Diapositiva 1

Lecture 4: Orthographic projections, Multiview drawing 1ENS 207 engineering graphics1PROJECTION THEORYThe projection theory is based on two variables:1) Line of sight2) Plane of projection (image plane or picture plane)The projection theory is used to graphically represent3-D objects on 2-D media (paper, computer screen). 2Orthographic projection is a parallel projection techniquein which the parallel lines of sight are perpendicular to theprojection planeMEANING

Line of sight is an imaginary ray of light between anobservers eye and an object.Line of sightParallel projectionLine of sightPerspective projectionThere are 2 types of LOS :parallelconvergeand5Which Views to Present?General GuidelinesPick a Front View that is most descriptive of object Normally the longest dimension is chosen as the width (or depth)Most common combination of views is to use: Front, Top, and Side View Views other than the Principal Views are called Auxiliary Views 5Pick the views which will help in describing the object with highest clarity.Explain what is an auxiliary view. Explain that they are drawn to show specific features that are not clear in the Principal views.

8AU 2005

8The Idea is to have them take an object from the table.

Declare front. FRONT View is the MOST DESCRIPTIVE VIEW OF THE OBJECT. The view that gives MORE INFORMATION ABOUT THE OBJECT.

Rotate 90 degrees up to get top view.

Rotate Back.

Rotate 90 degrees clockwise to get right side.

This give three principal views commonly used.

Methods of Drawing Orthographic ProjectionsFirst Angle Projections MethodHere views are drawn by placing object in 1st Quadrant( Fv above X-y, Tv below X-y )Third Angle Projections MethodHere views are drawn by placing object in 3rd Quadrant. ( Tv above X-y, Fv below X-y ) FVTVXYXYGLTVFVThird Angle Projection Associated with English units

First Angle Projection Associated with SI units First Versus Third Angle Projection

ANSI Symbol

16AU 2005Conventional Orthographic ViewsHeightDepthWidthFront ViewTop ViewRight Side View16Note that the views are placed and aligned in the manner shown in the diagram. Remind the students that they have to follow the above convention for all their home work problems and exam problems.

It is very important to maintain the alignment and correct placement relative to each other.

Means line for top (and bottom) is straight across for both front view and right side view for example.

Same thing between front and top for sides.

Note : The following can be seen from the slide:Top View and front view have the same widthFront View and Right / Left side view have the same height.The depth of Top view is same as the width of right/ left side view.

17AU 2005Step 1 Lightly Block Three Views

Use very light lines for drawing in the construction lines17Instructor:Construction lines are to be drawn lightly, gray vs. black, so that they will not reproduce on a Xerox machine and therefore do not have to be erased.

xyFRONT VIEWTOP VIEWL.H.SIDE VIEWFOR F.V.FOR S.V.FOR T.V.PICTORIAL PRESENTATION IS GIVENDRAW THREE VIEWS OF THIS OBJECTBY FIRST ANGLE PROJECTION METHODORTHOGRAPHIC PROJECTIONSF.V.S.V.

FOR F.V.FOR S.V.FOR T.V.S.V.F.V.

XYFRONT VIEWTOP VIEWL.H.SIDE VIEWORTHOGRAPHIC PROJECTIONS

PICTORIAL PRESENTATION IS GIVENDRAW THREE VIEWS OF THIS OBJECTBY FIRST ANGLE PROJECTION METHOD

FOR F.V.FOR S.V.FOR T.V.

F.V.S.V.ORTHOGRAPHIC PROJECTIONSXYFRONT VIEWTOP VIEWL.H.SIDE VIEW

PICTORIAL PRESENTATION IS GIVENDRAW THREE VIEWS OF THIS OBJECTBY FIRST ANGLE PROJECTION METHOD

S.V.F.V.FOR T.V.FOR F.V.FOR S.V.ORTHOGRAPHIC PROJECTIONS

FRONT VIEWTOP VIEWL.H.SIDE VIEWXYPICTORIAL PRESENTATION IS GIVENDRAW THREE VIEWS OF THIS OBJECTBY FIRST ANGLE PROJECTION METHOD

S.V.F.V.FOR T.V.FOR F.V.FOR S.V.ORTHOGRAPHIC PROJECTIONS

FRONT VIEWTOP VIEWL.H.SIDE VIEWXYPICTORIAL PRESENTATION IS GIVENDRAW THREE VIEWS OF THIS OBJECTBY FIRST ANGLE PROJECTION METHOD

FOR T.V.FOR S.V.FOR F.V.PICTORIAL PRESENTATION IS GIVENDRAW THREE VIEWS OF THIS OBJECTBY FIRST ANGLE PROJECTION METHODORTHOGRAPHIC PROJECTIONSFRONT VIEWTOP VIEWL.H.SIDE VIEWXY450XFVY3040TV30 D404015OFOR T.V.FOR F.V.PICTORIAL PRESENTATION IS GIVENDRAW FV AND TV OF THIS OBJECTBY FIRST ANGLE PROJECTION METHODORTHOGRAPHIC PROJECTIONSO20 D30 D60 DTV1030501035FVXYRECT.SLOTFOR T.V.FOR F.V.PICTORIAL PRESENTATION IS GIVENDRAW FV AND TV OF THIS OBJECTBY FIRST ANGLE PROJECTION METHODORTHOGRAPHIC PROJECTIONSTOP VIEWHIDDEN LINESHidden lines are used to represent surfaces that are not directly visible in an orthographic view.

SLANTED SURFACESSlanted surfaces are surfaces that are not parallel to either the horizontal or vertical axis.

PROJECTION BETWEEN VIEWS

COMPOUND LINESA compound line is formed when two slanted surfacesintersect. The true length of a compound line is not shown in the front, top, or side views.

OBLIQUE SURFACESOblique surfaces are surfaces that do not appear correctly shaped in the front, top, or side views

ROUNDED SURFACESRounded surfaces are surfaces that have constant radii,such as arcs or circles. Surfaces that do not have constantradii are classified as irregular surfaces

CASTINGSCasting is one of the oldest manufacturing processes. Metal is heated to liquid form, then poured into molds and allowed to cool. The resulting shapes usually include many rounded edges and surface tangencies