linear_measurement_metrology_explanation.pdf

Brief Explanation on the topic Linear Measurement of Subject Metrology.

1. EngineeringMeasurements
LinearMeasurements

2. Introduction
•Measurement of perpendicular distance between two
points or surfaces.
•Applies to measurement of length,heights, diameters,
thickness, radiusetc.
•Linemeasuringinstrumentsconsistsofseriesofaccurately,
spacedpaintedormarkedlinesonthem

3. Introduction
(A) Classification based on methods ofmeasurement
l. Direct measuringinstruments.
2.Indirect measuringinstruments.
•Measuringinstrumentscanbefurtherclassifiedas:
(a)Graduated instruments: It includes rulers, vernier callipers,
vernier height gauges, vernier depth gauges, micromèters,
dial indicators etc.
(b)Non-graduated instruments : It includes callipers, wire
gauges, screw pitch gauges, radius gauges, thickness
gauges, slip gaugesetc.

4. Graduated instruments

5. Non-graduated instruments
Callipers
Wiregauges Screw pitchgauges

6. Surface Plate
A surface plate is a hard, solid and
horizontal flat plate, which is used as
areference plane for precision
inspection, marking out and precision
tooling setup.
Since surface plate is used as the
datum for all measurements on a
job, it should be finished to a high
degree ofaccuracy.
The surface plates are made either
from cast iron or granite.

7. V ‐ Blocks
V‐blocks are extensively used for inspection of jobs with circularcross‐section.
The cylindrical surface rests firmly on the sides of the ‘V’ and the axis of the job
will be parallel to both the base and sides of theV‐block.
Generally, the angle of the V is 90
0
, though 120
0
angle is preferred in some cases.
It is made of high grade steel, hardenedabove 60 HRC and ground to a high
degree ofprecision.

8. •Callipers are used for measurement of the parts,which
cannot be measured directly with thescale.
•The calipers consist of two legs hinged at top, andthe ends
of legs span part to beinspected.
•Callipers are of two types: spring type and firmjoint type.
Callipers

9. Spring Type Callipers
The two legs are attached with spring in these type of calipers.
The working ends of each leg of a spring calipers should be
identical in shape and have contact points equally distant
from thefulcrum.
The top portion of the legs are located in a flanged fulcrum
roller and held in position by a spring in order to maintain the
alignment of the working ends.
The spring provides sufficient tension to hold the legs rigid at
all points of theadjustment.

10. Spring type caliperstypes
Outside SpringCallipers
Designedto measure outsidedimensions.
The accuracyin calipermeasurement
depends upon theinspectorssense of
feel.
The legs are held firmly against the end
of the proper dimensionsby adjusting
nut with the thumb andforefinger.
A steel rule must be used in conjunction
with them if a direct readingis desired.

11. Spring type calipersTypes
Inside SpringCalipers
They are designed to measure the
inside dimensions.
It is exactly similar to an outside
caliper with its legs bent outward.
Adjustment in them is generally
made by knurled solid nut.
They are used for comparing or
measuring hole diameters, distances
between shoulders, or other parallel
surfaces of any inside dimensions.
To obtain a specific reading, steel
scale must be used as with the
outside calipers.

12. Firm Joint Type Callipers
They work on the frictioncreated at the junction of the legs.
The two legs are identical in shape with the contact points
equally distant from the fulcrum joined together by a rivet.
The distance between the rivet center and the extreme
working ends of the legs is called nominal size and are
available in the nominal size of 100, 150, 200 and 300 mm.
Firm joint calipers are of following types:
(i)Outsidecaliper
(ii)Insidecaliper
(iii)Transfercaliper
(iv)Hermaphroditecaliper

13. Firm Joint Callipers Types
Outside Firm Joint Caliper
Unlike spring type outside calipers, it does
not have anyspring.
The construction is quite simple with two
identical legs held firmly bythe fulcrum.
If direct reading is desired, a steel rule
must be used in conjunctionwith them.
Inside Firm Joint Caliper
Inside firm joint calipers are almost similar
to inside spring type caliper with the
exception that it does not have any spring
to hold the legs.

14. Firm Joint Callipers Types
Hermaphrodite Caliper
It is also known as odd leg caliper
consisting of one divider and one
caliper leg.
It is used for layout work like scribing
lines parallel to the edge of the work
and for finding the center of a
cylindrical work.
It can be with two types of legs, viz.
notched leg or curved legs.

15. Gauges
LimitGauges
•In component manufacture we use tolerances in
dimensions. For example the diameter of a hole,the
minimum and maximum values acceptable are
20mm –0.02mm ( 19.98mm) and 20mm + 0.02mm
(20.02mm)
•Limit gauges are used for checking limits of the
dimension of thecomponent.
•The “Go gauge” should pass through thehole
while “Not Go gauge” should not pass throughthe
hole.

16. Gauges
RadiusGauges
A radius gauge is a hand-held tool which has many precision rounded
curves (radii) machined into its edges. This is also referred to as a fillet
gauge.
Common metric gauges provide measuring ranges from: (0.75 -5 mm)
18 blades with 0.25 mm increments or(5.5 -13 mm) 16 blades with
0.5 mmincrements

17. Gauges
Thread gauge (Screw threadgauge)
Thread gauges are used to check the pitch of screwthreads
Screw pitch gauge has several leaves.The leaves are clearly imprinted
with the size and are used to determine the pitch of variousthreads.

18. Gauges
Wiregauge
Wire gauges are reference tools used for selecting the appropriate diameter
of thewire for a specificpurpose.
Wire diameter size is given by
British standard Wire Gauge
(SWG)No.

