Engineering Graphics 1504 Lecture 2 General Sketching Objectives

Engineering Graphics 1504 Lecture 2 – General Sketching Objectives l Lines l Arcs l Pictorial Types Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 1

Sketching Straight Lines • Lightly mark endpoints of line. • Lightly sketch from one endpoint to the other. • Use 1 to 2 inch strokes, keeping eye on the second endpoint. DON’T USE A STRAIGHT EDGE! Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 2

Sketching Circles and Arcs Diameter The “ 2/3” method 2/3 of center distance PLUS SIGN MARKS CENTER SKETCH SQUARE SKETCH ARCS FOR CIRCLE Course: Engineering Graphics 1504 Memorial University of Newfoundland SKETCH AND MARK DIAGONALS DARKEN CIRCLE Sheet 3

Pictorial Representation l l Illusion of three dimensions Shows more information Easier to visualize Often used to explore ideas, aid explanation, present information Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 4

Three Types of Pictorial Sketches perspective Course: Engineering Graphics 1504 isometric Memorial University of Newfoundland oblique Sheet 5

Perspective Drawings l l l Represents what the eye sees Railway tracks come together Vanishing points Do not show true size or lengths. Used to show “artist’s conception” Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 6

Isometric Drawings l l l Want to show more sides of the object in one view Rotate 45º about vertical axis through centre Two views sides shown in front view Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 7

Isometrics l l l Tip forward about the corner ‘x’ Top view now shows front, top, and side of cube Isometric if cube is ‘tipped’ so that sides are of equal length and make angle of 30º to the horizontal Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 8

Isometrics l l Isometric – equality of measure All sides in an isometric drawing are drawn to actual size (close to truth) Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 9

Isometrics l l l Any line parallel to an isometric axis is measured as true length Any line not parallel to an axis is not true length Diagonals on a real cube are of equal length – not the case here Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 10

Oblique Projection l l l Sometimes an isometric drawing may have features that are difficult or time consuming to represent (e. g. circle). If lines of sight through picture plane are at an angle other than 90º, get oblique projection Front view drawn to normal size, other views are drawn at some angle (typically 30º, 45º, 60º) Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 11

Oblique Projection l l Two common types of oblique projections are cavalier and cabinet Front view is full size in both types but scale on receding axis is different Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 12

Break Time l Take 5 minute break Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 13

Making an Isometric Drawing l l Construct isometric axes Block out space occupied by the shape Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 14

Making an Isometric Drawing l l Draw lines parallel to axes at key points No hidden lines are shown in a pictorial! Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 15

Sketching Circles in Isometric Drawings l l l A circle appears as an ellipse in isometric Locate centre by joining the corners and drawing diagonals Use same procedure as outlined for orthographic sketching Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 16

Class Assignment #3 l l Sketch an isometric of example 2. 6 in text (freehand) Sketch an isometric of question #80 in Chapter 2 of the text (use instruments and scale to larger size) Course: Engineering Graphics 1504 Memorial University of Newfoundland Sheet 17