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Engineering drawing
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MCE216L Engineering Drawing MCE216L Engineering Drawing and Workshopand Workshop
Lecture #3Lecture #3
Orthographic ProjectionOrthographic Projection
Eng. Rami AliEng. Rami AliFall 2015Fall 2015
Line Convention
Multiview drawing (Review )
1st and 3rd Angle projections
Multiviews using Miter line
Contents
Image on a projection plane (or view) depends on a relative orientation between an object and a plane.
Rotate
Tilt
Multiview drawingshows a 2D view of an object.
Axonometric drawing
shows a 3D view ofan object.
View
View comparison
Pictorial drawing
Perspective drawing
Multiview drawing
Difficult to create
Easy to understand Shape and angle distortion
Object looks morelike what our eyesperceive.
Size and shape distortion
Right angle becomes obtuse angle.
Circular hole becomes ellipse
Distortedwidth
Accurate represents an object’s details, i.e. size and shape.
Require an enough practiceto visualization.
Advantage DisadvantageType
Multiview drawing is a set of related images that are created by viewing the object from a different direction.
Width Depth
Height
Width
Hei
ght
Depth
Dep
th
Adjacent view(s)is needed tofulfill the objectdescription.
Multiview Drawing
1. Revolve the object with respect to observer
Methods
2. The observer moves around the object.
Front view Right side view
Top view
Right sideview
Top view
play play
Frontview
Glass box concept
Glass box : Revolution of the planes of projection
Bottom view
Left side view
Rear view
HeightWidth
Dep
th
Relative orientation of views
Left side view Right side view
Bottom view
Top view
Rear view
Front view
Summary : Problem solving steps
1 2
3 4
Given
INTERPRETING VIEWSINTERPRETING VIEWSOne method of interpreting sketches is to reverse the
mental process used in projecting them.
ALIGNMENT OF VIEWSALIGNMENT OF VIEWSAlways draw views in the “standard” arrangement...
Because CAD makes it easy to move whole views, it is tempting to place views where they fit on the screen or plotted sheet and not in the standard arrangement. This is not acceptable.
3D CAD software that generates 2D drawing views as projections of the 3D object usually has a setting to select from third-angle or first-angle projection. Check your software if you are unsure which projection methods are available.
Third-Angle ProjectionThird-Angle Projection
To understand the two systems, think of the vertical and horizontal planes of projection, as indefinite in extent and intersecting at 90° with each other; thefour angles produced are called the first, second, third, and fourth angles (similar to naming quadrants on a graph.) If the
object to be drawn is placed below the horizontal plane and behind the vertical plane, as in the glass box you saw earlier, the object is said to be in the third angle. In third-angle projection, the views are produced as if the observer is outside, looking in.
First-Angle ProjectionFirst-Angle ProjectionIf the object is placed above the horizontal plane and in front of
the vertical plane, the object is in the first angle.
The biggest difference between third-angle projection and first-angle projection is how the planes of the glass box are unfolded.
Transferring Depth DimensionsTransferring Depth Dimensions
You can transfer dimensions between the top and side views either with dividers or
with a scale.
The depth dimensions in the top and side views must correspond point-for-point. When using CAD or instruments,
transfer these distances accurately.The use of MITER LINE provides you fast and accurate method of constructing the 3rd view once two views are established.
Transferring a depth : miter line
miter line 45o
Extension lines
Object featuresEdge is a line that represent the boundary between two faces of an object. Surface limit is a line that represents the last visible part of the curve surface.
Prism Cylinder Sphere
No edges!
Surface is an area that are bounded by edges or surface limit. Surface can be plane or curve.
These features will appear as lines in a multiview drawing.Note
Class activity : Object’s features
12
34
5
6
7
8
Identify name of the featuresdenoted by a NO. 1 to 9?
1
2
3
4
5
6
7
8
Edge Surfacelimit
Surface
Skip test Next slideReset all
B
AF BF BRAR
AT
BT
Projection of a normal line
A
Play
Glass box concept Multiview drawing
AR
BR
AT
BT
AF BF
Projection of a normal plane
Play
Glass box concept Multiview drawing
Projection of an object
Play
Glass box concept Multiview drawing
Do the same procedures forall remaining edges (or planes)
Hidden line is usedto show existence of
a hidden edge.
Projection of an inclined line
Play
Glass box concept Multiview drawing
AF
BF
AF
B
A
BF
AR
BR
AR
BR
AT
BT
AT
BT
Projection of an inclined plane
Play
Glass box concept Multiview drawing
Projection of an obliqued line
Play
Glass box concept Multiview drawing
AF
B
A
BF
AR
BR
AT
BT
AF
BF
AR
BR
AT
BT
Projection of an obliqued plane
Play
Glass box concept Multiview drawing
Projection of a curve line
Play
Glass box concept Multiview drawing
AFBF
CF
BR
AT
BT
CT
AR
CR
B
AC
AFBF CF BRAR CR
AT
BT
CT
Projection of a curve surface
Play
Glass box concept Multiview drawing
VIEWS OF SURFACESVIEWS OF SURFACESThere are terms used for describing a surface’s orientation to the plane of projection. The three orientations that a plane surface can have to the plane of projection are normal, inclined, and oblique.
Note how a plane surface that is perpendicular to a plane of projection appears on edge as a straight line
ANGLESANGLESIf an angle is in a normal plane (a plane parallel to a plane of projection) it will show true size on the plane of projection to which it is parallel.
If a flat surface is viewed from several different positions, each view will show the same number of sides and a similar shape. This consistency of shapes is useful in analyzing views.
Example
Projection of an object havingcurved surface and plane
In the case of intersection, an edge exists and becomes a line in a multiview drawing
Curved surface can either tangent or intersect with an adjacent plane or adjacent curve surface.
In the case of tangential, there is no edge and line in a multiview drawing
I
I
T
T
T
I
Examples
Play
2
3
Play
Play
4
Play
1
Examples
Play
5 6
Play
Examples
Play
Play
7 8
9
Play
Play
10
No line exists
Line Convention
Line convention
Precedence of coincide lines
Hidden line drawing
Center line drawing
Precedence of line
When lines coincide witheach other, the moreimportant lines cover upthe other lines.
Order of importance(from high to low) is- visible line- hidden line and- center line.
Line convention
Play
What is an appropriate line type to replace the lines NO. 1-4?
1
2
3
V H C
Skip test Next slideReset all
“V” denotes visible line
“H” denotes hidden line
“C” denotes center line
Class activity : Precedence of lines
12 3
4
4
Hidden line drawingHidden line should join a visible line, except it extends from a visible line.
joinspace
join
space
spacespace
Hidden line drawingIntersection between hidden lines should form L, T, V or Y corner.
L T
inside
VY
L T
A curve hidden line should start on a center line.
Hidden line drawing
Line convention
Center line drawing
In a circular view, short dash of a center line should cross at the center of the circle or arc.
Center line should always start and end with long dash.
Center line should not extend between views.
Leave space Leave space
Play Play
3~4 mm
3~4 mm
Center line drawingFor a small hole, a center line is presented as a thin continuous line.
Leave a gap when centerline forms a continuation with a visible or a hidden line.
Play
Leave space Leave space Leave space
Line convention
Class activity : Hidden line drawing
correct wrong
correct wrong
Skip test Next slideReset all
MultiViews ExamplesMultiViews Examples
Class WorkClass WorkDraw the Front, Plan, and side multiviews (orthographic projections) for the following parts
1 Using 3rd Angle method 2 Using 1st Angle method 1 Using 3rd Angle method