metrology and measurements Fundamentals to understand

Basic Metrology and measurements like introduction and Terminology to understands.

1. METROLOGY
1 2 3 4 5 6 7 8 9
Fundamentals of Measurement

2. Metrology
Metrology .
In view of measurement , I have taken up an initiative to illustrate briefly
some of the important aspects which people usually come across during
measurement and instrument handling. The effort shows various
methodologies , terminologies with their practical importance . I have also
catered various methods in which measurement errors/confusions are
observed , my motive is to show / illustrate easy way of catering measuring
fundamentals and their proper usages . I have tried to cover major points
which are usually observed in mass production related to reading drawings ,
understanding , drafting , providing decisions and handling of various
instruments. This chapter contracts emphasis on “Basic fundamentals” of all
measuring methodologies , their interferences with structural drawings
covering all nomenclatures which indirectly are related with any
measurement.
Hope this effort will help and support in production and quality related issues .
PREFACE

3. Angular Measurements
MetrologyMeasurement
Lucknow
Units Measurement
Limit Fit & Tolerance
Geometrical Symbol & Charts
Different Measuring Instruments
Screw Thread measurements
Measurement Terminology
Introduction
Metrology

4. The Greek philosopher Zeno proposed the idea that between
any two points in space there is a distance divisible by an
infinite number of progressively smaller units. His contention
was that it is impossible to traverse an infinite number of units,
and therefore impossible to know the distance between any
two points. This became one of the now famous “Zeno,s
Paradox.”
Like most human inventions, measurement was born out of
necessity-specifically, the necessity to record and relate
information about products, places, or parcels of land. At
inception, it was based on measuring instruments most readily
available to everyone-the parts of the body. This is still
discernible from the name of some of units of measurement
e.g. foot, hand and span.
Metrology

5. The development of measurement system has been refined in two
predominant systems- the Metric System and the English System.
English system is used by United States & few other nations where as
Metric system is used by most of nations in the world.
The current inch and meter are both based on a multiple of wavelengths
of monochromatic light. For example meter is equal to 1,650,763.73
wavelengths in a vacuum of the orange-red radiation of Krypton-86.
Table next gives the Latin prefixes for the metric system & their
equivalent amount of the associated unit. The same prefixes are used for
weight (grams), liquid (liter) and linear (meter).
Metrology

6. Metrology
Metric Prefixes Symbol Multiples and Submultiples Factor
Exa E 1,000,000,000,000,000,000 10
18
Peta P 1,000,000,000,000,000 10
15
Tera T 1,000,000,000,000 10
12
Giga G 1,000,000,000 10
9
Mega M 1,000,000 10
6
Kilo k 1,000 10
3
Hecto h 100 10
2
Deca da 10 10
Deci d 0.1 10
-1
Centi c 0.01 10
-2
Milli m 0.001 10
-3
Micro µ 0.000001 10
-6
Nano n 0.000000001 10
-9
Pico p 0.000000000001 10
-12
Femto f 0.000000000000001 10
-15
Atto a 0.0000000000000000001 10
-18
Unit Prefixes
Metric Prefixes Symbol Multiples and Submultiples Factor
Exa E 1,000,000,000,000,000,000 10
18
Peta P 1,000,000,000,000,000 10
15
Tera T 1,000,000,000,000 10
12
Giga G 1,000,000,000 10
9
Mega M 1,000,000 10
6
Kilo k 1,000 10
3
Hecto h 100 10
2
Deca da 10 10
Deci d 0.1 10
-1
Centi c 0.01 10
-2
Milli m 0.001 10
-3
Micro µ 0.000001 10
-6
Nano n 0.000000001 10
-9
Pico p 0.000000000001 10
-12
Femto f 0.000000000000001 10
-15
Atto a 0.0000000000000000001 10
-18

7. Angular Measurements
Angle: The area between two converging lines.
Units: There are three Units of angle is used
1. Degrees
2. Radians
3. Grads
Degrees: The degree is equal to 1/360 of a complete circle. This is further sub divided into minutes & seconds. e.g.
1°(Degree) = 60’ (Minutes)
1’=60” (Seconds)
Conversion form degree to Degree, Minute & Seconds. (e.g. if the value is in 36.8275° & you need to convert it in Degree, Minute & Seconds)
Step-1 Keep the digit before decimal aside & label it with degree i.e. 36°---------------------------------a
Step II Subtract the “a” from main value i.e. 36.8275-36=0.8275.--------------------------------------------b
Step III Multiply “b” with 60 to get the minute i.e. 0.8275x60=49.65------------------------------------------c
Step IV Keep the digit before decimal aside & label it with minute i.e. 49’---------------------------------d
Step V Subtract the “d” from “c” i.e. 49.65-49=0.65-----------------------------------------------------------e
Step VI Multiply “e” with 60 to get second & round the digit & label it as seconds i.e.0.65X60=39 ------f
36.8275°= 36°49’39” (a°d’f”)
Metrology

