INTRODUCTION TO METROLOGY MODULE 1 MECH_INT CLASSES 5TH SEM MECHANICAL
BY Prof. Avinash
CONTENTS
Metrology basics Standards and comparators Limits, fits, tolerances and gauges Angular measurement
METROLOGY BASICS
Definition of metrology Scientific metrology, Industrial metrology, Legal metrology Need of inspection
Definition of metrology 
It is a science of measurement

It is divided upon the quantity under consideration
Categories of metrology 
Industrial metrology

Scientific metrology

Legal metrology
Need of inspection
To ensure that the part conforms to established standard To meet interchangeability of manufacture To maintain customer relations To find shortcomings in manufacture Helps to purchase good quality of raw materials Helps co-ordination of different departments To take decision on defective parts
Standards and comparators
Types of material standards Slip gauge and its accessories Need for Comparators Working principle of comparators Types of comparators
Types of Material Standards 
 1. 2.
3.
A material standard is an ultimate reference for unit quantities Types of material standards: Line standards End standards Wavelength standards
Angular measurements 
 1. 2.
3. 4. 5. 6.
Angle: opening between two intersecting lines Instruments used: Universal bevel protractor Sine bar Angle gauges Clinometer Angle dekkor Auto colliminator
Universal bevel protractor
Sine bar
Angle gauges
Clinometers
Screw measurements 
 1. 2. 3. 4. 5.
6.
ISO grade and fits of thread(SS) Errors in threads Major diameter Minor diameter Effective diameter Pitch Flank angles Profile at crest and root
Pitch Errors
Progressive error
Periodic error
Drunken error
Erratic or irregular errors
Measurement of major diameter
Measurement of Minor Diameter
Measurement of effective Dia.(2 wire method)
Thread gauge micrometer
Principle of floating carriage Dial micrometer
Contd.
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Gear measurement and testing
Analytical and functional inspection Rolling test Measurement of tooth thickness(constant chord method) Gear tooth vernier Errors in gears(Backlash, run-out, composite)
Analytical inspection 
1.
2. 3.
4. 5.
6. 7. 8. 9.
It consists of determining the following teeth elements in which manufacturing errors may be present Runout(Tester with dial indicator gives the error) Pitch(comparator and direct angular measurement) Profile(optical projection, involute mm, tooth disp. method) Lead (lead checking instrument) Backlash(locking and measuring)(tooth space-tooth thickness ) Tooth thickness(constant chord method) Concentricity Alignment Composite errors(rolling test)
Rolling test (Parkinson’s test)
Master gear rotated with test gear Test gear mounted on varying platform Dial indicator to give the errors Electronic recorder to give variation
Measurement of tooth thickness Constant chord method 1.Constant chord is the chord joining those points on opposite faces of the tooth which make contact with mating teeth when the centre line of the tooth lies on the line of gear centers. 2. The value of CC can be mathematically calculated and verified by the instrument 3. advantage: it can be applied for all no. of teeth of same module as the value of constant chord is same 
Gear tooth vernier 
1. 2. ď ą
It has two arms: For measuring tooth thickness For measuring addendum The measured value compared with calculated
Errors in gears
Backlash
Runout
Composite
Testing techniques 
Measurement of surface finish

Machine tool testing
Measurement of surface finish 1.
2.
3. 4. 5.
6. 7.
Factors affecting surface roughness Order of geometrical irregularities (Primary and secondary texture) Lay (with direction) Sampling length Evaluation of surface finish (CLA, Ra, RMS, Rz) Symbol for representing surface finish Various techniques of qualitative analysis
Factors affecting surface roughness
Vibrations Material of W/P Type of machining Rigidity of m/c system Sharpness and form of cutting tool Cutting conditions Type of coolant used
Order of geometrical irregularities 
1.
2.
3.
Primary texture Surface roughness of small WL are called primary texture Caused by direct action of cutting tool factors(speed, feed, depth of cut, friction) Lr/Hr<50 (microerrors)
Contd. ď&#x201A;¨
1.
2.
Secondary texture Surface irregularities of considerable WL of a periodic character are called secondary texture Lw/hw>50
Lay (with direction) ď&#x201A;¨
ď&#x201A;¨
It is the direction of predominant surface pattern produced by tool marks or scratches It is dependent on the method of production used
Evaluation of surface finish
Peak to valley height method
Average surface roughness method
Form factor or bearing curve method
The average roughness method CLA(centre line average) method 1. It is the average of the values of ordinates(heights) from the mean line, regardless of the sign of ordinates. 2. CLA value = (h1+h2+…hn)/n = (A1+A2+…An)/L Area values can be easily measured by planimeter
Contd. ď&#x201A;¨
1.
RMS value method: It is the square root of the arithmatic mean of the values of the squares of the ordinates of the surface measure from mean line.
Ten point height method ď&#x201A;¨
In this method , the average difference between the five highest peaks and five lowest valleys of the surface texture.
Conventional method for designing surface finish 1.
2. 3. 4.
5.
Roughness value in Ra (Îźm) Machining value in mm Sampling length in mm Machining or production method Direction of lay
Inspection techniques: ď&#x201A;¨
1. 2. 3. 4. 5. 6. 7.
8.
Inspection by comparison Visual inspection Touch inspection Scratch inspection Microscopic inspection Surface photographs Micro-interferometer Wallace surface dynamometer Reflected light intensity
Contd. Direct instrument: 1. If a finely pointed probe be moved over the surface of a W/P, the vertical movement of the stylus caused due to irregularities in the surface texture can be used to access the surface finish of the W/P. Methods: 1. Profilometer 2. Taylor hobson talysurf 3. Sigma microtest 4. Rubert indicator ď&#x201A;¨
Profilometer
Tomlinson surface meter
Taylor Hobson
M/c tool testing
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