drawing presentation 2015 2016
TRANSCRIPT
MET 101. ENGINEERING DRAWING.
EEE 2015-2016
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CONTENTS
Section I
Introduction
Drawing Instruments
Lettering
Types of lines
Dimensioning
Scales2
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CONTENTSSection II: Plane geometry and surfaces
Definition and construction of angle, triangle, circles.
Construction of external and internal tangents: - circle and
arc tangents
Polygons: Construction of pentagon, hexagon, heptagon
and octagon
Conic section
Cycloid involutes, spirals andHelices
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CONTENTS
Section III: PROJECTIONOrthographic projection
Projection of point
Projection of strait lines
Auxiliary plane projection method
Projection of plan surfaces
Projection of solid
Sections of solid
Development of surface of a solid
Intersection of surfaces of solids
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ENGINEERING DRAWING
Drawing is the graphical language of engineers, which is built upon certain basic principles and standards.
A good drawing: Presentation of an object, of a part of it, and is the result of creative thought by engineer or technician.
Engineering drawing is a two dimensional representation of three-dimensional objects.
In general, it provides necessary information about the shape, size,surface quality, material, manufacturing process, etc., of the object.
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ENGINEERING DRAWING (cont.)
Engineering Drawing is not a subject to study but it is a
Graphical Language To equip students with basic skills
required in engineering drawings, electrical circuit
diagrams, and communication that all engineers must
know about to Read, Speak and Write it.
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ENGINEERING DRAWING STANDARDS
Drawing STANDARDS are sets of rules that govern
how technical drawings are represented.
Standards allow for the clear communication of technical
ideas.
Drawing standards are used so that drawing convey the
same meaning to everyone who read them.
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Classification of drawing
Artistic drawing (free hand or model drawing)
Representation of an object such as painting, cinema slide,
advertisement boards, etc by the artist by his imagination or
by keeping the object before him
Engineering drawing (Instrument drawing)
Representation engineering object such as buildings,
roads, machines, etc on paper is called Engineering
drawing.
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GEOMETRICAL DRAWING
Plane geometrical drawing:
The art of representation objects having two
dimensions
Solid geometrical drawing:
The art of representation of objects having three
dimensions
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Applications
Confer books
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DRAWING INSTRUMENTS AND MATERIALS
A draftsperson needs some basic tools to draw. These should include the following:
●A range of pencils ● Drawing board
● Ruler ● Instrument box (Compasses)
● Standard Set squares ● Dividers
● Rubber / Pencil eraser ● T-square
● Emery board or fine sandpaper ● Clips or tape
Protractor
French curves
Adhesive tape
Sharpener
Mini-Drafter
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Drawing Board
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Standard size of Drawing boards
DesignationSize (mm)
B0 1500 × 1000
B1 1000 × 700
B2 700 × 500
B3 500 × 350
B4 250 × 350
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T-square17
Drafting machine (or Drafter)
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Set Squares
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Set Squares
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Protractor
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Drawing Pencils
B=Black HB=Hard-
Black
F=Firm H=Hard
… 3B 2B B HB F H 2H 3H …
Softer Harder
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Lead-mine pens
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Ink pen
You will need a selection of pencils. A hard leaded pencil (6H) can be
used for light lines, a softer pencil (2H) for the outlines and an even softer pencil
(HB) for printing. (More than one pencil of each grade will save you from
frequent re-sharpening.)
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You will need at least two compasses: a
small spring bow compass for small
circles and one for larger circles.
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33Before you start any drawing you first decide how large the
drawings have to be.
The recommended scales in Engineering Drawing
are
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SCALE SPESFICATION
If all drawings are made to the same scale, the scale should be indicated in or
near the title block. Where it is necessary to use more than one scale on a
drawing, the main scale only should be shown in the title block and all the
other scales, adjacent to the item reference number of the part concerned or
near the drawings.
Exercise 1
Draw the simple key shown in Fig. 1 full size.
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FOLDING
Only format A4 is convenient for filling. Other
formats (larger in size) exceed the size of the file
and thus must be folded before filing.
Drawings which that do not need fastening are
fold in a logical way to give an A4 size.
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FOLDING (Cont.)
