Department
of
Technological
Education
Graphic Communication
Nairn Academy
Department of Technological Education
Cut Oblique Cone
The Elevation of a cut Oblique
Cone is shown.
Draw the Plan of the cone.
Draw the Surface
Development of the cone.
O
PLAN
O
ELEVATION
Department of Technological Education
Drawing Generators to Apex
Start by drawing the circle
shape of the cone in Plan.
Divide the Plan into 30o
parts, project the points
down to the Front Elevation
and number each of the
points found.
12
2
1O
9
3
O
8
4
7
5
6
2/4
3
1/5
12/6
PLAN
11/7
9
10/8
Project generators for these
lines to the apex of the cone
on the Plan.
Repeat this process for the
Front Elevation.
1
11
O
ELEVATION
Department of Technological Education
Drawing Cut in Plan
Find the point where each
generator on the Elevation
passes through the top cut.
12
Project these points back up
to the appropriate generator
on the Plan.
1
11
2
1O
9
3
O
8
4
7
5
6
2/4
3
1/5
12/6
11/7
PLAN
9
10/8
Draw a smooth curve
through each of the points
found and darken in the
remainder of the outlines.
O
ELEVATION
Department of Technological Education
Finding True Length Lines
Before you can start drawing the
Surface Development of the
Oblique Cone, it is necessary to
find the True Length of each of
the generators.
Angled lines are now drawn on
the Elevation to point ‘O’. These
lines are the True Lengths of
each of the generators.
2/4
1/5
12/6
11/7
10/8
9
1/5
12/6
11/7
10/8
9
3
3
2/4
9
O
8
4
7
5
6
2/4
3
3
1/5
PLAN
12/6
Each generator is now projected
down to the base of the
Elevation. (the base in this
drawing is actually the top
surface.
2
11/7
This process is normally done to
the side of the existing views for
clarity.
1
1O
9
10/8
Each Plan generator needs to be
rotated to be horizontal with
point ‘O’ using point ‘O’ as the
centre of the rotation.
12
11
O
ELEVATION
Department of Technological Education
Drawing Surface Development
To draw the Surface
Development it is wise to use
two pairs of compasses if
possible.
12
O
9
10/8
11/7
12/6
1/5
3
3
2/4
9
O
3
3
8
4
7
5
6
2
4
9
10/8
11/7
12/6
1/5
2/4
2/4
3
3
1/5
PLAN
12/6
For each subsequent point two
arcs need to be drawn – one for
the True length dimension and
the other for the 30o segment
dimension.
2
1O
11/7
Starting with the longest
generator, draw a vertical line
and measure the length of the
O9 True Length line.
1
11
9
10/8
One can be set to the longer
True Length sizes and adjusted
when required, with the other
set to the smaller 30o segment
distance from the Plan.
1
5
12
6
11
7
8
Place a small dot where the two
arcs cross to locate a point on
the edge and number the points.
O
ELEVATION
9
10
Department of Technological Education
Drawing Cut on Development
To complete the Development it
is necessary to find the points for
the cut top surface.
The points on the Elevation
should be projected onto the
appropriate True Length line.
12
O
9
10/8
11/7
12/6
3
3
1/5
9
2/4
2
1O
Measure the dimensions from ‘O’
to each cut point and transfer
this size to the correct generator
on the Development.
O
3
3
8
4
7
5
6
2
4
These sizes should be measured
on the Plan and transferred to
the Development.
9
10/8
11/7
12/6
1/5
2/4
2/4
3
3
1/5
12/6
11/7
PLAN
9
10/8
Two other points need to be
found – the two end points of
the cut.
1
11
1
5
12
6
11
7
Note that in this situation the
dimension is measured from
point 6 towards 5 (and 12 to 1)
as this gives the larger of the two
alternatives and is more accurate
8
O
ELEVATION
9
10
Department of Technological Education
The Completed Drawing
To complete the drawing the
curves and the outlines
should be darkened in.
12
1
11
O
9
10/8
11/7
12/6
3
3
1/5
9
2/4
2
1O
O
3
3
8
4
7
5
6
2
4
9
10/8
11/7
12/6
1/5
2/4
2/4
3
3
1/5
12/6
11/7
9
10/8
PLAN
1
5
12
6
11
7
8
O
ELEVATION
9
10
PowerPoint Presentation produced by John McRae, Nairn Academy 2003