ME 111: Engineering DrawingLecture 5

12-08-2011Orthographic projection and

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Orthographic projection and Projection of Points

Indian Institute of Technology GuwahatiGuwahati – 781039

Orthographic ProjectionOrthographic Projection� A parallel projection technique in which the plane of

projection is perpendicular to the parallel line of sight.

� Orthographic projection technique can produce either pictorial drawings that show all three dimensions of an object in one view, or multi-views that show only two dimensions of an object in a single view.dimensions of an object in a single view.

MultiMulti--view Projectionview ProjectionIn an orthographic projection, the object is oriented in sucha way that only two of its dimensions are shown. Thedimensions obtained are the true dimensions of the object

Frontal plane of projectionFrontal plane of projection

Frontal plane of projection is the plane onto which the Front View (FV) of the multi-view drawing is projected.Front view of an object shows the width and height dimensions.

Horizontal plane of projectionHorizontal plane of projectionHorizontal plane of projection is the plane ontowhich the Top View of the multi-view drawing isprojected.Top view of an object shows the width and depthdimensions.

Dr P. S. RobiIIT Guwahati

Profile plane of projectionProfile plane of projectionIn multi-view drawings, the right side view is the standardside view used. The right side view of an object shows thedepth and the height dimensions. The right side view isprojected onto the profile plane of projection, which is aplane that is parallel to the right side of the object.

Orientation of views from projection Orientation of views from projection planesplanes

Top view is alwayspositioned andaligned with thefront view, and sidefront view, and sideview is alwayspositioned to theside of and alignedwith the front view.

Six Principal viewsSix Principal views• The plane of projection can be oriented to produce an

infinite number of views of an object. However, someviews are more important than others.

• These principal views are six mutually perpendicularviews that are produced by six mutually perpendicularplanes of projection.planes of projection.

• Imagine suspending an object in a glass box with majorsurfaces of the object positioned so that they areparallel to the sides of the box, six sides of the boxbecome projection planes, showing the six views –front, top, left, right, bottom and rear.

Six Principal ViewsSix Principal ViewsObject issuspended in aglass boxproducing sixprincipal views:each view iseach view isperpendicular toand aligned withthe adjacentviews.

Unfolding the glassbox to produce six-view drawing

• Top, front and bottomviews are all alignedvertically and sharethe same widthdimension.

• Rear, left side, frontand right side viewsare all alignedhorizontally and sharethe same heightdimension.

Conventional view placementThe three-view multiviewdrawing is the standardused in engineering andtechnology, because manytimes the other threeprincipal views are mirrorimages and do not add tothe knowledge about thethe knowledge about theobject.

The standard views used ina three-view drawing arethe top, front and the rightside views

The width dimensions arealigned between the frontand top views, usingusing verticalverticalprojectionprojection lineslines..

The height dimensions arealigned between the frontand the profile views, usinghorizontal projection lines.

Because of the relativepositioning of the threeviews, the depth dimensioncannot be aligned usingprojection lines. Instead, thedepth dimension ismeasured in either the top orright side view.

The principalprojectionplanes andquadrantsused tocreate first-and third-angleprojectiondrawings

Orthographic projection andProjection of points

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Indian Institute of Technology GuwahatiGuwahati – 781039

ExampleTV

X1

1. Visible2. Hidden3. Center

FV RHSV

X Y

Y1

Conventions

Convention

• Projectors and the lines of the intersection of planesof projections are shown as thin lines.

• Visible lines take precedence over all other lines

• Hidden lines take precedence over center lines

Precedence of Lines

0.70 mm

• Hidden lines take precedence over center lines

• Center lines have lowest precedence0.35 mm

0.35 mm

Example: Application of Precedence

Intersecting Lines in Orthographic Projections

Solid Line Intersections

Dashed Line Special Case IntersectionsDashed Line Special Case Intersections

Intersection of hidden line

Projection of Points(Orthographic)

P

A POINTDefine its position with respect to the coordinates.

With respect to the VP, HP, & PP

PP

Direction of rotation of the HP

Convention

• Top views are represented by only small letters eg. a.

• Their front views are conventionally represented bysmall letters with dashes eg. a�small letters with dashes eg. a�

• Profile or side views are represented by small letterswith double dashes eg. a��

Convention

• The line ofintersection of HP andVP is denoted as XY.

• The line ofintersection of VP andPP is denoted as X1Y1

Convention

• Projectors and the lines of the intersection of planesof projections are shown as thin lines.

Point in the First quadrantPoint P is 40 mm in front of VP, 50 mm above HP, 30 mm in front of left profile plane (PP)

Point in the First quadrant

Point in the First quadrant

Point in the First quadrant

Procedure

• Draw a thin horizontalline, XY, to representthe line of intersectionof HP and VP.of HP and VP.

• Draw X1Y1 line torepresent the line ofintersection of VP andPP.

• Draw the Top View (p).• Draw the projector line• Draw the Front View

(p�)

Y1

Point in the First quadrant

Procedure

• To project the rightview on the left PP,draw a horizontalprojector through p tointersect the 45 degreeintersect the 45 degreeline at m.

• through m draw avertical projector tointersect the horizontalprojector drawnthrough p� at p��.

• p�� is the right view ofpoint P

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