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FOLDING (Cont.)
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TITLE BLOCK
In every engineering drawing, a Title
Block is included at the bottom right-
hand corner.
The Title Blocks are locally
standardized but should be designed in
such a way that it can be easily
understood.
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TITLE BLOCK Cont.
Name of the Firm/School/College Name of the Object (Work piece) Number of the drawing (particularly useful for reference where more than one
drawing are concerned --- typically in assembly drawings) Format of the paper used (paper size) Scale used Dimensioning unit (usually millimeters --- mm) Symbol for the method of projection used Date when the drawing was finished Name of the draftsman (draughtsman) --- e.g. student name if it is a normal
class exercise Name of the person who checked the drawing Remarks
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PROJECTION SYMBOLS
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1ST ANGLE PROJECTION
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3RD ANGLE PROJECTION
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PRINCIPLES OF DIMENSIONING
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When an engineering drawing is made, dimensioning
is of vital importance.
All the dimensions necessary to make the articles
drawn must be on the drawing and they must be
presented so that they can be easily read, easily found
and not open to misinterpretation.
A neat drawing can be spoilt by bad dimensioning.
Some of the basic principles of dimensioning are given below.
1. All dimensional information necessary to describe a component
clearly and completely shall be written directly on a drawing.
2. Each feature shall be dimensioned once only on a drawing, i.e.,
dimension marked in one view need not be repeated in another
view.
3. Dimension should be placed on the view where the shape is best
seen
4. As far as possible, dimensions should be expressed in one unit
only preferably in millimeters, without showing the unit symbol
(mm).
5. As far as possible dimensions should be placed outside the view.
6. Dimensions should be taken from visible outlines rather than
from hidden lines. 47
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EXECUTION METHODS
The elements of
dimensioning include
the projection line,
dimension line, leader
line, dimension line
termination, the origin
indication and the
dimension itself.
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TERMINATION AND ORGIN INDICATOR
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Dimension lines
should show
distinct termination,
in the form of arrow
heads or oblique
strokes or where
applicable, an
origin indication.
ARRANGEMENT OF DIMENSION
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CHAIN DIMENSION PARALLEL DIMENSION
RUNNING DIMENSION CO-ORDINATE DIMENSION
The following rules must be adhered to when dimensioning:
1. Projection lines should be thin lines and should extend from about 1 mm
from the outline to 3 mm to 6 mm past the dimension line.
2. The dimension line should be a thin line and terminate with arrowheads
at least 3 mm long and these arrowheads must touch the projection lines.
3. The dimension may be inserted within a break in the dimension line or
be placed on top of the dimension line.
4. The dimensions should be placed so that they are read from the bottom
of the paper or from the right-hand side of the paper.
5. Dimension lines should be drawn outside the outline, whenever
possible, and should be kept well clear of the outline.
6. Overall dimensions should be placed outside the intermediate
dimensions.
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ILLUSTRATION OF 1-6 RULES
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7. Centre lines must never be used as dimension lines. They may be used as projection
lines.
8. Diameters may be dimensioned in one of two ways. Either dimension directly
across the circle ( not on a Centre line), or project the diameter to outside the outline. ‘
Diameter ’ is denoted by the symbol φ placed in front of the dimension.
9. When dimensioning a radius, you must, if possible, show the centre of the radius.
The actual dimension for the radius may be shown either side of the outline but should, of
course, be kept outside if possible. The word radius must be abbreviated to R and placed in
front of the dimension.
10. When a diameter or a radius is too small to be dimensioned by any of the above
methods, a leader may be used. The leader line should be a thin line and should terminate on
the detail that it is pointing to with an arrowhead or, within an outline, with a dot. Long leader
lines should be avoided even if it means inserting another dimension. The leader line should
always meet another line at an acute angle.
11. Dimensions should not be repeated on a drawing. It is necessary to put a
dimension on only once, however many views are drawn. There is one exception to this rule. If,
by inserting one dimension, it saves adding up lots of small dimensions then this is allowed.
These types of dimensions are called ‘ auxiliary dimensions ’ and are shown to be so
either by underlining the dimensions or putting it in brackets. 54
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Illustrating rules 7 – 11.
