Computer Aided Engineering Drawing 20ME12P DTE Karnataka

Vidya Vikas Education Trust ®
Viday Vikas Polytechnic College
Department of Mechanical (General)
Mr. THANMAY J S Be, M-Tech, H.O.D Mechanical (General), Vidya Vikas Polytechnic College, Mysore Page 1
Computer Aided Engineering Drawing (20ME12P)
Unit 1-Part 01
1. a) Illustrate the elements of dimensioning with the help of a sketch.
Elements of Dimensioning:
For any drawing to be workable, it is necessary that all the needful dimensions should be written
on it, so that all information could be used properly. For this purpose, the following elements are
written down.
1. Dimension Line.
2. Extension Line.
3. Center Line.
4. Leader Line.
5. Arrow Head.
6. Numbers.
1. Dimension Line:
A Dimension Line is drawn for a given dimension of an object. This line should be at a distance
from 10 mm to 15 mm from the object line. For writing a dimension, this line is broken from the
middle, and the dimension is written in the middle space. Alternatively, the dimension is written
on it after its completion. 2H or 4H pencil is used for this purpose.
2. Extension Line:
Such lines which are drawn extending from the ends of a part of a drawing so that the dimension
can be written in between them are called extension lines. 2H or 4H pencil is used for this
purpose. There should be a distance of 1 mm between them and the object line.
3. Center Line:
Such a line is used to represent the center of a cylindrical part of a drawing. For example, a hole
shaft, etc. This should be extended up to 1 mm distance from the object line.
4. Leader Line:
Any note or specification is written on an object with the help of this line. This is drawn with 2H
or 4H Pencil. It consists of a circle and a leader.
5. Arrow Head:
This is used at the ends of a dimension and the end of a leader. The length of the arrow-head
used in engineering drawing 3 mm.
6. Numbers:
After the completion of any geometric shape of an object, the writing of its size is desired.
Numbers are used for this purpose. The height of the number is kept 3 mm.

Figure: Example for Elements of Dimensioning
1. b) Illustrate the dimensioning of given common features: diameter, radius, chord,
Arc and angle.
i) Dimensioning diameters
Circular features like cylindrical parts like
shafts, pipes, rods or any other round shape are
always dimensioned by indicating their
diameter. The diameter is indicated by the
symbol ∅. The diameters on the circular
objects may be indicated in any one of the
following ways as shown in fig.
Note: All Dimensions are in millimeters.
ii) Dimensioning Radius
The curved, fillets and round figures are shown
in drawings by arcs or circles. The
dimensioning is done by giving radii. The
measured radius is indicated by letter R. The
dimension line is drawn radial with the
arrowhead touching the arc.

iii) Dimensioning Arcs
When dimensioning the length of an arc the
dimension figure identified by symbol being
written above the dimension.
iv) Dimensioning Chords
It is a linear distance between any two points
of an arc. And it is dimensioned as shown in
the figure.
v) Dimensioning Angles
The angles are dimensioned in the same
manner as that of linear dimensions.
2. a) Mention the uses of the following drawing instruments.
i) T-square
T square is used to draw horizontal and vertical lines on
drawing sheet. It made of wood or plastic and in T shape. The
vertical part of T is called as blade and horizontal part of T is
called as head. The edge of head is uniform level and attached
to the edge of the board. The working edge is used to draw
lines anywhere on the sheet by moving the instrument top to
bottom. Note: Free Hand Sketch
ii) Set square
Set squares are used to draw lines with an angle between
them. In most of the structures, 30, 45, 60 and 90-degree lines
are most common. Generally, set squares are of two types.
One is 45 degree set square and another one is called as 30 –
60 degree set square. Note: Free Hand Sketch

iii) Bow compass
A small pair of compasses one leg of which carries a pencil,
pen, or point, its legs being connected by a bow-shaped spring
instead of by a joint. Compass is used to draw an arc or circle
with known dimensions on engineering drawing. The needle
tip is placed at the respected point and pencil tip is adjusted to
the height at least 1mm just above the tip of the needle. The
gap is nothing but the paper thickness. Note: Free Hand
Sketch
iv) Clinograph
Clinograph is an instrument used to draw parallel lines to the
inclined lines. It contains one adjustable wing or strip which
can be adjusted to required angle. So, it can be termed as
adjustable set square. Note: Free Hand Sketch
v) Mini drafter or Drafting Machine
Mini drafter is an instrument which can be used for multiple
functions in drawing. It contains two arms which are
adjustable to required angle and at the end of the lower arm a
scale set is attached. The scale set contains two scales
connected perpendicular to each which cannot be separated.
This instrument is fixed to the drawing board at one edge
with the help of screw provided for the drafter. Mini drafter
is used for drawing horizontal lines, vertical lines, inclined
lines, angles, parallel lines, perpendicular lines etc. Note:
Free Hand Sketch
2. b) Mention the uses of the following drawing instruments.
i) French curves
French curves are made of plastic and they are in
irregular shapes. Sometimes the drawing requires
irregular curves or shapes or arcs which cannot be
drawn using compass. Generally French curves are
more suitable for small curves and for long curves
splines are used. Note: Free Hand Sketch

