INTRODUCTION TO AUTOCAD 1
TECHNICAL DRAWING MEC 112 week 1
WEEK 14 SURFACE DEVELOPMENT
14.1: Right cone
Fig (14)
To develop a pattern for a right cone the following steps are to be followed:
1- draw the front and top views of the cone
2- divide the circle of the top view into 12 equal and number them from 1 to
12 .
3- on the development area , use "O" as a center, then draw an arc of radius
(s) which is the true length of the sloping edge of the cone ( slant length ) .
4- use the divider to step off (12) equal spaces along the arc , each equal the
distance between the two consecutive numbers on the circle ( approximate
method ) or πD/12 ( accurate method ) .
5- join the first and last element lines (0-11) and (0-12) . the sector represents
the true pattern for the cone .
INTRODUCTION TO AUTOCAD 1
TECHNICAL DRAWING MEC 112 week 1
Fig (14.1)
There are many types of right pyramids, see below Fig.(28) . According to the shape
of the base, they can be classified to:
a)
b)
c)
Square pyramid.
Rectangular pyramid.
Hexagonal pyramid.
a-Square
Pyramid
b-Rectangular
Pyramid
c-Hexagonal
Pyramid
Fig.(14.2)
When developing a pyramid, it is necessary to find the true length of its sloping edge
(corner). This depends upon the position of the pyramid. When the pyramid is
INTRODUCTION TO AUTOCAD 1
TECHNICAL DRAWING MEC 112 week 1
positioned as shown in the above Fig. (28a) then line OA in the front view is the true
length of the sloping edge.
However, when the pyramid is positioned as shown in Fig. (28b) then it is important
to deduce the true length of the edge of the pyramid.
True length
To find the true length of pyramid edge the following steps are to be followed:
1.
In the Top view, with a radius OA and centre O, revolve the line OA until it is
horizontal OA".
2.
Project the end of the line OA" up to meet a horizontal line through the front
view of A at point A", in next Fig. (28b).
3.
Join this point of intersection with the front view of O.
4.
The true length of the edge is the line OA".
Fig.(14.3)
INTRODUCTION TO AUTOCAD 1
TECHNICAL DRAWING MEC 112 week 1
14.2 Pattern Development
To develop the pattern of the right pyramid, the following steps are to be
followed:
1)Draw the front and top views
1) Find the true length of the pyramid edge .
2) By using the true length as a radius draw an arc of a suitable length .
3) With a radial equals to the side of the pyramid base , mark off the four side of
the base along the drawn arc (One is to be halved to keep the seemed joint in
the middle of the pyramid ).
4) Joint the dividing points along the arc , in sequence , with straight lines ( SA,
AB , BC , ….,DS) .
5) Joint the dividing points along the arc with the apex "O" to get the pattern .
Fig.(14.4)
INTRODUCTION TO AUTOCAD 1
TECHNICAL DRAWING MEC 112 week 1
14.3 TASK (7)
Draw the development pattern for rectangular pyramid .
Fig.(14.5)