This document discusses metrology and inspection. It defines key terms like tolerance, fits, and fundamental deviation. It explains hole basis and shaft basis systems for dimensioning and tolerancing. It also describes various measurement tools and gauges used in inspection like micrometers, dial indicators, slip gauges, and interferometers. Measurement of linear, angular and surface features are discussed along with different types of fits and their tolerance calculations.

14. METROLOGY & INSPECTION
- BY GAURAV BABU

15. ❖Metrology :-
• Metrology is the science of measurement.
• It is the science behind quality assurance.
➢Important terminologies
1) Normal size –
• Size of a part specified in drawing
• Used for general identification.
2) Basic size –
• It is a size of part on which all limits of variation are provided.
Metrology & Inspection

16. 3) Actual size :–
• Size of part of a part measured by any specified measuring instrument.
4) Tolerance :-
• Difference b/w upper limit & lower
• limit Tolerance = Upper limit – lower limit
oImp Note: -
• Tolerance can’t be positive & negative.
➢Fundamental Deviation: -
• Deviation either upper or lower deviation which is nearest one to zero line.
oImp Note: -
• Fundamental deviation always represents with sign.

17. ❖Fits: -
The relationship b/w two mating parts that are to be assembled (that is hole &
shaft) with respect to the difference in their dimensions before assembly is
called fit.
In other words, it represents the degree of tightness & looseness b/w two
mating parts.

18. oTypes of fits: -
1) Clearance fit :-
• (LL)hole ≥ (UL)shaft
oImp Note
• Tolerance zone can never meet.
• Hole tolerance zone will be above the shaft tolerance zone.
Ex: - Slide fit, Easy slide fit, Running fit, slack running fit, loose, running fit
Minimum clearance = (LL)hole – (UL)shaft
Maximum clearance = (UL)hole – (LL)shaft

19. 2) Interference fit
• (LL)shaft ≥ (UL)hole
• Shaft tolerance zone will be above the hole tolerance zone.
➢Imp Note :-
• To interference fit, key is not required.
Minimum I = (LL)hole – (UL)shaft
Maximum I = (UL)hole – (LL)shaft

20. 3) Transition fit: -
Ex: - Push or snug fit and wringing fit
➢Important note :-
▪ key is required in transition fit.

21. ❖Allowance: -
Prescribed difference b/w the dimensions of two mating parts (hole & shaft)
In case of clearance fit
In case of interference fit
Allowance = (LL)hole – (UL)shaft
Allowance = minimum clearance
Allowance = maximum interference

22. ❖Hole basis system: -
• Hole is kept as a constant for different sizes of shaft.
• H represents the dimension of hole whose lower deviation is zero.
• For hole base system
• Lower deviation = Fundamental deviation = 0
• Shaft subjected to external machining
• suitable for mass production

23. ❖Shaft base system
• Shaft is kept as a constant for different sizes of hole.
• H represent the dimension of shaft whose upper deviation is zero.
• For shaft base system
• Upper deviation = fundamental deviation= 0
• Hole subjected to internal machining.
• Machining time will be more.

24. Hole-shaft Assembly Designation
Basic size
Hole tolerance zone
(FD of Hole)
Shaft tolerance zone
(FD of shaft)
H8 F7
# IT for Hole #IT for Shaft

25. ❖Fundamental Deviations & tolerances: -
ISO – International organization for standardization
According to IS – 919
25 grades of Fundamental Deviation
But ISO specified
28 grades of FD for both holes & shaft
oFor hole –
A, B, C, CD, D, E, EF, F, FG, G, H, J, JS, K, M, N, P, R, S, T, U, U, V, X, Y, X, ZA, ZB,
ZC.
oFor shaft –
a, b, c, cd, d, e, ef, f, fg, g, h, f, js, k, m, n, p, r, s, t, u, v, x, y, z, za, zb, zc.