8. Conversion form DMS to Degree:
For example convert 30°30’30” in Degree
Step I - Keep the Degree aside i.e 30-----------------------------a
StepII- Divide minutes with 60 i.e.30÷60=0.5------------------b
StepIII-Divide Seconds with 3600 i.e. 30÷3600=0.008333---c
Step IV-Add a+b+c i.e.30+0.5+0.0083=30.508333
Note : Take digit up to 6 digit after decimal.
Radian: The radian is equal to an arc which is the same length as the radius it is projected from. For
example if the radius of an arch is 50 mm & length of the arc is 50 mm then it will be 1 radian.
1 radian is always equal to 57.2958°
To Convert Degree to radian , divide the degree value by 57.2958.
To Convert Radian to Degree multiply the radian value is multiplied by 57.2958.
Grads:
This is less common in use. This is very similar to the degree, with two exceptions. First there are 400
grads in a complete circle instead of 360 as in degrees. Grads have no sub units. This is always expressed
in decimal forms.
To convert grads to degree multiply by 0.9 (360÷400)
To convert degree to grad multiply by 1.111 (400÷360)
Metrology

9. Selection of Instruments for measurements:
There are many measuring instruments, some are different in function
& some are different in degree of accuracy. Those with the least degree
of accuracy are most frequently used.
N.B: Instruments those are least accurate does not means they are
inaccurate.
General thumb rule is that instruments used for measurements should
have the resolution up to 1/10
th
of the tolerance.
Metrology

10. Tolerance
Tolerance is the total amount a dimension may vary. It is the
difference between the maximum and minimum limits.
Ways to Express:
1.Direct limits or as tolerance limits applied to a dimension
2.Geometric tolerances
3.A general tolerance note in title block
4.Notes referring to specific conditions
Metrology

11. Metrology
1. Direct limits and tolerance values
Metrology

12. 1. Direct limits and tolerance values – Plus and Minus
Dimensions
Metrology

13. Geometric Tolerance System
Geometric
dimensioning and
tolerancing (GD&T) is
a method of defining
parts based on how
they function, using
standard ANSI
symbols.
Feature Control Frame
Concentricity
Symbol
Metrology

14. Important Terms – single part
•Nominal Size – general size, usually expressed in common fractions (10
mm for the slot)
•Basic Size – theoretical size used as starting point (.500” for the slot)
•Actual Size – measured size of the finished part (.501” for the slot)
10.015 Upper Limit (MMC)
9.990 Lower Limit (LMC)
10.002 – Actual Measured
Dimensions
Metrology

15. Metrology
•Limits – maximum and minimum sizes shown by tolerances (.502 and .498
– larger value is the upper limit and the smaller value is the lower limit, for the
slot)
•Tolerance – total allowable variance in dimensions (upper limit – lower
limit) – object dimension could be as big as the upper limit or as small as the
lower limit or anywhere in between
10.015 Upper Limit (MMC)
9.990 Lower Limit (LMC)
10.002 – Actual Measured
Dimensions
Metrology

16. Metrology
Important Terms – Multiple Parts
•Allowance – the minimum clearance or
maximum interference between parts
•Fit – degree of tightness between two parts
–Clearance Fit – tolerance of mating parts always
leave a space
–Interference Fit – tolerance of mating parts always
interfere
–Transition Fit – sometimes interfere, sometimes clear
Metrology

17. Metrology
Fitting Multiple Parts
Part A
Tolerance of A
Part B
Tolerance of B Fit Tolerance:
Clearance or
Interference
Metrology

18. Fitting Multiple Parts
Metrology

19. Metrology
Shaft and Hole Fits
Metrology

20. Shaft and Hole Fits
CLEARANCE FIT
+ .003
Metrology
CLEARANCE FIT
+ .003
CLEARANCE FIT
+ .003
CLEARANCE FIT
+ .003

21. Basic Hole System or Hole Basis
•Definition of the "Basic Hole System":
The "minimum size" of the hole is equal to
the "basic size" of the fit
•Example: If the nominal size of a fit is 1/2", then
the minimum size of the hole in the system will
be 0.500"
Metrology

22. Metrology
Basic Hole System
•Clearance = Hole – Shaft
•Cmax = Hmax – Smin
•Cmin = Hmin – Smax
Both Cmax and Cmin >0 – Clearance fit
Both Cmax and Cmin <0 – Interference fit
Cmax > 0 Cmin < 0 – Transition fit
•System Tolerance = Cmax – Cmin
•Allowance = Min. Clearance = Cmin
S
MAX
S
MIN
H
MAX
H
MIN
Metrology

23. Basic Hole System – Example
4.90
4.85
5.10
5.05
Calculate Maximum and Minimum Clearance
Clearance = Hole – Shaft
Cmax = Hmax – Smin
Cmax = 5.10 – 4.85 = 0.25
Cmin = 5.05 – 4.90 = 0.15
What is Type of Fit?Cmax > Cmin > 0 Clearance
Metrology

24. Metric Limits and Fits
•Based on Standard Basic Sizes – ISO
Standard, see the Appendix material
(Table A.2 on pp. A-10 to A-13 in text)
•Note that in the Metric system:
Nominal Size = Basic Size
•Example: If the nominal size is 8, then the
basic size is 8
Metrology

