INTRODUCTION TO
TECHNICAL DRAWINGDr. Mark Yuly
PHYS 215 Statics and Engineering Design
Visualization and Drawing
Visualization – ability to create and manipulate mental image.
Drawing – ability to put it on paper.
Why is this important?
I. Images can be visualized by showing how an
objects geometric elements are related.
Faces (“planes”) Reflect the light that we see.
Edges (“lines”) Two faces intersect.
Abrupt change in contrast.
Vertices (“points”) Three or more edges intersect.
Curves Surface limits.
face
edge
vertex
Surface limit
Example:
Semi-Cylinder
II. Pictorial Projections
A. Perspective Projection
1. True depth perception.
2. Most natural looking.
3. Hard to sketch quickly.
Projection
plane
object
II. Pictorial Projections
B. Parallel Projections
1. View at ∞.
2. Projection lines are ∥.
3. Easier to use.
III. Parallel Projections
A. Orthographic Projection
1. LOS is always ⊥ to projection plane.
2. Only see one side of object at a time.
III. Parallel Projections
B. Oblique Projection
1. LOS is intersects
projection plane at
angle other than
90°.
2. Front face is true-
size, other faces are
distorted.
3. Use when most detail
on front face.
III. Parallel Projections
C. Isometric Projection
1. Rotate object so
front face is not ∥ to
projection plane.
2. Use for features on
multiple sides.
V. Orthographic
Projections
A. Formed by taking orthographic projection of each side – then “unfolding”…
B. Views:TopFrontRight
Bottom RearLeft
Only use as many as needed.
C. Hidden linesUse views with fewest hidden lines.
} standard
V. Orthographic projectionsD. Standard location and orientation.
front
rear left
bottom
top
right
V. Orthographic
projections
E. Types of lines
Also: Construction lines
1. Preliminary layout work.
2. Very thin and light.
3. Avoid having to erase.
http://www.ic.arizona.edu/ic/ce210/lines.htm
V. Orthographic
projections
E. Types of lines
Alphabet of Lines
Name Line Description Sizes Examples
Construction
Line
A lightly drawn line
that shows the shape of
an object.
A light thin solid
line.
Border
Line
A very thick line that
frames the drawing.
A very thick solid
line.
Visible
Object
Line
A thick line that shows
the form of an object.
A thick solid line.
Hidden
Object
Line
A thin line that has
broken dashes. It
shows a hidden edge.
Dashes are 3 mm
long with 0.75 mm
spaces.
Centre
Line
A thin line with long
and short dashes. It
indicates the centre of
objects and shows that
an object is symmetrical
about a line.
Long dashes are
25 mm long and the
short dashes are 3
mm with 1.5 mm
spaces.
Extension
Line
A thin line used to
extend the size of the
object so that the
dimension can be
placed near the view.
A thin solid line that
projects from an
object. Starts about
1.5 mm after object
line and ends about
3 mm beyond the
last dimension line.
Dimension
Line
A thin line with
arrowheads on each end
that touch the extension
line. It is opened for
the dimension.
A thin solid line the
length of each
dimension. Should
start at about 10 mm
away from the
object line.
50
30
Leader
Line
A thin line with an
arrowhead on one end
and on the other end is a
dimension or note.
A thin solid line
used to show the
parts related to the
note or dimension.
www.ijs.k12.nf.ca/Tech_Page/grade8_tech/Alphabet%20of%20Lines.doc
The Plan This week: 2D drawings
Download AutoCAD
Download “AutoCAD 2020 Tutorial First Level” sample chapter
Complete the two drawings in the tutorial.
Look up how to add dimensions (Google).
Next week: 3D drawings in Inventor
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