Engineering H191 - Drafting / CAD
Topics For Today
Drawing No. 16 is due now
Lab report due on at the beginning of your lab period
Descriptive Geometry

Read BTG Chapter 11, Section 5
Autumn Quarter
Gateway Engineering Education Coalition
Lect 9
P. 1
Engineering H191 - Drafting / CAD
Descriptive Geometry
Graphics representation of the plane, solid and analytical
geometry used to describe real (or imagined) objects
It is the foundation, the underlying science of engineering
technical drawings
Traditional methods for solving spatial design problems:
 Direct view
 Revolution
 Fold-line
Autumn Quarter
Gateway Engineering Education Coalition
Lect 9
P. 2
Engineering H191 - Drafting / CAD
Conventions and Definitions
Lines and planes extend to infinity while we work with a
small portion which we define.
Lines and planes can be extended.
Dihedral angle – The angle between two planes – smaller of
the two. It can be found by finding the line of intersection
and looking at the line of intersection as a point.
Angle between a line and plane – This requires a view in
which the plane is an edge and the line is true length.
Autumn Quarter
Gateway Engineering Education Coalition
Lect 9
P. 3
Engineering H191 - Drafting / CAD
Line Types
Vertical, horizontal, or inclined

TL
Top
TL

Front
TL
If a line is parallel to one of the principal projection planes,
it’s called a principal line
 Frontal (parallel to and true length in a frontal plane)
 Horizontal
 Profile
Autumn Quarter
Gateway Engineering Education Coalition
Lect 9
P. 4
Engineering H191 - Drafting / CAD
Plane Types
Horizontal Plane (True Size Projection In Top Or Bottom
Views)
BT
CT
TS
Top
AT
AF
Autumn Quarter
BF
CF
Gateway Engineering Education Coalition
Front
Lect 9
P. 5
Engineering H191 - Drafting / CAD
Descriptive Geometry - Planes
Vertical plane (appears as edge in top and bottom views)
Profile (appears as edge in front view and is parallel to
profile projection plane)
Frontal (appears as edge in profile view and is parallel to
frontal projection plane)
Autumn Quarter
Gateway Engineering Education Coalition
Lect 9
P. 6
Engineering H191 - Drafting / CAD
Descriptive Geometry - Planes
F
N
M
Top
L
A
B
C
D
D
B
E
D
F
L
M
TS
N
C
A
Inclined
(Not TS!!)
Autumn Quarter
F
TS
E
Frontal
Gateway Engineering Education Coalition
E
Profile
Lect 9
P. 7
Engineering H191 - Drafting / CAD
Descriptive Geometry - Planes
Oblique (Not True Size Projection In Principal Views)
Y
Z
X
X
Z
Y
Autumn Quarter
Gateway Engineering Education Coalition
Lect 9
P. 8
Engineering H191 - Drafting / CAD
Key to Descriptive Geometry
Top
Know the location of the origin (0,0,0)
Front
Right Side
Autumn Quarter
Gateway Engineering Education Coalition
Lect 9
P. 9
Engineering H191 - Drafting / CAD
Descriptive Geometry with AutoCAD
Download a blank3d template – 4 viewports, 3D
construction, world coordinates, cursor tracking – world
Layout mode – Transferring the model to paper – tab at the
bottom of screen
The layout and the model or construction mode are all part
of one file.
Autumn Quarter
Gateway Engineering Education Coalition
Lect 9
P. 10
Engineering H191 - Drafting / CAD
Today’s Assignment
Download template from Web CT
Dwg 17 – SGAC-3-1
 Space Geometry in AutoCAD
 Pierce point of a line and a plane
 Due at end of class today
 Consult handout – steps for solving problems in
AutoCAD are provided
Dwg 18 – SGAC-3-2
 Space Geometry in AutoCAD
 Intersection of Planes
 Due at beginning of next lecture
 Consult handout– steps for solving problems in
AutoCAD are provided
Autumn Quarter
Gateway Engineering Education Coalition
Lect 9
P. 11