25. Metric Preferred Hole Basis System of Fits
Metrology

26. Metrology
Metric Tolerance Homework
– Example TOL-1B
Metrology

27. Determining the limits of size for a shaft ø40g11
Basic size step: 30 to 50 mm (from table 4-IS919)
Standard tolerance = 160µm (from table 1-IS919)
Fundamental deviation = -9µm (from table 2-IS919)
Upper deviation = Fundamental Deviation = -9µm
Lower Deviation = Fundamental Deviation – Tolerance
= -9 – 160 µm = -169 µm
Limits of Size:
Maximum = 40 – 0.009 = 139.991 mm
Minimum = 130 – 0.169 = 39.831 mm
Metrology

28. Determining the limits of size for a hole 130N4
Basic size step: 120 to 180 mm (from table 4-IS919)
Standard tolerance = 12µm (from table 1-IS919)
Fundamental deviation = -27 + µm (from table 3-IS919)
Value of D = 4 µm (from table 1-IS919)
Upper deviation = Fundamental Deviation
= -27 + 4 = -23 µm
Lower Deviation = Fundamental Deviation – Tolerance
= -23 – 12 µm = -35 µm
Limits of Size:
Maximum = 130 – 0.023 = 129.977 mm
Minimum = 130 – 0.035 = 129.965 mm
Metrology

29. Metrology
Metrology

30. Metrology

31. Metrology

32. Metrology
Metrology

33. Metrology
Metrology

34. Metrology

35. Metrology
Metrology

36. Metrology

37. Metrology

38. Metrology

39. Metrology

40. Metrology
Metrology

41. Metrology

42. Metrology
Metrology

43. Metrology

44. Metrology
Metrology

45. Metrology
Micrometers: Nomenclature
Metrology

46. Metrology
Slip Gauge:
Accuracy Grades & Applications:
There are five grades of slip gauges are in use:
Grade ’00’: This is the highest grade and is intended for use as
reference only in specialized calibration laboratories.
Grade ‘0’: These higher accuracy gauges are used within controlled
environment & temperature for precision work, like calibration of
slip gauges, instruments, dial gauges & other gauges.
Metrology

47. Metrology
Slip Gauge:
Grade ‘K’: They are used as master of calibration of gauge block
by comparison method in environmentally controlled room.
Grade ‘1’: This is normal grade for use within designated
inspection area for inspection of equipment such as Plug Gauges,
Limit Snap Gauges, Setting of electronic measuring devices,
Verniers, Micrometers etc.
Grade ‘2’: This is normal inspection grade used in shop floor for
general inspection.
Metrology

48. Metrology
Slip Gauge:
Care for Slip Gauges:
•Never use slip gauge bare hand (Put on cotton gloves).
•After the work is over remove finger print over the working face of
gauge block with the help of tissue paper & alcohol.
•Apply Petroleum jelly on the Block.
•Always keep the block in the case provided.
•Save the working face from minor scratches too.
Metrology

49. Metrology
Process of Wringing or joining two gauge block together

50. Metrology

51. Metrology
Nomenclature of a Vernier Calliper

52. Metrology
Different uses of Vernier Calliper
Metrology

53. Metrology
Metrology
How to Read Vernier Calliper

54. Metrology
Digital Calliper
Precautions:
•Before taking measurement ensure that at initial position it is showing zero
other press zero at initial (Both jaws closed together).
•For taking internal measurement do not forget to add the jaw width in the
result. Usually it is written on back of the Calliper jaws.)
•Do Not wipe the digital Calliper with oil or any lubricant.
•Keep it in the case provided.
•Store it in moist free environment. (It will be better if you put some bag of
silica jell in the storage cup-board)
Utmost care to be taken to
this surface so that it could
not get scratched/damaged.
Metrology

55. Metrology

56. Metrology
Multi anvil Depth Micrometer

57. Metrology

58. Metrology
Bore Gauge

59. Metrology

60. Metrology
Applications: For general purpose measurement like diameter, length
etc
Digimatic Micrometers

61. Applications: For Span measurements of gears, tooth thickness, undercut
dimensions etc
Metrology
Flange Micrometers

62. Metrology

63. Metrology
Gear Tooth Vernier Calliper
Uses:
For measuring
tooth width,
chordal thickness
or any dimensions
at particular height
or width.

64. For measuring narrow groove, recess slot, web thickness of drill,
keyways & other hard to reach dimensions.
Metrology
Point Micrometer

65. Application:
For measuring groove diameters, recess slot, keyways &
other hard to reach portions.
Metrology
Blade Micrometer

66. Metrology
Application:
This is used for checking circular having odd number of flutes,
Screw Tap, End mill.
Geometrical form such as lobbing etc.
Prismatic Micrometer

67. Metrology
Inside Micrometer
Application:
For inspection of bore diameter, slot diameter, root diameter etc.

68. Application:
This is a comparator with high degree of repeatability used in
mass inspection of precise components with reference to a setting
master.
Metrology
Dial Snap Meter

69. Metrology
Dial Indicator
The indication of such indicator is
obtained by a gear train. In operation
sensitive contact point is attached with
rack & indicator hand is attached with
pinion gear.
It comes in many combination of
resolution of 0.0005mm to 0.1 mm.