ii) Protractor
Protractor is used to draw and measure the angles of
lines in the drawing. It is transparent and made of
plastic. It is in the shape of semi-circle, and the edge
of semi-circle part consists reading with one-degree
accuracy. The bottom line joins the 0o
to the 180o
.
The center of this bottom line is marked as “O” or
“C” from which the angles are measured. Note: Free
Hand Sketch
iii)Clips
The clips are used to hold the drawing sheet on the
drawing board properly. Generally, 4 clips are used
for any drawing sheet. Note: Free Hand Sketch
iv)Erasing Shield
An eraser shield is a thin sheet of stainless steel or
plastic with slots and holes of different shapes. They
are designed to allow erasers to be used through them
to erase lines and text without removing lines close
by which do not need to be (or should not be) erased.
They are about the size of a business card but the
shape of the slots depends on the manufacturer. Some
stainless eraser shields are made of see-through steel
mesh so that the sections to be erased are easy to see.
Note: Free Hand Sketch
vi) Drafting machine-Same as Mini Drafter

3. Define RF. Mention the types of scales based on RF.
Representative fraction is the ratio of the length of the object represented on drawing to the
actual length of the object represented.
There are three types of scales depending upon the proportion it indicates as
1. Reducing scale: When the dimensions on the drawing are smaller than the actual dimensions
of the object. It is represented by the scale and R.F as
Scale: - 1cm=100cm or 1:100 and by R.F=1/100 (less than one)
2. Full scale: Sometimes the actual dimensions of the object will be adopted on the drawing then
in that case it is represented by the scale and RF as
Scale: - 1cm = 1cm or 1:1 and by R.F=1/1 (equal to one).
3. Enlarging scale: In some cases when the objects are very small like inside parts of a wrist
watch, the dimensions adopted on the drawing will be bigger than the actual dimensions of the
objects then in that case it is represented by scale and RF as
Scale: - 10cm=1cm or 10:1 and by R.F= 10/1 (greater than one)
Note: The scale or R.F of a drawing is given usually below the drawing. If the scale adopted is
common for all drawings on that particular sheet, then it is given commonly for all figures under
the title of sheet.

4. Draw the conventional representation of lines
A; Continuous Thick Line: Surroundings and sides of the matters (Outlines of the Edges), End
of the Screws,
B; Continuous Thin line: Measure lines, Backside section lines, Implied axis lines, to state the
code of the planes, at diagonal lines which are used to state plane surface, Intersection, Leader,
Hatching.
C; Free Hand Line: Limits of partial and interrupted views and sections
D; Continuous Thin Zigzag Line: It is used when free hand lines are drawn by tools
E; Dashed Thick Lines with Dots: to state the special places / surfaces this will process
additionally like to coat, to harden etc.
F; Dashed Thin Lines: Invisible/Hidden Lines represents an invisible edges on the on an
objects.
G; Chain thin: Axis lines of symmetrical drawings, In front of section planes.
K; Chain Thin with Thick Ends: Cutting Plane, to draw the trace at section planes,

5 Draw six horizontal parallel lines of 50 mm long with 10 mm intervals (Fig 1).
6 Draw six vertical parallel lines of 50 mm length with 10 mm intervals (Fig 2)
7 Draw 45° inclined lines (Fig 3). A to B 90 mm and B to C 6o mm Note each division 10
mm

8 Draw the given types of lines using 0.5 range thickness of line according to the
specification (Fig 4).
Note: These types of Line are Hatching lines (B5): Hatching lines are the lines which are
Parallel or inclined. The minimum space between these lines should be more than twice the
thickness of the heaviest line in the drawing. It is recommended that these spacing should never
be less than 0.5 cm that is 5 mm.