12. Unless unavoidable, do not dimension hidden detail. It is
usually possible to dimension the same detail on another view.
13. When dimensioning angles, draw the dimension lines with a
compass; the point of the compass should be on the point of the
angle. The arrowheads may be drawn either side of the dimension
lines, and the dimension may be inserted between the dimension
lines or outside them.
Whatever the angle, the dimension must be placed so that it can
be read from either the bottom of the paper or from the right-hand
side.
14. If a lot of parallel dimensions are given, it avoids confusion if
the dimensions are staggered so that they are all easier to read.
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15. If a lot of dimensions are to be shown from one projection line (often
referred to as a datum line ), either of the methods shown in Fig. 18.20 may be
used. Note that in both methods, the actual dimension is close to the arrowhead
and not at the center of the dimension line.
16. If the majority of dimensions on a drawing are in one unit, it is not
necessary to put on the abbreviation for the units used, i.e. cm or mm. In this case,
the following note must be printed on your drawing.
UNLESS OTHERWISE STATED, DIMENSIONS ARE IN MILLIMETRES
17. If a very large radius is drawn, whose centre is off the drawing, the
dimension line is drawn with a single zig-zag in it.
18. Dimensioning small spaces raises its own problems and solutions.
Some examples are shown in Fig. 18.21 . There are one or two more rules that do
not require illustrating.
19. If the drawing is to scale, the dimensions put on the drawing are the
actual dimensions of the component and not the size of the line on your drawing.
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Illustrating rules 12 – 19.
Positioning of views to be drawn
In order to space out the
views that you will draw on your
paper use the following formulas (A,
B and C are the maximum sizes of
your views) and the p and q
dimensions are the distances between
the views.
You do not have to use exact
dimensions which might complicate
the sums; use sensible
approximations for A, B and C
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LINES
Lines of different types and thicknesses are
used for graphical representation of objects.
These lines differ in:
i. Thickness and
ii. Style
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TYPES OF LINES AND THEIR APPLICATION
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TYPES OF LINES AND THEIR APPLICATION cont.
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AXIS LINES
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LETTERING
Lettering is the art of writing alphabets A,
B, C D…Z and numbers 1, 2, 3, 4,…0.
Lettering is used to describe various parts of
the drawing and to also provide other details as
may be contained in the title box.
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IMPORTANCE OF LETTERING
To undertake production work of engineering components as per the drawing, thesize and other details are indicated on the drawing.
This is done in the form of notes and dimensions.
Main Features of Lettering are legibility, uniformity and rapidity ofexecution. Use of drawing instruments for lettering consumes more time. Letteringshould be done freehand with speed.
Practice accompanied by continuous efforts would improve the lettering skill andstyle.
Poor lettering mars the appearance of an otherwise good drawing.
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IMPORTANCE OF LETTERING Cont.
Note: Lettering in drawing should be in CAPITALS (i.e., Upper-case
letters).
Lower-case (small) letters are used for abbreviations like mm, cm, etc.
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SIZE OF LETTERS
The following specifications are given for the dimensions of letters
and numerals:
The height of capital letters is taken as the base of dimensioning.
The two standard ratios for d/h, 1/14 and 1/10 are the most
economical, as they result in a minimum number of line thicknesses.
The lettering may be inclined at 15° to the right, or may be vertical.
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NOTE: The spacing between
two characters may be reduced
by half, if this gives a better
visual effect as for example
LA, TV; it then equals the line
thickness.
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Hints on Lettering
To save time, use a guide lining device
The recommended height of lettering is 3-mm
During initial learning period, make a point of concentrating on hand control
Endeavor to make your hand do what you want it to do and not otherwise.
Remember your fingers are not used to such movements, so they have to be
trained until hand control becomes effortless
Do not guess at the construction of letters and numerals. Use the sample letter
Make letters and numerals as wide as they are high with individual letters of
a word almost touching
Spacing between words is a matter of judgment and tends to improve with
practice
Lines of lettering should be spaced the same distance apart
Do not attempt to erase guide lines after lettering has been completed
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Quiz Number One
Last Name
First Name
Reg. Number
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Wednesday, October 02, 2013
Stream B
THE CONSTRUCTION OF GEOMETRIC FIGURES FROM
GIVEN DATA
Plane geometry: is the study of two-dimensional objects. The objects dealt
with plane geometry are specified with their height and width.