70. Metrology
Metrology
Lever Type Dial Gauge: Taking measurement with lever
type dial gauge try to keep the axis of contact point parallel or at 90°
to the measuring direction. Other than this reading must be
multiplied by the correction factor as per the given table.

71. Metrology
Metrology
Plain Plug Gauge
This is used for checking limit of minor diameter of holes.

72. Master Setting Ring
Uses: Quick setting of
bore gauge, Inside
micrometers, Air
gauge & as a refernce
master.
Care: Its surface must
be protected from rust,
finger prints, high
humid area & store
with applying
petroleum jelly.
Metrology

73. Metrology
Cylindrical Setting Master
Uses: Used as reference
standard for setting dial snap
gauge, Prismatic micrometers,
dial comparators etc.
Care & Storage: It should be
protected from rust, dust &
should be stored with proper
application of any rust
preventive like petroleum jelly.
Its working surface should not
get scratches.
Metrology

74. Metrology
Metrology
Tri Square
This is most common tool use in shop floor
This is used to check sureness between the
reference surfaces, marking perpendicular line.

75. General Handling Precautions for Instruments/Gauges.
• Do not keep any instruments directly on ground. (Silica present on ground acts as an abrasive & causes
scratches/damages of the base.
•Moisture present on the ground will also cause rusting of the base.
•There should not be much more temperature differences in measuring instruments & work pieces.
(Ideally both should be kept in same temperature/environments at least two hours prior to
measurements.
•Storage of instruments:
•Always keep the instruments in the case provided.
•After the work end of each day keep the gauges (Specially ferrous) after applying thin oil or petroleum
jelly.
•If the gauges are in very rare in use then wipe the old petroleum jelly every month with help of Carbon
tetra Chloride (CCl
4
) then again apply the jelly.
•Do not oil the plunger of Dial Indicator.
•Do not oil the Surface of Digital Vernier Calliper.
•Do not dismantle any parts if any problem you face the with measuring instruments (Better hand over
this instruments to metrology personnel mentioning the problem).
•Do nor replace the parts of one instrument with the other.
Metrology

76. Precautions for Digital Micrometers:
1.Do not dismantle any parts.
2.The spindle is designed so that it can not be removed from the inner sleeve. Do not move it past the
upper limit of the measuring range.
3.Do not use electric marking pen or other such device on the micrometers.
4.Keep the micrometers away from direct sun light.
5.Keep the micrometers away from dirt, dust or moisture.
6.Always keep in the case provided.
7.Avoid taking measurement when job is wet with oil or coolant.
8.While storing only external or exposed area of spindle to be wiped with the linen free cotton clothe
soaked with thin oil & ensure that before rotating this oil must be cleaned with dry cloth & alcohol.
9.Always hold the micrometers on the insulator provided.
10.Measurement must be taken using ratchet force of micrometers.
11.Ratchet should not move more than two turn.
Metrology

77. Sin length=300 m
m
G
a
u
g
e

b
l
o
c
k

h
e
i
g
h
t
Metrology
Sine Bar

78. Metrology
Measuring angle with the help of sine bar
Step -1 Place the tapered components on the sine bar
Step -2 Raise the one side of sine bar against the taper with the help of Slip gauge.
Step -3 By checking with test indicator make the tapered portion parallel to surface plate by adding removing
slip gauge of different size.
Step -4 If the tapered portion gets parallel to the surface plate, calculate its angle by the formulae-
Sine Angle Sine α = Slip Gauge height (p) ÷ Sin length (h)-Often inscribe on the sine bar.
sine α = p/h
Metrology

79. Table: Permissible deviation for linear dimensions except for broken edges
Tolerance Class
Over
0.5
up to 3
Over
3
up to
6
Over 6
up to
30
Over
30
up to
120
Over
120
up to
400
Over
400
up to
1000
Over
1000
up to
2000
Ove
r
200
0
up
to
400
0
Designati
on Description
f fine ± 0.05± 0.05± 0.1± 0.15± 0.2 ± 0.3± 0.5-
m medium ± 0.1± 0.1± 0.2± 0.3 ± 0.5 ± 0.8± 1.2± 2
c coarse ± 0.2± 0.3± 0.5± 0.8 ±1.2 ± 2 ± 3± 4
v very coarse - ± 0.5±1 ±1.5 ±2.5 ± 4 ± 6± 8
Note: For nominal size below 0.5 mm, the deviation shall be indicated adjacent to the relevant
nominal size's).
Metrology
Open Tolerances for non tolerated linear dimensions

80. Table: Permissible deviation for broken edges (External Radii &
Chamfer Heights)
Tolerance Class
Over 0.5
up to 3
Over 3
up to 6
Over 6Design
ation
Descripti
on
f fine
± 0.2 ± 0.5 ± 1m medium
c coarse
± 0.4 ± 1 ± 2v
very
coarse
Note: For nominal size below 0.5 mm, the deviation shall be indicated
adjacent to the relevant nominal size(s).
Metrology
Open Tolerances for non tolerated external radii & chamfer
heights

