1. LIMITS, FITS & CALCULATIONS

2. Fig. 1.1 Graphical Illustration of Fits and Tolerances
ILLUSTRATION OF BASIC SIZE DEVIATIONS,
LIMITS AND TOLERANCES

3. LIMITS
Actual machine size - between the maximum
and minimum limits
MAXIMUM LIMIT
Maximum permissible machine size corresponding to basic
size.
Fig. 1.1, Ø 30 mm is = Ø 30 + 0.035 = Ø 30. 035 mm.
Basic size Maximum limit
MINIMUM LIMIT
Minimum allowable machine size corresponding to basic
size.
In Fig. 1.1, Ø 30 mm is = Ø 30 - 0.215 = Ø 29. 785 mm.
Basic size Minimum limit

4. TOLERANCE
The difference between the maximum and minimum limits
of a size is tolerance.
In Fig. 1.1 the tolerance is = Ø 30.035 - Ø 29.785 = 0.25m.
Max. limit Min. limit Tolerance
DEVIATION
(Actual, or maximum, or minimum) – (Basic size).
UPPER DEVIATION - (Maximum limit) – (Basic size)
In Fig.1.1, the upper deviation is = Ø 30.035 - Ø 30
= 0.035 mm.

5. LOWER DEVIATION - (Minimum limit) – (Basic size)
In Fig. 1.1, the lower deviation is = Ø 29.785 - Ø 30
= - 0.215 mm.
ACTUAL DEVIATION - (Actual measured size) – (Basic size)
In Fig. 1.1, the actual deviation = Ø 29.925 - Ø 30
= - 0.075 mm.
ZERO LINE
• A straight line drawn for the basic size is called zero line.
• Upper and lower deviation are referred to zero line.
• Zero line is drawn horizontally.
• Above zero line - positive deviations.
• Below zero line - negative deviations.

6. TOLERANCE ZONE
The zone bounded by the upper and lower limits of the
basic size.
In Fig. 1.1, tolerance zone is shown by hatched line.
FITS
• The relationship between the mating surfaces of
the parts,because of the difference in dimensions
is
called fit.
• Thus fit has a characteristic effect on the
performance of mating parts.
• Example: width of the slot & the thickness of the
key.

7. CLEARANCE
 (Hole dimension) – (Dimension of shaft that fit to it).
Maximum - hole size is maximum and the shaft size is
minimum.
Minimum - shaft size is maximum and the hole size is
minimum.
CLASSIFICATION OF FITS
Clearance fit
Interference fit
Transition fit

8. A
B
Fig. 1.2 Clearance Fit
Min hole – Max Shaft = + ve – clearance fit.
Fit with positive clearance between the hole and the shaft.
CLEARANCE FIT

9. INTERFERENCE FIT
Fit with negative clearance between the hole and the shaft.
Fig. 1.3 Interference Fit
Max hole – Min Shaft = - ve – interferance fit

10. TRANSITION FIT
Fit established when the dimensions of the hole are
such that there exists either a positive clearance or a
negative clearance when the shaft is fitted into the hole.
B

11. Fig 1.4 Transition Fit

12. TRANSITION FITS AND INTERFERENCE FITS
Combination of
Hole and Shaft
Quality of Fit Typical uses
H6 j5 fine
Clearance
transition
Very small clearance is obtained - used for fits where a
slight interference is permissible - coupling spigots and
recesses, gear rings clamped to steel hubs.
H7 j6 normal
H8 j7 coarse
H6 k5 fine
True
transition
Fits averaging no clearance where slight interference can be
tolerated , with the object of eliminating vibration - ball
bearings races of light duty.
H7 k6 normal
H8 k7 coarse
H6 m5 fine
Interference
transition
Fits averaging slight interference - used for ball bearing
races of medium duty.
H7 m6 normal
H8 m7 coarse
H6 p5 fine
Press fit
Light press fit for nonferrous parts which can be dismantled
when required-bearing bushes-press fit for steel, cast iron
or brass to steel assemblies- bush in a gear.H7 p6 normal
H6 r5 fine
Drive fit Medium drive fit for ferrous parts and light drive fit for
non-ferrous parts that can be dismantled.H7 r6 normal
H6 s5 fine
Drive fit
Permanent or semi permanent assemblies of steel and cast
iron with considerable gripping force- collars pressed on to
shafts, valve seatings etc. For light alloys this gives a press
fit.
H7 s6 normal
H6 u5 fine
Force or
shrink fit
High interference fit a thorough investigation into the
degree of grip and the stresses in the part must be made.H7 u6 normal