9 Draw the following Exercises in A4 sheet or in your Sketch book according to the
dimensions (Fig 5).

10 Draw the pattern drawing given Figure 1, 2, 3
Note SQ stands for Square of size

11 a) Illustrate the elements of dimensioning with the help of a sketch.
b) Illustrate the dimensioning of given common features: diameter, radius, chord,
Arc and angle.
Note: 11 a and b are repeated questions do not rewrite these two questions.
DIMENSIONING SYSTEM AND TYPES
Note: this is a theory part not required to be written in sketch book
System in Dimensioning
Following are the two systems of writing dimension.
1. Unidirectional Method.
2. Aligned Method.
1. Unidirectional Method:
This method is mostly used in
dimensioning. In this method, the whole
dimension is written in the same
direction in the whole drawing. This
direction is generally vertical.
2. Aligned Method:
In this method of dimensioning, it is
written in two directions in the whole
drawing.
It is written upward and at the right side
and is read from the bottom and right
side of a drawing.
Its advantage is this that the dimensions
can be written in the horizontal direction
which is very easy to write.

Types of Dimensioning
1. Chain dimensioning: It is used where the possible accumulation of tolerances does not
infringe (effect) on the functional requirement of the component. Dimensioning from a
common feature is used where a number of dimensions of the same direction relate to a
common origin.
2. Parallel dimensioning: Dimensions of features are taken from one datum/common
origin and are shown parallel to other and placed, so that the dimensional values can
easily be added.

3. Superimposed running dimensioning (Progressive dimensioning): It is a simplified
dimensioning also cumulative error is controlled. It starts from one origin with arrow
heads in one direction only. This may be used where there are space limitations and
where no legibility problems would occur. The origin indication is placed appropriately
and the opposite ends of each dimension line shall be terminated only with an arrow
head. It may be advantageous to use superimposed running dimensions in two directions.
4. Combined dimensioning: Dimensions are given in chain dimensioning and parallel
dimensioning. Common feature is combined.

Principles of Dimensioning
Note: this is a theory part not required to be written in sketch book
After completing a drawing, it is necessary that its measurements and notes should be written in
such a way that they can be read easily. Follow are the Principles that have been devised for this
purpose.
1. The dimensions should be given on such view which illustrates the true shape and size of an
object.
2. As far as possible the dimensions should be given outside a view but can be given inside as
well if unavoidable.
3. All the dimensions are given in group form. Scattering of these is not correct.
4. The dimensions should be intelligibly written.
5. All the dimensions should be written parallel to the object line and the numbers should be
written such that they could be read easily.
6. The dimensions should not be repeated unless necessary.
7. The unnecessary dimensions should be avoided.
8. The extension and dimension lines should not intersect in any case.
9. While giving dimension after completing a drawing, it should be kept in mind that no unit
should be written with any number.
10. The numbers should be clear, legible, and intelligible.
11. The circle, arcs, and wholes should be compatible with their radius of diameter.
12. If dimensions are needed to be given in concentric circles, then try to make them on the front
view and then write their dimensions.
13. The Leader Line should be used for writing dimensions of the circles which should illustrate
their diameters.
14. Refrain from ambiguous and complicated dimensions.

12 Copy the sketch to 1:1 scale and dimension it using Aligned system.
Note: фaa, фbb and фcc are the dimensions to be measured from the figure manually using
scale
13 Copy the sketch to 1:1 scale and dimension it using unidirectional system with Parallel
Dimensioning method.
Note: фaa, фbb, фcc, фdd, фee and фff are the dimensions to be measured from the figure
manually using scale
14 Copy the sketch to 1:1 scale and dimension it using Aligned system with Chain
dimensioning method.
Note: aa, bb, cc, dd, ee, ff, gg, hh, ii, jj and фkk are the dimensions to be measured from the
figure manually using scale

15 Copy the sketch to 1:1 scale and dimension it using Aligned system with Parallel
Note: aa, bb, cc, dd, ee, ff, gg, hh, ii and jj are the dimensions to be measured from the figure
16 Copy the sketch to 1:1 scale and dimension it using unidirectional system with Chain
dimensioning method
Note: aa, bb, cc, dd, ee, ff, gg, hh, ii, jj, kk, ll and mm are the dimensions to be measured from
the figure manually using scale

17 Copy the sketch to 1:1 scale and dimension it using unidirectional system with Parallel
Note: aa, bb, cc, dd, ee, ff, gg, hh, ii and jj are the dimensions to be measured from the figure
15 Copy the sketch as shown in figure below dimension it in a Chain and parallel
dimensioning

Computer Aided Engineering Drawing 20ME12P DTE Karnataka

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