81. Table: Permissible deviation for angular dimensions
Tolerance Class Permissible deviations for ranges of lengths, in
millimeters, of the shorter side of the angle concerned
Desig
nation
Descript
ion
Over
10
Over 10
up to 50
Over 50 up
to 120
Over 120 up
to 400 Over 400
f fine
± 1°± 0°30' ±0°20' ±0°10' ±0°5'm medium
c coarse
±1°30
' ±1° ± 0°30' ±0°15' ±0°10'
v
very
coarse±3° ±2° ± 1° ± 0°30' ±0°20'
Metrology
Open Tolerances for non tolerated angular dimensions

82. General Tolerance on Perpendicularity
Tolerance
Class
Perpendicularity tolerances for ranges of
nominal lengths of the shorter side
up to 100
Over 100
up to 300
Over 300
up to 1000
Over 1000
up to 3000
H 0.2 0.3 0.4 0.5
K 0.4 0.6 0.8 1
L 0.6 1 1.5 2
Metrology
Open Tolerances for Perpendicularity

83. Metrology
General Tolerance on Straightness & Flatness
Toleranc
e
Class
Straightness and flatness tolerances for ranges of nominal
lengths
up to 100
Over 10
up to
30
Over 30
up to 100
Over 100
up to 300
Over
300
up to
1000
Over
1000
up to
3000
H 0.02 0.05 0.1 0.2 0.3 0.4
K 0.05 0.1 0.2 0.4 0.6 0.8
L 0.1 0.2 0.4 0.8 1.2 1.6
Metrology
Open Tolerances for Straightness & Flatness

84. Metrology
General Tolerances on symmetry (Values in mm)
Toleran
ce
Class
Symmetry tolerances for ranges of
nominal lengths
up to 100
Over 100
up to 300
Over 300
up to 1000
Over
1000
up to
3000
H 0.5
K 0.6 0.8 1
L 0.6 1 1.5 2
Metrology
Open Tolerances for Symmetry

85. Metrology
General Tolerances on circular run-out (Values in
mm)
Tolerance
class Circular run-out tolerances
H 0.1
K 0.2
L 0.5
Metrology
Open Tolerances for Circular Run Out

86. Metrology

87. Metrology

88. Metrology
Roughness
grade Number
Roughness
value Ra(µm)
Roughness Symbol
Old
New
N12 50 ~
N11 25
N10 12.5
N9 6.3
N8 3.2
N7 1.6
N6 0.8
N5 0.4
N4 0.2
N3 0.1
N2 0.05
N1 0.025
Roughness Grade No. & Symbol
N11
N12
N10
N9
N8
N7
N6
N5
N4
N3
N2
N1
Metrology

89. Metrology
Metrology

90. Metrology
Metrology
Vernier Height Gauges
Like the Vernier Calliper, Vernier Height
Gauge consists of a stationary beam and a
movable slide on which a graduated Vernier
scale is mounted. With that a scriber is
mounted.
Measurement is done at the scriber face.
The primary use of height gauge is in the
field of surface plate work. It is commonly
used for marking vertical distances &
measuring step height or marking line at
particular intervals.

91. Metrology
Vernier Depth Gauge
The Vernier depth gauge differ
slightly from the Vernier caliper
& Vernier height gauge in that
Vernier slide assembly remains
fixed with the jaws & main scale
moves up or down.
This is used to check internal as
well as external depth, step height
Etc.

92. Metrology
Metrology
Dial Snap Gauge
This most common instruments used in shop floor in combination
with setting master in inspection of mass production. Particularly for
measuring diameter having fine tolerances.

93. Metrology
Metrology
Feeler Gauge
This is also known as gap gauge. It checks gaps where normal
measuring instruments has difficulties to reach. It comes in
different size up to 1 mm in the step of 0.01 mm

94. Metrology
Bench Centre
This is basically used to check run out,
circularity & concentricity of circular
job. It is used with combination with
dial indicator.

95. Metrology
Surface PlateSurface Plate
A surface plate is a flat plane used as a reference
surface from which final dimensions are taken. It is
made of two different material one is from cast iron
by scrapping the surface & other from Granite by
lapping & polishing.

96. Metrology
Metrology

97. Metrology
Metrology
Screw Pitch Gauge
This is used for checking pitch of external as well as internal
threads.

98. Setting the origin in Digital Micrometers.
(For single spindle)
Before starting measurement check the origin point and set the origin (datum point) by
following the procedure below.
Remove dust and oil from the measuring faces before setting the origin.
Insert the Battery & lock it.
After putting the battery the origin value 25.000 is displayed and “P” flashes on the
LCD.
•Insert the standard length bar & apply the measuring force by turning the ratchet.
•Press the origin button & flashing of “P” will stop.
Now instrument is ready for taking measurements
Metrology

