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
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
Thickness gauges Medium resolution devices : Medium resolution devices Micrometer
Micrometer with assistance of
Extendable ball gauges
Microscope High resolution devices : High resolution devices Gauge blocks
Gauge block with assistance of
Optical flats Linear Measuring Instruments : Linear Measuring Instruments Vernier caliper
Slip gauge or gauge blocks
Comparators Vernier caliper : Vernier caliper Components of vernier calipers are
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 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
1. Vernier scale division =49\50 mm
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 : VERNIER DEPTH GAUGE Base
Fine adjustment mechanism
Vernier scale VERNIER HEIGHT GAUGE : VERNIER HEIGHT GAUGE The main parts of a vernier height gauge and their function are given.
4. fine setting device
5. vernier plate
6. locking screws
7. scriber MICRO METER : 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 : PARTS OF MICROMETER Frame
Anvil and spindle
Graduated sleeve or barrel
Ratchet or friction stop
Spindle clamp Interval measurements : Interval measurements Slip gauges
Optical flats and limit gauges
Comparators SLIP GAUGE : 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
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
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 : 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 : 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
If the work piece is concave or convex, fringe pattern will be as shown in Figure (b).
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 : Working Fringe Pattern : Fringe Pattern Air wedges
Flatness error of zero
Cylinder with flatness error of two fringes
Highly Irregular Air wedge : Air wedge Flatness error of zero (a)
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
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
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 : 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 : 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
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