METROLOGY.for engineering students 5th sem

SINCE MODERN PRODUCTION PROCESSES IS CONCERNED WITH
INTERCHANGEABLE PRODUCTS, PRECISE DIMENSIONAL
CONTROL IS REQUIRED IN INDUSTRY. PRECISION
MEASUREMENT INSTRUMENTS USE DIFFERENT TECHNIQUES
AND PHENOMENA TO MEASURE DISTANCE WITH ACCURACY .
INTRODUCTION

LINEAR MEASUREMENT
CLASSIFICATION OF LINEAR MEASURING INSTRUMENTS:
CLASSIFICATION BASED ON THE ACCURACY THAT CAN BE
OBTAINED FROM
1. NON PRECISION INSTRUMENTS
2. PRECISION INSTRUMENTS

NON PRECISION INSTRUMENT
 STEEL RULE
 CALIPER
TELESCOPIC GAUGE
DEPTH GAUGE

IT WORKS ON THE BASIC MEASURING TECHNIQUE OF
COMPARING AN UNKNOWN LENGTH TO THE ONE PREVIOUSLY
CALIBRATED. IT CONSIST OF A STRIP OF HARDENED STEEL
HAVING LINE GRADUATIONS ENGRAVED AT INTERVAL OF
FRACTION OF A STANDARD UNIT OF LENGTH. DEPENDING ON
THE INTERVAL AT WHICH THE GRADUATIONS ARE MADE, THE
SCALES CAN BE MANUFACTURED IN DIFFERENT SIZES AND
STYLES.

CALIPER
OUTSIDE CALIPERS MEASURE THICKNESSES AND OUTSIDE
DIAMETERS OF OBJECTS. INSIDE CALIPERS MEASURE HOLE
DIAMETERS AND DISTANCE BETWEEN SURFACES. A DIVIDER
CALIPER, POPULARLY CALLED A COMPASS, IS USED TO MARK
OUT LOCATIONS.

THE CALIPER CONSISTS OF TWO LEGS HINGED AT TOP AND
THE ENDS OF LEG SPAN THE PART TO BE INSPECTED. THIS
SPAN IS MAINTAINED AND TRANSFERRED TO THE SCALE.
TYPES OF CALIPERS:
a) FIRM JOINT CALIPER
b) SPRING CALIPER
CALIPER

INSIDE CALIPER OUTSIDE CALIPER DIVIDER CALIPER
SPRING CALIPERS

TELESCOPIC GAUGE
TELESCOPIC GAUGE IS
USED FOR THE
MEASUREMENT OF
INTERNAL DIAMETER OF A
HOLE DURING MACHINING
OPERATION.

DEPTH GAUGE
A DEPTH GAGE IS A VERY COMMON HAND TOOL USED TO INSPECT THE DEPTH OF
HOLES, SLOTS, RECESSES OR THE DISTANCE FROM ONE SURFACE TO ANOTHER.

PRECISION MEASURING INSTRUMENT
o VERNIER CALIPER
o VERNIER HEIGHT GAUGE
o VERNIER DEPTH GAUGE
o OUTSIDE MICROMETER
o INSIDE MICROMETER
o VERNIER MICROMETER
o SLIP GAUGES
o DIAL INDICATOR
o COMPARATORS

VERNIER CALIPER
PRINCIPLE:
WHEN TWO SCALES OR DIVISION SLIGHTLY DIFFERENT IN SIZE ARE USED,
THE DIFFERENCE BETWEEN THEM CAN BE UTILIZED TO ENHANCE THE
ACCURACY OF MEASUREMENT. VERNIER CALIPERS ARE PRECISION
MEASURING INSTRUMENTS THAT GIVE AN ACCURACY OF 0.1 MM TO 0.01
MM.

VERNIER CALIPER
CONSTRUCTION:
 THE VERNIER CALIPER CONSISTS OF TWO SCALES , ONE IS FIXED AND THE OTHER IS MOVABLE.
 THE FIXED SCALE CALLED MAIN SCALE IS CALIBRATED ON L SHAPED FRAME AND CARRIES A FIXED JAW.
 THE MOVABLE SCALE CALLED VERNIER SCALE AND CARRIES A MOVABLE JAW.
 WHEN THE TWO JAWS ARE CLOSED, THE ZERO OF THE VERNIER SCALE COINCIDES WITH THE ZERO OF
THE MAIN SCALE. FOR PRECISE SETTING OF THE MOVABLE JAW, AN ADJUSTMENT SCREW IS PROVIDED.
 ALSO, AN ARANGEMENT IS PROVIDED TO LOCK THE SLIDING SCALE ON THE FIXED MAIN SCALE.

USES OF VERNIER CALIPER
VERNIER CALIPERS ARE EMPLOYED FOR BOTH INTERNAL AND EXTERNAL MEASUREMENT. IT
IS GENERALLY USED BY CLOSING THE JAWS ON TO THE WORK SURFACE AND TAKING THE
READINGS FROM THE MAIN SCALE AS WELL AS THE VERNIER SCALE.
Reading = M.S + V.S*(L.C)
= 23 + 20 * (0.02)
= 23 + 0.4
= 23.4mm
L.C = Value of
smallest
division on
M.S / total
division on V.S
= 1 / 50
= 0.02mm

LEAST COUNT
IT IS THE CAPABILITY OF AN INSTRUMENT TO MEASURE MINIMUM DISTANCE
ACCURATELY.
THE LEAST COUNT IS THE DIFFERENCE BETWEEN THE VALUE OF MAIN SCALE DIVISION
AND AUXILIARY SCALE DIVISION.
L.C = VALUE OF SMALLEST DIVISION ON MAIN SCALE / NO. OF DIVISION ON
AUXILIARY SCALE

