ENGN103 Engineering Drawing geometric constructions Lecture 2

Draw and mark the dimensions: Circle of Radius 30mm. And mark the radius. Circle of diameter 25mm. Mark the diameter. Rectangle of length 100mm and breadth 60mm. Square of side 40mm. Triangle of sides 80mm, 65mm and 60mm. Triangle of side 65mm and angle 55degree and 70degree. Hexagon of sides 40mm.

Draw a line of 65mm and bisect the line. Draw a line of 70mm and divide into 5 equal parts. Draw a line of 90mm and divide in a ratio of 3:4 Draw an angle of 75degree and bisect the angle. Draw an arc and find the center of the arc. Construct a triangle of sides 75mm, 65mm and 70mm. Inscribe a circle inside the triangle. Mark the radius. Construct a triangle of sides 35mm, 40mm and 55mm. Circumscribe a circle around the triangle. Mark the radius. Construct an ellipse of major axis 70mm and minor axis 40mm.

To bisect a line Draw the given line AB, with centers A and B and radius R greater than half of AB, draw arcs to intersect a t C and D. Join CD, when E will be the mid point of the line. Also CD will be perpendicular to AB

A B

A B

A B

C A B D

To bisect an angle Draw the given angle ABC and from the apex B draw an arc of radius R to cut AB and CD at D and E. R may be any convenient radius. With D and E as centers and radius R’, draw two arcs to meet F. Again, R’ may be any convenient radius. Join FB to bisect the angle.

A B C

A D B E C

A D B E C

A D B E C

A O D B E C

To inscribe a circle in a triangle. Draw the given triangle ABC and bisect an two angles. Produce the bisectors to intersect at O, which is the center of the inscribe circle.

To draw the circumscribing circle of a triangle. Draw the given triangle ABC. Bisect any two of the sides and produce the bisectors to intersect at O. O is the center of the circumscribing circle.