13. SYSTEMS OF FITS
HOLE BASIS SYSTEM: the hole is constant in
diameter and various types of fits are obtained by
suitably varying the limits of the shaft.
SHAFT BASIS SYSTEM: the shaft is constant in
diameter and various types of fits are obtained by
suitably varying the limits of the hole.

14. Fig. 1.5 Hole Basis System
Clearance Fit
B
Interference Fit
C
HOLE BASIS SYSTEM
Single hole, whose lower deviation is zero.
Minimum limit of the hole will be equal to its basic size.

15. Grades of
Holes
MANUFACTURING PROCESS USED
H5 Fine Boring, Fine Grinding, Honing
H6 Fine Boring, Honing, Hand Reaming
H7 Int. Grinding, Broaching, Reaming
H8 Boring, Machine Reaming
H9 Boring & Reaming
H10
Not for diameter fits; used for milled widths,
drilled holes
H11
Not used in fits; punching, coarse drilling drawn
recesses

16. HOLE BASIS SYSTEM - Design Example
Requirement
Hole basic size - 20 mm diameter.
Clearance of - 0.100 mm.
Hole tolerance - 0.025 mm.
Shaft tolerance - 0.050 mm.
Minimum limit of the hole is Ø 20 mm.
Maximum limit of the shaft = Lower limit of the hole –
Minimum clearance
= Ø 19.900 mm
Design

17. Minimum limit of the shaft = Maximum limit of the shaft –
Tolerance on the shaft.
= Ø 19. 850 mm.
Shaft
Max. limit = Ø 19.900 mm.
Min. limit = Ø 19. 850 mm.
Maximum limit of the hole = Maximum limit of the hole +
Tolerance on the hole.
= Ø 20. 025 mm.
Hole
Max. limit = Ø 20.025 m.
Min. limit = Ø 20. 000 mm.

18. Why the Hole Basis System is Preferred?
Holes are produced by drilling, boring, reaming,
broaching, etc.,
Shafts are either turned or ground.
Shaft basis system - Holes of different sizes are required,
(requires tools of different types and
sizes).
Hole basis system - Only one tool is required, to
produce the hole and the shaft can
be machined to any desired size.

19. SYSTEMS OF TOLERANCING
1. UNILATERAL SYSTEM
• Deviations are allowed in only one direction from the
basic size.
• The deviation in the other direction is zero.
• Hence, either the maximum limit or the minimum
limit will be equal to the basic size.
• Deviations are allowed in both the directions from
the basic size.
• The deviations are allowed in both the directions.
• One of the limits - above the basic size.
• Other limits - below the basic size.
2. BILATERAL SYSTEM

20. FUNDAMENTAL TOLERANCES OF GRADES

21. MACHINING SYMBOL

22. MACHINIG PROCESS AND THEIR Ra VALUES

23. ATTAINABLE SIZE TOLERANCE
Sl.
No.
Machining
Process
IT
Value
Tolerance value
(for a size of
20 mm)
1 Drilling IT12 0.21
2 Milling IT10 0.084
3 Turning/ Boring IT8 0.013
4 Grinding IT6 0.006
5 Lapping IT4 0.006
6 Broaching IT7 0.021
7 Shaping IT12 0.210
8 Reaming IT8 0.033
9 Hobbing IT7 0.021
10 Surface grinding IT4 0.006
11 Honing IT7 0.021

24. GEOMETRIC TOLERANCE

25. What machining process should be adopted to each
step of the following components. Also give step
drawing details ?
(a)

26. (b) (c)

27. REFERENCE
1. Gopalakrishna K R, “Machine Drawing”, Tenth
Edition, Bangalore, 1996.
2. Faculty of Mechanical Engineering, PSG College of
Technology, “Design Data Book”, Coimbatore, 1993.
3. ASME Y 14.5M- 1994, “Dimensioning and
Tolerancing”, ASME, New York, 1995.

28. THANK YOU