What
is Engineering Graphics?
A
set of rules and guidelines that help you create an Engineering
Drawing.
What
is an Engineering Drawing?
A
drawing that communicates an idea or design.
→Mechanical
Engineers (factory/manufactured
parts)
•Detailed
drawing of a part that needs to be machined.
→Electrical
Engineers (appliances
to power transmission)
•A
circuit schematic.
•Circuit
board layout. (electronics)
→Civil
Engineers (topography/landscapes)
•Plans
for a bridge.
•Road
layout. bb
Orthographic Projection
→An orthographic projection is a 2-D representation of a 3-D object.
→A system of drawings that represent different sides of an object.
→Project edges perpendicular to planes of projection
→Represent a shape using 2 or more views
→Gives enough information to manufacture the part
3D is the ISOMETRIC VIEW 2D is the ORTHOGRAPHIC VIEW
SIX PRINCIPLE VIEWS
The
6 principal views are created by looking at the
object, straight on, in the directions indicated.
How
do we create the 6 principal views?
The
Glass Box Method
Consider
a pair of dice – each number is a view.
Choose one number for the front and then determine the remaining five
views.
The
object is placed in a glass box.
Left, Front, Right, Rear, Top, Bottom
The
sides of the box represent the 6 principal planes.
The
image of the object is projected on the sides of the box.
VISUALIZE !!!
Things
to notice!
→The
projection planes (SIDES
OF BOX)
→The
projectors (DASHED
LINES)
→How surfaces A and B are projected. (Parallel FULL/non-parallel
SHORTENED)
The
box is unfolded creating the 6 principal views.
Notice the hidden lines which show features that are not directly visible from that particular view.
EXERCISE . . .
Label
the 5 remaining principal views with the appropriate view name. Right, Left, Rear, Top and Bottom.
Standard Views
When
constructing an orthographic projection, we need to include enough views to completely describe the true shape of the part.
→Complex
part = more views are required
→Simple
part = less views are required
The
standard views used in an orthographic projection are;
→Front
view
→Top
view
→Right
side view
The
remaining 3 views usually don’t add any new information (but sometimes they do).
How
many views do we need to completely describe a block?
Front
view shows THE MOST features.
All
other views are based upon the orientation chosen for the front view.
Front view usually contains the least number of hidden lines.
How
many views do we need to completely describe a block?
Front View
The
front view shows the most features or characteristics of the object.
→It
usually contains the least amount of hidden lines.
→The
front view is chosen
first and
the other views are based on the orientation of the front view which also
determines the VIEW
ALIGNMENT.
View Alignment
The
top
and front
views are aligned vertically (UP AND DOWN) and share the same
width dimension.
Width (vertical alignment) and
height (horizontal alignment)
Line
type and line
weight provide valuable information to the print
reader.
For
example, line type and weight can answer the following questions.
→Is
the feature visible or hidden from view?
→Is
the line part of the object or part of a dimension?
→Is
the line indicating symmetry (same
on both sides of
the line)?
There
are four commonly used line types; (there are more than four types of lines – but these are those which
are most COMMONLY used in engineering drawings).
→continuous
→hidden
→center
→phantom
Some
lines are more important than others. Importance is indicated by line weight or
thickness.
→The
thicker the line, the more important it is.
Visible lines:
→Visible
lines represent visible edges and boundaries.
→Continuous (no breaks/dashes) and thick (0.5
- 0.6 mm).
Hidden lines:
→Hidden
lines represent edges and boundaries that cannot be seen.
→Dashed
and medium thick (0.35
- 0.45 mm).
Center lines:
→Represent
axes
of symmetry.
→Long dash – short dash and
thin (0.3 mm).
Phantom line:
→Phantom
lines are used to indicate imaginary features.
•alternate
positions of moving parts
•adjacent
positions of related parts
→The
line type is long dash – short dash – short dash
and the line weight is usually thin
(0.3 mm).
Dimension and Extension lines:
→Dimension
and extension lines are used to show the size of an object.
•In
general, a dimension line is placed between two extension lines and is
terminated by arrowheads,
which indicates the direction and extent of the dimension.
→The
line type is continuous
and the line weight is thin
(0.3 mm).
Cutting Plane line:
→Cutting
plane lines are used to show where an imaginary cut has
been made through the object in order to view interior features.
→The
line type is phantom
and the line weight is very thick (0.6
to 0.8 mm).
→Arrows
are placed at both ends of the cutting plane line to indicate the direction of
sight.
Section line:
→Section
lines are used to show areas
that have been cut
by the cutting plane.
→Section
lines are grouped in parallel line patterns and usually drawn at a 45° angle.
→The
line type is usually continuous
and the line weight is thin (0.3
mm).
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