99. Setting the origin in Digital Micrometers.
(For Multi spindle)
Before starting measurement check the origin point and set the origin (datum point) by following the
procedure below.
Remove dust and oil from the measuring faces before setting the origin.
Insert the Battery & lock it.
After putting the battery the preset/origin value 000.000 is displayed and “P” flashes on the LCD.
•Insert the standard length bar & apply the measuring force by turning the ratchet.
•Keep the preset button pressed for certain seconds the 0 will start flashing.
•Press the preset button continuously to get the desired number.
•Hold the preset button hold till the other “0” starts flashing. If you do not need to
•Press the origin button & flashing of “P” will stop.
Now instrument is ready for taking measurements
Metrology

100. Metrology
Video clippings for setting multi spindle micrometers.

101. Metrology
Metrology
There are many different thread forms in use today. An optical
comparator is the easiest method of determining thread form. Profile
gages, if available, and visual methods can also be used. Great care
must be taken as many forms are almost identical. The Acme form
(29 degree included angle) is only 1 degree different from the ISO
Metric Trapezoidal form (30 degree included angle). Many thread
forms such as Unified, Metric ISO and Acme are subject to
published standards while others, including Ballscrew and Worm
threads, are not defined in detail by any standards organizations.
Screw Thread

102. Metrology
Metrology
Thread Pitch
The thread pitch can be measured with a steel rule, or a caliper or
comparator can be used. The thread pitch is the axial distance from
one thread groove to the next. By laying a steel rule down the axis
of a screw and counting the number of thread crests in a given
length, the pitch can be determined by dividing the count into the
length. In the example shown , there are 5 pitches in 1 in. so the
thread pitch is .200 in. Note that the number of threads per inch is
the reciprocal of the thread pitch. A common mistake is to count the
number of threads starting with "one". This will lead to a one pitch
error. Make sure you start with "zero" for the first thread. To double
check your pitch determination, check your pitch determined by
count against your actual pitch measurement.

103. Metrology
Metrology
The hand of the thread can be easily determined by visual inspection.
Simply compare your screw threads with the right hand and left hand
threads illustrated in Figure 45. Most threads are right hand and right hand
is assumed if no left hand designation is specified. Left hand threads are
common on manual drives where clockwise handle rotation raises,
tightens, extends, or creates motion away from the operator. On fine
threads, it may be necessary to lay a small wire in the thread grooves to
determine hand. Matching the angle of lie of the wire with the illustrations
will indicate the hand of thread

104. Metrology
Metrology
Major Diameter
The major diameter can be measured with a micrometer, caliper or steel
rule. Major diameters are generally the first numbers found in thread
designations. A 1/2-10 Acme thread for example, has a major diameter
of .500 in. Care must be taken to measure the major diameter on a section
of the screw thread that is not worn. A worn portion will measure smaller
(or larger if burrs have been rolled up) than the original major diameter.
Therefore, it is good practice to measure the major diameter over the least
used section of the screw.

105. Metrology
Metrology
Minor Diameter
The minor diameter can be determined by direct measurement on an
optical comparator or by measuring the depth of the thread with a depth
micrometer and subtracting twice the measured depth of thread from the
major diameter. When using a comparator to measure the minor
diameter, remember that the reflected image is reversed (except on
modern, image correcting comparators). This means that the bottom of
the shaft is shown at the top of the screen. Often oil from the shaft runs
down and collects on the bottom of the thread grooves increasing the
shadow image. If the oil is not removed, a false (oversized minor
diameter) reading will result.

106. Metrology
Metrology
Pitch Diameter
The pitch diameter is the diameter at which the thread tooth and the thread space are
equal. To accurately measure the pitch diameter requires optical comparator or thread
wires. The optical comparator is the easiest to use as the measurement can be directly
made and no mathematics are necessary. The disadvantage to the optical method is that
the screw must be physically removed from the machine and taken to the comparator.
Also, many small shops may not be equipped with a comparator. Measurement over
thread wires is an attractive alternative to the comparator for measuring pitch diameter.
These measurements can be made directly on the screw. Thread wire measurements are
quite accurate, however, they require the use of mathematical formulas along with
thread form and pitch information to translate the measurement results into the pitch
diameter.

107. Metrology
Metrology
Number of Starts
The number of starts on most threads is one (single start). However, a number of thread including Lead Screw,
and Ball Screw threads may have from 2 to 20 starts or more. Multiple starts are used to increase the lead (linear
advancement per revolution). In most cases, increasing the number of starts is preferable to increasing the pitch
because larger pitches reduce the minor diameter. A small minor diameter decreases the screw stiffness and
makes it more difficult to tap nuts because of the likelihood of the tap breaking during tapping. Also, for the
same lead, increasing the number of starts actually increases the thread contact area when compared to a thread
with the same lead but using fewer starts and a coarser pitch. Close examination of the thread will reveal the
number of starts 9). Simply place a pencil or marker pen in the thread groove and rotate the thread one
revolution. If the end of the pencil mark is in the adjacent thread groove, the screw has a single start. If there is
one thread between the beginning and the end of the mark, it is a two start thread, two grooves, a three start
thread and so on. Another way to discover the thread starts is to examine a transverse section of the screw. As
illustrated in Figure, if the end view is an offset circle, the screw is single start. A two start thread will have
roughly a football shape, a three start thread will have a tri-oval shape and a four start thread will be noticeably
four cornered. Usually, five starts and up can simply be counted in the transverse section.

