engg drawing
TRANSCRIPT
Introduction
1
What is Engineering Graphics
Language used for accurate description of physical objects
Definition of Engineering Graphics: A graphic representation of physical objects
and relationships.
The graphic representation is accomplished by describing both shape and size
Objective of Engineering Graphics
To be able to express ourselves clearly and be able to understand what is written by
others
Two fundamental methods used in Engineering Graphics
• Freehand
• With instruments
2
Main Constituents of Engineering Graphics
• Shape is described by means of projection – a process of causing an image to be
formed by lines (projectors) taken in a particular direction from an object to a
particular plane
• Two main types of projections are used
• Orthographic
Separate views are made and properly arranged to show all the details
of the 3D object on mutually perpendicular planes. Each projection
represents two dimensions of the object
• Pictorial
The 3D object is represented on a plane by one view only
Shape Description
Size Description
• Size is shown by ‘dimensions’ which show linear distances, diameters, radii, angles
• Need to show only those dimensions which convey the information in the best
possible way
3
Orthographic Projection
Projectors are parallel to each other and perpendicular to the plane of projection
Two reference or principal
planes of projection
V.P. – vertical (frontal) plane
H.P. – horizontal plane
Projection on V.P. – front view
or elevation
Projection on H.P. – top view
or plan
Intersection of the V.P. and the
H.P. is called the reference line
and is denoted by xy
Ref: Engineering Drawing by N. D. Bhatt et. al
4
Methods of Orthographic Projects
Only the 1st and the 3rd quadrants are opened out
Basic Four Quadrants
• First Angle Projection
• Third Angle Projection
Ref: Engineering Drawing by N. D. Bhatt et. al
5
First Angle Projection
• Object is assumed to be situated
in the first quadrant
• Object lies between the observer
and the plane of projection
• The top view comes below the
front view
• Each projection shows the view
of the surface which is remote
from the plane on which it is
projected
• The view of the of the object as
observed from the left-side is
drawn to the right side of the
front view and vice versa
Recommended by the Bureau of Indian Standards (B.I.S)Ref: Engineering Drawing by N. D. Bhatt et. al
6
Third Angle Projection
• Object is assumed to be situated
in the third quadrant
• Plane of projection lies between
the observer and the object
• The top view comes above the
front view
• Each projection shows the view
of the surface which is nearest
to the plane on which it is
projected
• The view of the of the object as
observed from a particular side is
drawn to the same side of the
front view
Ref: Engineering Drawing by N. D. Bhatt et. al
7
Symbols for Method of Projections
On any drawing it essential to indicate the method of projection adopted
Ref: Engineering Drawing by N. D. Bhatt et. al
8
Six Views of an Object
• In some cases two views (front and top) may not be sufficient to describe the object
completely
• Need to use additional views (right hand side view, left hand side view, bottom view
and back view)
• Method: Assume that the object is enclosed in a square box and carry out the
projections on the faces of the box using either first angle or third angle method
Ref: Engineering Drawing by N. D. Bhatt et. al
9
Dimensioning
• Size is shown by ‘dimensions’ which show linear distances, diameters, radii, angles
• Need to show only those dimensions which convey the information in the best
possible way
Placing of Dimensions
Aligned System Unidirectional System
Ref: Engineering Drawing by N. D. Bhatt et. al
10
Rules for Dimensioning
• Dimensioning should be done completely
• Each dimension should be given only once
• Dimensions should be placed outside the views
• Mutual crossing of the dimension lines should be avoided
• Dimensioning of hidden lines should be avoided
• Dimension lines should not cross any other lines of the drawing
• An outline or a center line should not be used as a dimension line
• A zero is should always precede the decimal when the dimension is less than
one, i.e. write 0.5 instead of .5.
11
Dimensioning of Some Common Features
Dimensioning of Circles Dimensioning of Radii
• Dimension figure should be preceded
by ø• Holes should be dimensioned in the view
in which they appear as circles
• Hole center should be located by center
lines
• Dimension figure should be preceded
by R• Arcs of circles should be dimensioned
by respective radii
• Dimension line of the radius should
pass through the center of the arc
Ref: Engineering Drawing by N. D. Bhatt et. al
12
Types of Lines
• Outline/Object lines (thick)
• Hidden lines (thin)(dash space dash space ….)
• Dimension lines (thin)
• Leader lines (thin)
• Center lines (thin)(long dash space short dash space long dash ....)
• Extension lines (thin)
• Section lines (thin)
(inclined at 450)
• Break lines (thick)
• Cutting plane lines (thick)
Each line has a definite meaningRef: Engineering Drawing by N. D. Bhatt et. al
13
Precedence of Lines
Coincident lines may exist in the same view. In such a case, use the following
order to establish the precedence
• Visible object lines
• Hidden lines
• Center line or cutting plane lines
• Break lines
• Dimension and extension lines
• Crosshatch/section line
14
Problem 1
Draw the front view, top view and the left hand side view of the object
Ref: Engineering Drawing by N. D. Bhatt et. al
Problem 1 - Solution
Ref: Engineering Drawing by N. D. Bhatt et. al 15
Important to indicate the
projection method used. Has
to be there in all your drawings
16
Problem 2
Draw the front view, top view and the left hand side view of the object
Ref: Engineering Drawing by N. D. Bhatt et. al
17
Problem 2 - Solution
Ref: Engineering Drawing by N. D. Bhatt et. al
Important to indicate the
projection method used. Has
to be there in all your drawings