VERNIER DEPTH GAUGE
VERNIER DEPTH GAUGE IS USED TO MEASURE THE DEPTHS OF HOLES, SLOTS AND
RECESSES AND DISTANCES FROM A PLANE SURFACE TO A PROJECTION.
PARTS OF VERINER DEPTH GAUGE:
FOLLOWING ARE THE DIFFERENT PARTS OF VERNIER DEPTH GAUGE:
MAIN SCALE
VERNIER SCALE
LOCKING SCREW
FINE ADJUSTMENT SCREW
MOVABLE HEAD
MEASURING FACE

DIGITAL VERNIER DEPTH GAUGE
DIAL VERNIER DEPTH GAUGE

CONSTRUCTION:
A SLIDING HEAD HAVING FLAT AND TRUE BASE FREE FROM CURVES AND
WAVINESS.
 THE GRADUATED BEAM KNOWN AS MAIN SCALE. THE SLIDING HEAD
SLIDES OVER THE GRADUATED BEAM.
 AN AUXILIARY HEAD WITH A FINE ADJUSTMENT AND A LOCKING SCREW.

VERNIER HEIGHT GAUGE
PRINCIPLE :- IT WORKS ON THE PRINCIPLE OF DIFFERENCE BETWEEN TWO DIFFERENTLY
GRADUATED SCALES.
USE :- PRECESSION MARKING AND MEASUREMENT OF HEIGHT
PARTS :- 1.BASE
2. BEAM/MAIN SCALE
3. FINE ADJUSTMENT SCREW
4. SCRIBER
5.VERNIER SLIDE
6. LOCKING SCREWS

CONSTRUCTION
A FINELY GROUND AND LAPPED BASE. THE BASE IS MASSIVE AND ROBUST IN
CONSTRUCTION TO ENSURE RIGIDITY AND STABILITY.
 A VERTICAL GRADUATED BEAM OR COLUMN SUPPORTED ON A MASSIVE BASE.
 ATTACHED TO THE BEAM IS A SLIDING VERNIER HEAD CARRYING THE VERNIER SCALE
AND A CLAMPING SCREW.
AN AUXILIARY HEAD WHICH IS ALSO ATTACHED TO THE BEAM ABOVE THE SLIDING
VERNIER HEAD. IT HAS FINE ADJUSTING AND CLAMPING SCREW.
A MEASURING JAW OR A SCRIBER ATTACHED TO THE FRONT OF THE SLIDING VERNIER.

MICROMETER
PRINCIPLE:- THE MICROMETER WORKS ON THE PRINCIPLE OF SCREW AND NUT. THE LINEAR MOVEMENT
OF THE SPINDLE DURING ONE ROTATION IS EQUAL TO THE PITCH OF SCREW.
PARTS:-
• FRAME
• ANVIL
• SPINDLE
• SLEEVE/BARREL
• THIMBLE
• RATCHET
• LOCK

OUTSIDE MICROMETER
 THE MICROMETER REQUIRES THE USE OF AN ACCURATE SCREW THREAD AS A MEANS OF OBTAINING A
MEASUREMENT.
 THE SCREW IS ATTACHED TO A SPINDLE AND IS TURNED BY MOVEMENT OF A THIMBLE OR RATCHET AT
THE END.
 THE BARREL, WHICH IS ATTACHED TO THE FRAME , ACTS AS A NUT TO ENGAGE THE SCREW THREADS,
WHICH ARE ACCURATELY MADE WITH A PITCH OF 0.5 MM.
 EACH REVOLUTION OF THIMBLE ADVANCES THE SCREW 0.5 MM.
 ON THE BARREL A DATUM LINE READS IN MM, AND THE SET ABOVE THE LINE READS IN HALF MM.
 THE THIMBLE SCALE IS MARKED IN 50 EQUAL DIVISIONS, FIGURED IN FIVES, SO THAT EACH SMALL
DIVISION ON THE THIMBLE REPRESENTS 0.01MM.

WORKING
 The thimble is rotated till the spindle touches the work piece. Then the final adjustment is
made by using ratchet.
 The locknut is then tightened and the dimension is measured on main scale and thimble scale.
PRECAUTIONS & CARE
 Clean the measuring surface of anvil before use.
 Check the instrument for zero reading before use.
 While taking measurements, pressure applied on thimble must be correct. Use ratchet for final
adjustment of pressure.

Reading
= M.S + (T.S. * (L.C))
= 13.5 + (13 * 0.01) mm
= 13.5 + 0.13.
= 13.63mm
Reading
= M.S + (T.S. * (L.C))
= 7 + (31 * 0.01) mm
= 7 + 0.31
= 7.31mm

INSIDE MICROMETER
THE INSIDE MICROMETER IS USED TO MEASURE THE INTERNAL DIMENSIONS OF WORK PIECE.
CONSTRUCTION:-
 IT IS SIMILAR TO THE OUTSIDE MICROMETER. HOWEVER INSIDE MICROMETER HAS NO U SHAPE
FRAME AND SPINDLE.
 THE MEASURING TIPS ARE CONSTITUTED BY JAWS WHOSE FACES ARE HARDENED AND GROUND TO A
RADIUS.
 THE ONE OF THE JAW IS HELD STATIONARY AT THE END AND SECOND MOVES BY THE ROTATION OF THE
THIMBLE.
 THE LOCKING ARRANGEMENT IS PROVIDED WITH FIXED JAW.

Screw Thread Micrometer
The shape of a Screw thread Micrometer is more or less like an ordinary
micrometer with the difference that it is equipped with a pointed spindle
and a double V-anvil, both correctly shaped to contact the screw thread of
the work to be gauged.

METROLOGY.for engineering students 5th sem

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