108. Metrology
Metrology
Identification procedure for threads
Determine if the thread is Taper or Parallel.
With the help of Vernier Calliper measure the tip diameter of 1
st
, 4
th

& last full threads.
If the diameters increases for a male thread or decreases for a female
thread the thread is Taper.
If all the diameters are same the thread is Parallel or straight.
Pitch: In NPT pitch refers to number of thread per inch while in
metric thread pitch refers to distance between adjacent threads.

109. Metrology
Metrology

A taper thread is a continuous helical ridge of uniform section
and uniform axial spacing formed on the exterior or interior of a
circular cone.
In taper screw thread minor, effective & major diameters
progressively increases along the axis, hence there must be
known the following particulars.
•The Taper angle
•The position (usually at the end face) at which it is agreed to
measure effective diameter.

110. Metrology
Metrology
NPT Threads: The National (American) pipe threads has a thread
angle of 60°, and is mainly used for connections where pressure-
tight joints are made on the threads.
BSP Taper Threads (British standard pipe thread): It has a thread
angle of 55°

111. Metrology
Metrology
NPT Thread designation.
The type of pipe threads are designated by specifying in sequence the
nominal pipe size, number of thread per inch and the thread series symbol
as follows.
3/8 – 18 NPT
1/8 – 27 NPSC
½ - 14 NPTR
For left hand thread use suffix LH other wise it will be assumed as right
hand thread.
3/8 – 18 NPT -LH
Major Dia
No. of thread
per inch
TPI
Symbol
Hand

112. Metrology
Metrology
Each these letter in the symbol has a definite significance as
follows:
N = National (American) Standard
P = Pipe
T = Taper
C = Coupling
S = Straight
M = Mechanical
L = Locknut
H = Hose coupling

113. Metrology
Determine the thread pitch
To determine the thread pitch, use the screw pitch gauge and check the
thread against each form until you find a match. Try the appropriate
pitch gauge form for the threads until you find the perfect match as
shown in picture below.
Improper
Matching
Proper
Matching

114. Metrology
Metrology
Number of Starts

115. Metrology
Nomenclature of Taper Thread
Metrology

116. D = Basic major Diameter of internal thread (nominal diameter)
d = Basic major Diameter of external thread (nominal diameter)
D
2
= Basic Pitch Diameter of internal thread
d
2
= Basic Pitch Diameter of external thread.
D1= Basic Minor Diameter of internal thread
d1= Basic Minor Diameter of external thread
H= Height of the fundamental triangle.
P= Pitch
P
Metrology

117. H=0.866025P
D
2
= d
2
= d-3/4H = d-0.64952P
D
1= d
2-2(H/2-H/4) = d-2H1 = d-1.08253P
d
3=d
2-2(H/2-H/6) = d-1.22687P
H
1= (D-D1)/2 = 5/8H = 0.54127P
h
3 = (d-d3)/2 = 17/24H = 0.61343P
R= H/6 = 0.14434P
Formulae for Basic Elements of Screw Thread
Metrology

118. Metrology
Three Wire Set For Inspection of Effective Diameter of Thread
Metrology
M
For Thread Angle 60° : E= M-3d+0.866025P
For Thread Angle 55° : E= M-3.16567d+0.96049P
Where
E= Effective Diameter
M- Dimensions over wire
P- Pitch of the thread

119. Metrology
Metrology
Thread Plug Gauge
Thread Plug gauge are maninly consists of two parts one is GO
& other is NOGO.
GO-Checks the maximum material functional limit. For the
product to be acceptable gauges must enter & freely pass the
whole thread length. It checks all elements of threads except the
minor diameter.
NOGO- Checks the minimum functional limit of effective
diameters.

120. Thread Ring Gauge:
Uses: It is used to check effective
diameter as well as profile of an
external thread. It is of two type one is
GO thread ring gauge which checks
the maximum material limit of an
external threaded parts. For a part to be
acceptable it must freely enter the Go
thread ring gauge to entire length. GO
thread ring gauge checks all the thread
elements except the major dia.
NOGO which checks minimum
material limit of a threaded parts. For
the parts to be acceptable, the gauge
should not enter thread or pass over the
thread more than three turns without
applying excessive force.
Metrology

121. Wear Check Plug Gauge
It is used for checking maximum wear
limit of thread ring gauges. While
checking it should not pass the thread ring
gauge or more than one complete turn with
normal hand pressure.
Care & Storage: It should be protected
from rust, dust & should be stored with
proper application of any rust preventive
like petroleum jelly.
Metrology

122. Metrology
Metrology
Quality Terminology
Accuracy: A general term describing the closeness between measured
value & true value.
Calibration: A determination of the errors of a measuring instruments
or standard.
Datum: A theoretically exact geometric reference to which tolerance
features are related.