19. Gauges
FeelerGauge
A feeler has a number of folding metal strips (also known as blades)
which are machined to specified thicknesslevels.
The gauge gives you an idea of how wide a gap is by physically filling
the space with metal strips which have a known thicknessvalue.
Feeler gauges can take measurements as small as 0.02mm and as
large as 5.08mm.

20. Linear Measuringinstruments
(B) Classification based on the accuracy that can beobtained
l. Non-precision type instruments : It includes steel rule,
calliper, divider, depth gauge etc.
2. Precision type instruments : It includes vernier calliper,
vernier height gauge, vernier depth gauge, micrometer,
slip gauges,etc.

21. LeastCount
•Capability of an instrument to measure minimum
distanceaccurately.
•It represent the accuracy ofmeasurement
•Difference between the value of main scale division and
auxiliary scaledivision.
Least count of Vernierinstruments
L.C. of vernier instruments also canbe
calculatedas

22. LeastCount

23. Least count of micrometer

24. Vernier calliper
Vernierprinciple:Whentwoscales(mainandauxiliaryscales)
ordivisionslightlydifferentinsizeareused,thedifference
betweenthemcanbeutilizedtoenhancetheaccuracyof
measurement.
Construction:

25. Vernier calliper
Working

26. Uses

27. TypeA:
Vernier has jaws on both sides for external and internal measurements
and a blade for depth measurement.
Types of Vernier Callipers

28. TypeB:
It is provided with jaws on one side for external and internal
measurements.
Types of Vernier Callipers

29. TypeC:
It has jaws on both sides for making the measurement and for
marking operations.
Types of Vernier Callipers

30. Errors in vernier calliper
1.Errorsduetoplaybetweentheslidingjawandfixed
scalebar.
2.Errorduetowearandwrappingofjaws.
3.Errorsduetoincorrectobservationofscalereadings
4.Errorsduetoexcessiveforceonmovingjaw.
5.Errorisalsointroducedifthelineofmeasurement
doesnotcoincidewiththelineofthescale

31. Vernier Height Gauge
Similar to a vernier caliper
except that the fixed jaw in
this case is replaced by a
fixed base which rests on a
surface plateor table when
taking measurements.

32. 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.

33. Micrometers
•Usefuldeviceformagnifyingsmallmeasurement
•Micrometersworksontheprincipleofscrewandnut.Thescrew
isattachedtoaconcentriccylinderorthimble,thecircumference
ofwhichisdividedintoanumberofequalparts.Whenascrewis
turnedthroughnutbyonerevolution,itsaxialmovementisequal
topitchofthethreadofscrew.

34. Micrometers

35. Parts of Micrometer
•Spindle:Thecylindricalcomponentwhichmoveswhenyourotatethe
thimble.Thistouchestheobjectwhichistobemeasuredandholdsittight.
•Anvil: Spindle moves towards the anvilin order to hold the object and take out
themeasurement.
•Lock Nut: This is used to tighten the movement of the spindle so that it doesn’t
move while taking themeasurement.
•Thimble: It is the component which is turned by thumbs whichmakes the spindle
movement.
•Ratchetknob:Thedevicewhichisattheendoftheinstrumentandis
responsibleforexertingonlyallowablepressuretotheobjectandnotmore
thanthat.

36. Micrometers

39. Types ofmicrometer
InsideMicrometer
DepthMicrometer
OutsideMicrometer
ThreadMicrometer

40. Inside Micrometer

41. Depth Micrometer

42. Vernier Micrometer
•In order to increase accuracy, the vernier principle can be
applied to the outsidemicrometer
Mainscaleisgraduatedonthebarrelwithtwosetsofdivisionmarks.Theset
belowthereferencelinereadsinmmandsetabovethelinereadsin1/2mm
(0.5mm).
Thimble scale is graduated on thimble with 50 equaldivisions.
•Each small division of thimble represents 1/50 of minimum division of
mainscale.
•Main scale minimum division value is ½ mm (0.5mm). Henceeach
division of thimble is equalto 0.5/50 = 0.01mm.

43. Vernier Micrometer
•Vernierscaleismarkedonbarrel.Thereare“l0divisions
onbarrelandthisisequivalentto9divisionsonthe
thimble.”
•Hencedivisiononvernierscaleisequalto9/10thatof
thimble.
•Butonedivisiononthimbleisequalto0.01mm.
Therefore,onedivisiononvernierscaleequalsto

44. Vernier Micrometer

45. Vernier Micrometer

46. Slipgauges
•They can be used to measure tolerances in the range of 0.001
to 0.0005 mm veryaccurately.
•Slip gauges are the universally accepted ‘standard of length’ in
industries. These are the simplest possible means of measuring
thelinear dimensions veryaccurately.
•Slip gauges are rectangular blocks of high grade hardened steel
having a cross-section of about 30 by 10 mm manufactured with
very highdegree of finish, flatness and accuracy.

47. Slipgauges
Grades of Accuracy of SlipGauges:
•Slip gauges are made in five grades ofaccuracy.
–Calibration grade, grade 00, grade 0, grade I, and gradeII,
in the decreasing order ofaccuracy.
•Grade 0, grade I, grade II are used for general
workshop purpose and are known as working gauge
blocks.
•Calibration grade (master gauge blocks) and grade
00 (Inspection gauge blocks) are used only for
checking other types ofblocks.

48. Slipgauges
Slip GaugesSets:
Gauge blocks are available in sets with the steps of 10, 1, 0.1,
0.01 and 0.001mm.
Some available Metric (mm) setsare:

49. Applications Slipgauges
•Slip gauges are usedfor
–checking the accuracy ofverniercalipers,micrometers
and other measuringdevices
–setting the comparators toaspecificdimensions.
–directprecisemeasurementwhere the accuracy ofwork
pieceisimportant
–measuringangle of work pieces with sinebar
–checking the gapbetweenparallellocations