would be kept in the Standard Room and would be kept for work of the highest precision only. Determination of any errors present in the workshop or Grade 2 slips.

Calibration grade : 

Calibration grade Calibration grade are used for calibration of slip gauges, other measuring instruments

Interferometer : 


Principle : 

Principle Interferometers are optical instruments used for measuring flatness Determining minute differences in length by direct reference to the wavelength of light.

Principle of interferometer : 

Principle of interferometer

Fringes : 


Fringes : 

Fringes a b c

Fringes : 

Fringes A Here the error is indicated by the amount by which the fringes are out of parallelism with those on the base plate B If the work piece is concave or convex, fringe pattern will be as shown in Figure (b). C The surface is flat with slight rounding off at the corner

Optical flats : 

Optical flats Optical flats can be used to measure the flatness An optical reference flat of known quality A monochromatic light box Solvent and cleaning material

Typical setup of optical flat : 

Typical setup of optical flat

Working : 


Fringe Pattern : 

Fringe Pattern Air wedges Flatness error of zero Cylinder with flatness error of two fringes Contact method Convex Cylinder Concave Cylinder Convex Sphere Concave Sphere Convex Spheroid Concave Spheroid Saddle Highly Irregular

Air wedge : 

Air wedge Flatness error of zero (a) (a) (b) Cylinder with flatness error of two fringes (b)

Contact method : 

Contact method Convex Cylinder Concave Cylinder

Slide 47: 

Saddle Highly Irregular

Application : 

Application Front and rear surface mirrors gauge blocks Bearings Seals and Anvils

Limit gauges : 

49 Limit gauges

Gauges : 

50 Gauges Basic dimension: exact size of part from which all limiting variations made Limits: maximum and minimum dimensions Tolerance: permissible variation of part unilateral: one direction only Bilateral: both plus and minus (two directions) Allowance: intentional difference in dimensions of mating parts

Fixed Gauges : 

51 Fixed Gauges Used for inspection purposes Provide quick means of checking specific dimension Easy to use and accurately finished to required tolerance Generally finished to ten times the tolerance designed to control

Cylindrical Plug Gauges : 

52 Cylindrical Plug Gauges Dimensions usuallystamped on handleat each end. Go "go" end longer than"no-go" for easyidentification Many made with carbidetips to increase gauge life

Cylindrical Plug Gauges : 

53 Cylindrical Plug Gauges

Cylindrical Plug gauge : 

54 Cylindrical Plug gauge

Plain Ring Gauges : 

55 Plain Ring Gauges Used to check outside diameter of pieces Ground and lapped internally to desired size Size stamped on side of gauge Outside diameter knurled and "no-go" end identified by annular groove on knurled surface Precautions and procedures similar to those outlined for a plug gauge

Plain Ring gauges : 

56 Plain Ring gauges

Taper Plug Gauges : 

57 Taper Plug Gauges Used to check size of hole and taper accuracy Made with standard or special tapers Some have "go" and "no-go" rings scribed gauge fits into hole between two rings means within required tolerance

Taper Plug and Ring Gauges : 

58 Taper Plug and Ring Gauges

Thread Plug Gauges : 

59 Thread Plug Gauges Used for checking internal threads of the "go" and "no-go" variety Based on same principle as cylindrical plug gauges "go" end (longer end) Should be turned in flush to bottom of hole "no-go" end Should just start into hole and become snug before third thread enters

Thread Plug Gauges : 

60 Thread Plug Gauges

Thread Ring Gauges : 

61 Thread Ring Gauges

Snap Gauges : 

62 Snap Gauges One of most common types of comparative measuring instruments Faster to use than micrometers Limited in their application Used to check diameters within certain limits by comparing part size to preset dimension of snap gauge

Snap Gauges : 

63 Snap Gauges Have C-shaped frame with adjustable gauging anvils or rolls set to "go" and "no-go" limits of the part Several styles


FEELER GAUGE A feeler gauge (also known as a thickness gauge) is an accurately manufactured strip of metal that is used to determine the gap or clearance between two components.


FEELER GAUGE A feeler gauge can be used to check the following: Piston ring gap Piston ring side clearance Connecting rod side clearance

Radius Gauge : 

Radius Gauge A radius gauge is a tool used to measure the radius of an object. 66

Thread Pitch Gauge : 

Thread Pitch Gauge It used to quickly determine the pitch of various threads by matching the teeth on the leaves with teeth on the work. 67

Comparators : 

Comparators Mechanical comparators Electrical comparators Optical comparators Pneumatic comparators

Mechanical comparators : 

Mechanical comparators

Slide 70: 

It is a precision instrument employed to compare the dimension of a given component with a working standard It does not measure the actual dimension but indicates how much it differs from the basic dimension

Electrical comparators : 

Electrical comparators

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