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

2 SheetCourse: Engineering Graphics 1504Memorial University of Newfoundland 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!

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

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

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

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

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

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

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

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

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

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

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

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

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

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

17 SheetCourse: Engineering Graphics 1504Memorial University of Newfoundland Class Assignment #3 l Sketch an isometric of example 2.6 in text (freehand) l Sketch an isometric of question #80 in Chapter 2 of the text (use instruments and scale to larger size)