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Plane and Solid Geometry
A point is a non-dimensional geometric element it occurs by intersection of at
least two lines. A point has no dimensions, only location.
Solid geometry is the geometry of three-dimensional figures.
There are an endless number of plane figures but we will concern ourselves only with the more
common ones – the triangle, the quadrilateral and the better known polygons.
It is a one dimensional geometrical element occurred by moving a point along a certain
direction. There are basically vertical lines, horizontal lines and inclined lines. A line is
one-dimensional.
Drawing Lines
Lines are drawing with the help of
rulers, set square and pencils.
When drawing a line, it is a good
practice to keep his pencil vertical
and starting from one point you
slide it towards the other end.
Once a line is drawn, experts never
go through the drawn line once
again
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A point
Line 2
Line 1
A horizontal lineA vertical line
An inclined line
Lines used in engineering drawings are specified according to their
continuity and thickness.
Dividing a line into parts of equal length
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To bisect a given angle AOB
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1. With centre O, draw an arc to cut OA at C
and OB at D.
2. With centres C and D, draw equal radii to
intersect at E.
3. Line OE bisects angle AOB.
To bisect the angle formed by two converging lines.
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To bisect a given
straight line AB
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To bisect a given
arc AB
1. With centre A and radius greater than
half AB, describe an arc.
2. Repeat with the same radius from B,
the arcs intersecting at C and D.
3. Join C to D and this line will be
perpendicular to and bisect AB.
1. With centre A and radius greater than half AB,
describe an arc.
2. Repeat with the same radius from B, the arcs
intersecting at C and D.
3. Join C to D to bisect the arc AB.
To find the centre of a given arc AB
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1. Draw two chords, AC and
BD.
2. Bisect AC and BD as shown;
the bisectors will intersect at
E.
3. The centre of the arc is point
E.
To inscribe a circle in a given triangle ABC
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1. Bisect any two of the angles
as shown so that the
bisectors intersect at D.
2. The center of the inscribed
circle is point D.
To circumscribe a circle around triangle ABC
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1.Bisect any two of the
sides of the triangle as
shown, so that the
bisectors intersect at D.
2.The centre of the
circumscribing circle is
point D.
To construct an equilateral triangle, given one of the sides
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To construct an isosceles triangle given the perimeter and the altitude
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To construct a square given the length of the side
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To construct a square given the diagonal
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To construct a rectangle given the length of the diagonal and one of
the sides
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To construct a trapezium given the lengths of the parallel sides, the perpendicular
distance between them and one angle
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POLYGONS
Definitions
A polygon is a plane figure bounded by more than four straight sides.
Polygons that
are frequently referred to have particular names. Some of these are
listed below.
A pentagon is a plane figure bounded by five sides.
A hexagon is a plane figure bounded by six sides.
A heptagon is a plane figure bounded by seven sides.
An octagon is a plane figure bounded by eight sides.
A nonagon is a plane figure bounded by nine sides.
A decagon is a plane figure bounded by ten sides.
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To construct a regular hexagon given the length of the sides
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1. Draw a circle, radius equal to the
length of the side.
2. From any point on the circumference,
step the radius around the circle six
times. If your
construction is accurate, you will finish
at exactly the same place that you
started.
3. Connect the six points to form a
regular hexagon.
To construct a regular octagon given the diagonal, i.e. within a given circle
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1. Draw the circle and insert a diameter
AE.
2. Construct another diagonal CG,
perpendicular to the first diagonal.
3. Bisect the four quadrants thus produced
to cut the circle in B, D, F and H.
ABCDEFGH is the required octagon.
To construct a regular octagon given the diameter, i.e. within a given
square
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1. Construct a square PQRS, length of
side equal to the diameter.
2. Draw the diagonals SQ and PR to
intersect in T.
3. With centres P, Q, R and S draw four
arcs, radius PT ( QT RT ST) to cut
the square in A, B, C, D, E, F, G and H.
