Engineering Graphics 2018-19-I Lecture 6 TA101A Engineering Graphics 2018-19-I By Dr. Mukesh Sharma Professor DEPARTMENT OF CIVIL ENGINEERING INDIAN INSTITUTE OF TECHNOLOGY KANPUR KANPUR-208016, INDIA

PRACTICE

PRACTICE

3-D to Orthographic Projection Orthographic Projection – 3D Axonometric – Isometric Oblique Perspective Why do we need 3-D Pictorial Drawings?

Can get Infinite 3-d views – needs uniformity and standardization Rotated about vertical axis (two faces seen) Rotated about vertical & profile Axes (three faces seen) Parallel to Picture plane (only one face seen) Can get Infinite 3-d views – needs uniformity and standardization

First Position – one face seen R,U T First Position – one face seen R,S T U S R,U T R U Rotate about Vertical axis by 450 Two faces seen Then Rotate about profile axis by 350 (three faces seen) S R U T Three mutually perpendicular Edges, SR, RU and RT now make equal angle of 120o with each other and are called ISOMETRIC AXES Projections are still orthographic What these rotations have done? SR, RU, RT all foreshortened but by equal lengths

Schematic presentation of concept

Quiz: How much AB is foreshortened? A Isometric Axes B 30o 30o One Can draw isometric Figure with the help of Isometric box Two types : (i) Isometric Projection – Take lines as foreshortened (ii) Isometric drawing - Disregard foreshortening take actual length

Isometric projection: foreshortened (81/100) A B Isometric projection: foreshortened (81/100) Isometric drawing: No foreshortening (100/100) No difference in shape - Isometric drawing larger in Linear proportion of 1.23:1. Most common form is to use isometric drawing

Important All lines parallel to isometric axes – Isometric lines All isometric lines are foreshortened equally (81/100) All other non-isometric lines may or may not foreshorten Foreshortening ratio of such lines may vary disproportionately Projections of parallel lines are parallel. All measurements can only be marked on isometric lines

ISOMETRIC SCALE 4 3 Regular Scale 2 450 4 1 3 300 Isometric Scale 2 1 Make Isometric scale : foreshortened to 81/100 to Be used in Isometric projection

Decide width and depth directions – height direction is fixed. 12 20 12 20 10 B 10 A C Decide width and depth directions – height direction is fixed.

D C B A D C B A Boxing Method

Top Now start drawing Isometric Front Right Side

Now erase the hidden lines Front Top Right Side 300 300 Identify hidden lines Now erase the hidden lines

Front Top Right Side Now erase hidden portion of ellipse

Front Top Right Side Isometric

Top Now start drawing Isometric Front Right Side

Draw base as in previous isometric Now draw the additional surface Front Top Right Side Smoothly join both ellipses Identify hidden lines and erase

Front Top Right Side Isometric