123. Metrology
Dimension: A numerical value that defines a features.
Discrimination: The ability of an instruments to respond to small
changes in the measured quantity.
Error: The difference between measured value & true value.
Measured value: The result of a measurement.
Precision: The closeness of agreement between successive
measurements under identical conditions over a short time interval.
Usually defined with a specified probability.

124. Metrology
Metrology
Repeatability: The closeness of agreement between successive
measurements under identical conditions over a short time interval.
Usually defined with a specified probability.
Reproducibility: The closeness of agreement between measurements
under different conditions (different appraiser or different instrument).
Resolution: The ability of an instruments to respond to small changes
in the measured quantity.

125. Metrology
Metrology
Stability: Reproducibility of readings separated by long time intervals.
Traceability: The ability to establish the valid calibration of an
instrument or standard by step by step comparison with better standards.
Uncertainty: The range of value relative to the measured value with
in which the true value is estimated to lie, generally with a specified
probability.

126. Metrology
Metrology
Torque
Torque is the application of a FORCE acting at a radial
DISTANCE and tending to cause rotation.
S.I IMPERIAL METRIC
mN∙m – milli Newton meter.
cN∙m – centi Newton meter.
N∙m – Newton meter
ozf∙in – ounce force inch
lbf∙in – pound force inch
lbf∙ft – pound forces foot
gf∙cm – gramme force centimeter
kgf∙cm – Kilogramme forces centimeter
kgf∙m – Kilogramme force meter

127. Metrology
Metrology
Example: convert 10lbf∙ft into cN∙m = 10*135.6 = 1356 cN∙m
Units to be
Converted
mN∙mcN∙mN∙m ozf∙inlbf∙inlbf∙ftgf∙cmKgf∙cmKgf∙m
1 mN∙m = 1 0.10.0010.1420.0090.000710.20.010.0001
1 cN∙m = 10 1 0.011.4160.0880.0071020.1020.001
1 N∙m = 1000100 1141.68.8510.73810.19710.20.102
1 ozf∙in =70620.7060.00710.06250.005 72 0.0720.0007
1 lbf∙in =11311.30.11316 1 0.0831152.11.1520.0115
1 lbf∙ft =1356135.61.356192 12 1 13.82613.830.183
1 gf∙cm =0.0980.010.00010.0140.00090.00007 1 0.0010.00001
1 Kgf∙cm =98.079.8070.09813.890.8680.0721000 1 0.01
1 Kgf∙m =9807980.79.807138986.87.233100000100 1
TORQUE CONVERSION FACTOR

128. Metrology
Metrology
1. Serial No. : 722
2. Date of Procurement : 1996
3. Date of Commissioning : 1997
4. Make : LEITZ, Germany
5. Model : PMM 12 10 6
6. Measuring range : X = 1200 mm, Y = 1000 mm, Z = 600
7. Linear U1 (µm) (L in mm) : 0.5 + L/700 µ
Volumetric U2 (µm) (L in mm) : 0.8 + L/450 µm
Gauge Accuracy : 0.3 + L/1000 µm
In volume 600 X 600 X 300 mm
8. Minimum resolution : 0. 1  m
9. Probing Speed : 0.1 - 3 mm/sec
10. Max. Scanning Speed : 50 mm/s
11. Air Pressure : 5.5 ± 0.3 bar
12. Max. Probe pin wt. : 650 gm (W/o Probe holder)
13. Pickup of measuring points : 200 points/sec
14. Operating Temperature : 20
0
± 0.5
0
C
CMM

129. Metrology
Metrology
Software
•GRAPHIC Programming (GRABAS)
• Form Analysis, Basic Statistics (STCBAS),
•Quality Control Charts (STCGCC),
• Machine capability test (STCMCS),
• Trend Analysis (STCTRO),
• Measurement of Helical & Spur Gear (GEARHX),
• Measurement of Involutes Bevel Gear (GEARBV),
• Measurement of Straight Bevel Gear (GEARSB),
• Calculation of basic setting for Gleason (BVMACH),
•Calculation of nominal Bevel Gear Tooth profile processing of bevel
(BVCORR),
• Gear measuring data and calculation of correct parameter for Gleason
cutters, 2 Dimensional gauging of a element (hole pattern) to their
nominal position with MMC (GAUGE2D),
•ISO Tolerance input, Off-line programming, Operations on planar &
special curves (OPER2D)

130. Metrology
Metrology
Software
•Gauge inspection, Feature oriented measurement
(FEATRE),
•calculation of correction parameter for Gleason Phoenix
(BVPHNX),
•Measurement of Hob cutters (GDHOB),
Measurement of Gear shaper, Measurement of Gear
shaver, Palletized measurement. Measurement of
cylindrical and conical threads.

131. Metrology
Metrology
Basic Principle of Working on CMM
First clamp the job firmly on m/c bed in such a way that probe should
be accessible to all the geometry of the elements to be measured.
Align the job such that the min. two coordinate can be locked.
Make all the three reference co-ordinate (X,Y,Z) zero.
Measure all the elements & calculate various elements.
Save the program.
While checking repeat job just check the dimensions up to alignment
& run the program.

132. Metrology
Metrology
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