05 - mech1009y - construction.of.geometric.figures - (ln)

7/23/2019 05 - MECH1009Y - Construction.of.Geometric.figures - (LN)

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Construction Of

Geometric FiguresTangency

Blending of Lines& Curves


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(ka) | MECH1009Y | Engineering Graphics & Computer Aided Drafting Page | 2

1Construction of Geometric Figures

Engineering drawings require the use of a number of simple

geometrical constructions and engineering curves. The

constructions are mostly based on simple theorems of plane

geometry. A few methods are illustrated hereafter.

1.1Dividing a straight line into a given number of

equal parts

(DIVISION BY GEOMETRIC METHOD)


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1.2Dividing a line in the ratio 1:3:4

1.3Constructing parallel lines

1.4Bisecting a line


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1.5 Drawing a perpendicular from a point on a line

1.6 Drawing a perpendicular from a point to a line

1.7 Bisecting an angle


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1.8 Bisecting the angle formed by two converging lines

1.9 Constructing a 60 angle

Construct 30, 90 and 45 angles.


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1.10 Constructing any given regular polygon, given

the length of a side

1.10.1 Method 1


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1.10.2 Method 2


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1.10.3 Method 3


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2Tangency

A tangent to a curve is a straight line that touches the curve at

one point only. Particular attention is devoted here to theconstruction of tangents to circles.

2.1Tangent to a circle from any point on the

circumference

2.2Tangent from a point P to a circle centre 0


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2.3Constructing an external tangent to two circles


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2.4Constructing an internal tangent to two circles


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3Blending of Lines & Curves

A curve will only blend properly with another curve or line when

the centre of the curve has been correctly found. If the centre is

found exactly, the curve is bound to blend exactly.

3.1Blending of an arc (radius r) with straight lines

meeting at right angles


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3.2Blending of an arc (radius r) with straight lines

meeting at any angles

3.3Blending of an arc (radius r) passing through a

point P, with a straight line


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3.4Blending of an arc (radius R) with a line and a

circle (centre B, radius r)

3.4.1Option 1

3.4.2Option 2

05 - mech1009y - construction.of.geometric.figures - (ln)

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