Engi 1504 – Graphics
Lecture 6: Descriptive Geometry II
 Properties of planes
 Midterm issues
 Class assignment # 7
Course: Engineering Graphics 1504
Memorial University of Newfoundland
Sheet
1
Properties of Planes

Two limiting cases of a plane:
– True shape
– Edge view

Can be used to solve any problem involving
planes
Course: Engineering Graphics 1504
Memorial University of Newfoundland
Sheet
2
Properties of Planes


At least three lines are required to define a
plane
Edge view must be found before a true shape
can be found
Course: Engineering Graphics 1504
Memorial University of Newfoundland
Sheet
3
Finding the Edge view of a Plane



A plane will be seen as an
edge if any line in it is seen
as a point.
It is often easier to add a line
(where we want it) than to
use an existing line
Recall: a line must show true
length before it can be seen
as a point
Course: Engineering Graphics 1504
Memorial University of Newfoundland
Sheet
4
Finding the Edge view of a Plane




We can find the true length of any
line (AB, BC, or CA) using an
auxiliary plane parallel to it.
Then we can find the line as a point,
which will show the plane as an
edge.
This requires two auxiliary planes –
there is an easier way!
We will create a True length line in
the plane.
Course: Engineering Graphics 1504
Memorial University of Newfoundland
Sheet
5
Finding the Edge view of a Plane



Note: none of the given lines
are parallel to a folding line,
and hence not true length.
So we construct a true length
line in the plane and then
show it as a point.
This requires only one
auxiliary view
Course: Engineering Graphics 1504
Memorial University of Newfoundland
Sheet
6
Finding the Edge view of a Plane



Draw a line in the plane parallel True Length
to a folding line (say in the front
view).
Project the endpoints into the
top view. This line is true length
Now we have a true length line,
so all we have to do is show it
as a point.
Course: Engineering Graphics 1504
Memorial University of Newfoundland
X2
x1
Sheet
7
Edge View of a Plane cont.

To find the point view
of AX, we construct a
folding line
perpendicular to AX
and project onto
auxiliary plane 3
3
a3x3
2
D
Point
view
D
Course: Engineering Graphics 1504
Memorial University of Newfoundland
Sheet
8
Edge View of a Plane cont.

Project B and C onto
plane 3 and join the
points to show plane
ABC as an edge
Course: Engineering Graphics 1504
Memorial University of Newfoundland
Sheet
9
True Shape of a Plane



If we place an auxiliary plane parallel to the
edge view, then the plane can be seen as
true shape.
Recall: An edge view must be found first
So we place an auxiliary plane parallel to the
edge view and project the plane onto it
Course: Engineering Graphics 1504
Memorial University of Newfoundland
Sheet 10
True Shape of a Plane




Draw the plane in edge view.
Place a folding line parallel to the edge
view.
Project all points onto the auxiliary plane
(plane 4 in this case) and join them.
Recall: the distance from the folding line is
found from the view adjacent to the edge
view (plane 2 here)
Course: Engineering Graphics 1504
Memorial University of Newfoundland
Sheet 11
Plane
shows true
shape
Course: Engineering Graphics 1504
a4
b4
c4
Memorial University of Newfoundland
Sheet 12
The Slope of a Plane




The slope of a plane is the angle it make
with the horizontal.
Slope is seen only in the front or profile
view (the elevation views)
Recall: slope can only be determined from
a true length line.
So, the TL line used to find the edge view of
the plane must be in the top view so that
the edge of the plane appears in the
horizontal view
Course: Engineering Graphics 1504
Memorial University of Newfoundland
Sheet 13
The Slope of a Plane



Create a TL line in
the horizontal view
Find the edge view of
the plane
Measure the angle it
makes with the
horizontal
Course: Engineering Graphics 1504
Memorial University of Newfoundland
54o slope
Sheet 14
The Strike of a Plane


The strike of a plane
is the angle that a
true length line in the
plane makes with the
North (top view)
So strike is the
bearing of the
horizontal line AX
Course: Engineering Graphics 1504
N
strike
Memorial University of Newfoundland
54o slope
Sheet 15
Summary
Find edge view of a plane:
1.
2.
Draw a line parallel to a folding line and project the line into the
adjacent view, where it will be true length
Find a point view of this line and project other points in the plane.
The plane will appear as an edge
Find true shape of a plane:
1.
2.
Find edge view of a plane and create an auxiliary view parallel to
the edge view
Project the points defining the plane onto this auxiliary view. The
plane will be true shape
Course: Engineering Graphics 1504
Memorial University of Newfoundland
Sheet 16
Break Time

Take 5 minute break
Course: Engineering Graphics 1504
Memorial University of Newfoundland
Sheet 17