26. ❖Imp Note –
J, JS, K, M, N - Transition fit
➢Tolerance calculation: -
Where,
K = const, depends on IT
Where,
i = 0.45 ×
3
D + 0.001 D
T = ki
D = D1D2 mm

27. ❖Imp Note –
for the dia calculation
D1 (mm) D2 (mm)
- 3
3 6
6 10
10 18
18 30
30 50
50 80
180 120
180 250
250 315
315 400
400 500

28. ❖Imp Note –
specifications for # IT of hole and shaft IT5
7i
IT9
40i
IT13
250i
IT6
10i
IT10
64i
IT14
400i
IT7
10i
IT11
100i
IT15
640i
IT8
25i
IT12
160i
IT16
1000i

29. ➢Plating on hole & shaft: -
Plating of hole, D ∝
1
T
(DAP)min = x – 2Tmax
(DAP)man = x – 2Tmin

30. Plating of shaft, D ∝ T
➢Gauge design →
• Limit gauging – Use of gauges for checking the limits of component.
(DAP)min = x + 2Tmax
(DAP)max = x +2Tmin

31. Limit gauge: -
• Inspection tool
• Used to check or inspect the limits of
a feature or component without measuring
actual size.
• Limit gauge are scale – less tools.
Type of gauges: -
1) Plug gauges –
• Used for checking the limits of hole.
Upper limit – No – Go plug
Lower limit – Go plug

32. 2) Ring or snap (or) gap gauge–
• Used for checking the limit of shaft.
Upper limit – Go – ring
Lower limit – No – Go ring
Gauge materials have: -
• High wear resistance
• Low co-efficient of thermal expansion
• Good machineability
• High corrosion resistance

33. Gauge Materials: -
• Mild steel
• High carbon steel
• Invar (36% Ni – Iron)
• Elinvar (42 % Ni + Iron)
(almost zero coeff. of thermal expansion)
• Glass – (in ordinance factories)

34. Measurement: -
1) Linear measurement
2) Angular measurement
3) Surface measurement
Linear measurement
1) Verner caliper
Least count =
Value of one main scale division
Total no of vernier scale division
Least count = 0.02 mm
Inspection & measurement of line/surfaces

35. 2) Micrometer: -
• Least count = 0.01 mm
• Least count =
𝑃𝑖𝑡𝑐ℎ
𝑁𝑜 𝑜𝑓 𝑑𝑖𝑣𝑖𝑠𝑖𝑜𝑛 𝑜𝑛 𝑐𝑖𝑟𝑐𝑢𝑙𝑎𝑟 𝑠𝑐𝑎𝑙𝑒
Dimension = main scale reading + circular scale reading × Lc

36. 3) Dial Indicator: -
• Least count = 0.1 mm
• It is a comparator, not a measuring device.
• It is very sensible
• Used for measuring roughness or flatness of surface
• Use for machine spindle setting

37. Application: -
• Checking dimension
• Centering work piece to machine tool spindle.
• Offset lathe tail stocks
• Aligning a vice on milling machine.

38. 4) Slip gauges or gauge stocks -
• Small blocks made up of allay steel.
• Used in the shop floor as length standards.
• Not to be used for regular & continuous measure.

39. 5) Filler gauge: -
• Used for measuring spark plug gap.
• Used for check the gap or clearance.
sidebar
Slip
gauge

40. Angular measurement: -
1) Bevel protector
2) Sine bar:
• Made with very high precision
Sin θ =
AB
AC
=
h
L
⇒ θ = sin-1 h
L
• Can not be used for conveniently measuring angle more than 45o
• Misalignment of work piece with sine bar may sometimes introduce considerable
errors.
sin θ =
h ± ∆h
L
sidebar
Slip
gauge

41. Interference principle: -
• Interferometer works on the interference principle.
Case – 1 Constructive inference: -
• Brighter fringe
• Crest + crest
(or)
Trough + trough
Case – 2 destructive interference: -
• Net amplitude = 0
• Loss in Amplitude
• Dark fringe
Interferometry

42. Imp Note: -
• Constructive interference → Amplitude ↑
• Descriptive interference → Amplitude ↓
• In interferometry uses light wave interference pattern by using optical flat
Experimental setup: -
Where,
∆H → difference in height of gauges (cm)
h → no of fringes/cm
𝜆 → wave length monochromatic
L → separation of edge. (cm)
Monochromatic light
∆H
Slip gauge
∆ℎ =
ℎ𝜆𝑙
2