To construct a regular polygon within a given circle
1. Draw the given circle and insert a
diameter AM.
2. Divide the diameter into the same
number of divisions as the polygon has
sides.
3. With center M draw an arc, radius
MA. With center A draw another arc of
the same radius to intersect the first arc
in N.
4. Draw N 2 and produce to intersect the
circle in B (for any polygon).
5. AB is the first side of the polygon.
Step out the other sides BC, CD, etc.
ABCDE is the required polygon.95
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TANGENCY
A tangent to a circle is a
straight line which touches
the circle at one and only one
point.
These have wide applications
in Engineering Drawing
since the outlines of most
engineering details are made
up of straight lines and arcs.
Wherever a straight line
meets an arc, a tangent meets
a circle.97
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on the circumference of a circle, centre O
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To draw a tangent to a circle from any point on the circumference
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To draw a tangent to a circle from any given point A outside the circle
1. Join OP.
2. Erect a semi-circle on OP to cut
the circle in A.
PA produced is the required tangent
(OA is the radius and is
perpendicular to PA since it is the
angle in a semi-circle). There are, of
course, two tangents to the circle
from P but only one has been shown
for clarity.
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To construct a common tangent to two equal circles
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1. Join the centers of the two
circles.
2. From each center, construct
lines at 90 ° to the center line.
The intersection of these
perpendiculars with the circles
gives the points of tangency.
This tangent is often described
as the common exterior tangent.
To construct the common interior (or transverse or cross) tangent to two
equal circles, centres O and O 1
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1. Join the centers OO 1 .
2. Bisect OO 1 in A.
3. Bisect OA in B and draw a
semi-circle, radius BA to cut
the circle in C.
4. With center A and radius
AC, draw an arc to cut the
second circle in D.
CO is the required tangent.
To construct the common tangent between two unequal circles, centres O and
O 1 and radii R and r , respectively
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1. Join the centers 0 and 01 of the
circles.
2. Bisect 0 01 in A and draw a semi
circle of radius AO
3. Draw a circle, center O, radius R-r,
to cut the semi circle in B.
4. Join OB and produce to cut the
larger circle in C.
5. Draw O1D parallel to OC.
6. Join C to D and CD is the required
tangent.
To construct the common internal tangent between two unequal circles, centres
O and O 1 and radii R and r , respectively
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1. Join the centers OO1 .
2. Bisect OO1 in A and draw
a semi-circle, radius OA.
3. Draw a circle, center O,
radius R+r , to cut the semi-
circle in B.
4. Join OB. This cuts the
larger circle in C.
5. Draw O1 D parallel to OB.
CD is the required tangent.
To draw a curve of given radius to touch two circles when the circles are outside the radius
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Assume that the radii of the given circles are 20 and 25
mm, spaced 85 mm apart, and that the radius to touch
them is 40 mm.
With center A, describe an arc equal to 20 + 40 = 60
mm.
With center B, describe an arc equal to 25 + 40 = 65
mm.
The above arcs intersect at point C. With a radius of
40 mm, describe an arc from point C as shown, and
note that the points of tangency between the arcs lie
along the lines joining the centers AC and BC.
It is particularly important to note the position of the
points of tangency before lining in engineering
drawings, so that the exact length of an arc can be
established.
To draw a curve of given radius to touch two circles when the circles are inside the radius
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To draw a radius to join a straight line and a given circle
Assume that the radius of the given circle is 20 mm and
that the joining radius is 22 mm.
With center A, describe an arc equal to 20 + 22 = 42
mm.
Draw a line parallel to the given straight line and at a
perpendicular distance of 22 mm from it, to intersect the
arc at point B.
With center B, describe the required radius of 22 mm,
and note that one point of tangency lies on the line AB
at C; the other lies at point D such that BD is at 90 to the
straight line.
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To draw a radius which is tangential to given straight lines
Assume that a radius of 25 mm is
required to touch the lines shown
in the figures.
Draw lines parallel to the given
straight lines and at a
perpendicular distance of 25 mm
from them to intersect at points A.
As above, note that the points of
tangency are obtained by drawing
perpendiculars through the point
A to the straight lines in each
case.
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