Machine Element Drawing

1. MACHINE DRAWING

2. Principle of Drawing
Toprovide the correct information about drawings to all concerned
people, the drawing must be prepared,following certain standard
practices, as recommended by Bureau of Indian Standards (BIS).
• Sheet Size- For a reference size A0 having
a surface area of 1
X = 841 mm and Y = 1189 mm.

3. Drawing Sheet Size
Assembly Drawing
Working Drawing

4. • Title Block –
(i) Title of the drawing
(ii) Sheet number
(iii) Scale
(iv) Symbol, denoting the method of projection
(v) Name of the firm / institute
(vi) Initials of staff drawn, checked and approved.

6. • Borders & Frames –
Minimum 20 mm for size A0 & A1.
Minimum 10 mm for size A2, A3,A4.
• Centering Marks
• Metric reference
graduation
• Grid reference
system
• Trimming mark

7. Types of lines and their applications

8. Types of lines and their applications

9. PROJECTION SYSTEMS

10. PROJECTION SYSTEMS
1. First angle system
2. Third angle system
First Quadrant
Third
Quadrant
- European country
- ISO standard
- Canada, USA,
Japan, Thailand

11. ORTHOGRAPHIC PROJECTION
1st angle system 3rd angle system

12. ORTHOGRAPHIC VIEWS
1st angle system 3rd angle system
Folding
line
Folding
line
Folding
line
Folding
line

13. ORTHOGRAPHIC VIEWS
1st angle system 3rd angle system
Front View
Front View
Right Side View
Right Side View
Top View
Top View

14. First angle system Third angle system
PROJECTION SYMBOLS

15. Scales
• The various types of scales used in machine drawing are
1. Full scale 1:1
2. Reduced scale 1:X
3. Enlarged scale X:1
The standard scales are given in Table

16. Dimensioning
1. As far as possible, dimensions should be placed outsidethe
view.
2. Should be taken from visible outlines, not from hiddenlines.
3. Dimensioning to a centre line should be avoided except
when the centre line passes through the centre of ahole.
4. Each feature should be dimensioned only once in a drawing.
5. Placed on the view or section that relates most clearly tothe
corresponding features.
6. Each drawing should use the same unit for alldimensions,
but without showing unit symbol.
7. Minimum dimensions should be placed to define awhole
part.
8. No features of a part should be defined by more thanone
dimension in any one direction.

17. Elements of Dimensioning
1. Dimension line — It is a thin continuous line terminated by arrowheads
touching the outlines, extension lines or centre lines away from outline by 8 mm.
2. Extension line (Projection line) — It is a thin line drawn outside and along the
outline. There should be a gap of about 1 mm between the extension line and the
outline.
3. Leader line —One end of the leader terminates either in an arrowhead or a dot.
The arrowhead touches the outline, while the dot is placed within the outline of
the object. The other end of the leader is terminated at a horizontal line
4. Arrowhead — An arrowhead is placed at each end of a dimension line. Its pointed
end touches an outline, an extension line or a centre line. The length of
arrowhead should be about three times its maximum width. The triangle of the
arrow should be completely filled in.

18. Methods of indicating Dimensions
1. Aligned system, and
2. Unidirectional system.
1. Aligned system — In the aligned system, the dimensions are
placed above the dimension lines and may be read either from
the bottom or from the right side of the drawing
2. Unidirectional system — In the unidirectional system, all
dimensions are placed with respect to the bottom of the
drawing, irrespective of the disposition of the dimension line.
In the system, the dimension lines are broken to insert their
dimensions . This system is preferred for big drawings specially
when it is not convenient to read the dimension from the right
side or any other direction.

19. Symbols & Joints
Welding Symbols

24. Limits , Fits and Tolerance
• The system in which a variation in dimensions is acceptedis
called the limit system.
• The allowable deviations are called tolerances.
• The relationships between the mating parts are calledfits.

25. Tolerance: The permissible variation of a size is called tolerance. It is the
difference between the maximum and minimum permissible limits of the given
size.
Limits: The two extreme permissible sizes between which the actual size is
contained are called limits. The maximum size is called the upper limit and the
minimum size is called the lower limit.
Deviation: It is the algebraic difference between a size (actual, maximum, etc.)
and the corresponding basic size.
Actual Deviation: It is the algebraic difference between the actual size and the
corresponding basic size.
Upper Deviation: It is the algebraic difference between the maximum limit of the
size and the corresponding basic size.
Lower Deviation: It is the algebraic difference between the minimum limit of the
size and the corresponding basic size.

26. HOLE BASIS SYSTEM, SHAFT BASIS SYSTEM
In working out limit dimensions for the three classes of fits; two systems are in use, viz., the hole
basis system and shaft basis system
HOLE BASIS SYSTEM: In this system, the size of the shaft is obtained by subtracting the allowance
from the basic size of the hole.
In this system, the lower deviation of the hole is zero. The letter symbol for this situation is ‘H’.
SHAFT BASIS SYSTEM: In this system, the size of the hole is obtained by adding the allowance to
the basic size of the Shaft. plied to each part.
In this system, the upper deviation of the shaft is zero. The letter symbol for this situation is ‘h’.

27. Method of placing limit dimensions
Method 1

28. Method 2

29. Method 3

30. Types of Fits
1. Clearance Fit –
It is a fit that gives a clearance between the two mating
parts.

31. Types of Fits
2. Transition Fit –
This fit may result in either an interference or aclearance,
depending upon the actual values of the tolerance of
individual parts.

32. Types of Fits
3. Interference Fit -
If the difference between the hole and shaft sizes isnegative
before assembly; an interference fit is obtained.

33. Schematic Representation of Fits

34. Surface finish
The geometrical characteristics of a surface include,
1. Macro-deviations,
2. Surface waviness, and
3. Micro-irregularities.
The surface roughness is evaluated by the height, Rt and mean roughness
index Ra of the micro-irregularities.

35. Surface Roughness Symbols

37. Machine Symbols: The basic symbol consists of two legs of unequal length,
inclined at approximately 60° to the line, representing the surface considered. This
symbol may be used where it is necessary to indicate that the surface is machined,
without indicating the grade of roughness or the process to be used
A. Basic symbol. B. Material Removal is Not Allowed
C. Removal Of Material Is Allowed
D. Special surface characteristics

40. Indication of Surface Roughness

41. Indication of Surface Roughness

43. Classification of Drawing
• Machine Drawing-
- Pertaining tomachine
parts or components.
- presented througha
number of
orthographicviews.
- Size & shape of
component is fully
understood.

44. • Production Drawing –
- Referred as working drawing.
- Should furnish all dimensions, limits & special finishingprocesses
such as heat treatment, honing, lapping, surface finish,etc.
- Title should also mention the material used for the product,number
of parts required.

45. • Part Drawing-
- Detailed drawing of a
component to facilitateits
manufacture.
- Follows principles of
orthographicprojection
• Assembly Drawing-
- A drawing that shows the
various parts of a machine
in their correct working
locations.