LECTURE 2: SKETCHING ENS 207 ENGINEERING GRAPHICS 1

LECTURE 2: SKETCHING

ENS 207 ENGINEERING GRAPHICS

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Freehand Sketching

Freehand sketches are a helpful way to organize your thoughts and record ideas. They provide a quick, low-cost way to explore various solutions to design problems so that the best choices canbe made.

TECHNIQUE OF LINESThe chief difference between a drawing and a freehand sketch lies in the character or technique of the lines.

line patterns

A good freehand line is not expected to be as rigidly straight or exactly uniform. A good freehand line shows freedom and variety, whereas a line drawn using CAD or instruments should be exact.

LineweightsEven in freehand drawings, thick lines should be twice the width of thin lines.Thicknesses do not have to be exact, but there should be an obvious difference between thick and thin lines. Because visible lines and cutting-plane lines are the two thick line patterns, other lines should be distinctlythinner in comparison.

To draw thick and thin lines freehand,you might like to keep two pencilshandy, one that is razor sharp for thinlines and another that is dulled, tocreate thicker lines. As the sharp pointbecomes dulled, switch it with thedull pencil, and sharpen the other,so that there is always one sharpand one dulled point ready to use.

FREEHAND LINESThe main difference between an instrument or CAD drawing and a freehand sketch is in the appearance of the lines. A good freehand line is not expected to be precisely straight or exactly uniform, as is a CAD or instrument-drawn line. Freehand lines show freedom and variety.

Freehand construction lines are very light, rough lines. All other lines should be dark and clean.

Edges and Vertices

EdgesAn edge of the solid is formed where two surfaces intersect. Edges are represented in drawings by visible or hidden lines.

VerticesA vertex (plural, vertices) of a solid is formed where three or more surfaces intersect..

PointsA point is used to represent a location in space but has no width, height, or depth.

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For Example:

1. Visible

2. Hidden

3. Center

Horizontal line Vertical line

Small Circle

Method 1 : Starting with a square

1. Lightly sketching the square and marking the mid-points.

2. Draw light diagonals and mark the estimated radius.

3. Draw the circle through the eight points.

Step 1 Step 2 Step 3

ArcMethod 1 : Starting with a square

Method 2 : Starting with a center line

Example

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PROPORTIONSSketches should be proportional. A square should look like a square, and a rectangle like a rectangle. Graph paper is very helpful in sketching proportionally, but it is still sometimes difficult to be accurate even with graph paper.

CURVES

Curved shapes are best sketched by first defining points along the curve, then lightly sketching the curve between the points.

Circles and EllipseAn ellipse can be sketched by first sketching a perpendicular axis, then locating four marks on the centerlines that are approximately equal to major and minor axis distances. Sketch a light curve, make any corrections necessary, anddarken in the elliptical shape.

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Introduction to Isometric Projection

• Isometric means equal measure• All planes are equally or proportionately shortened and tilted• All the major axes (X, Y, Z) are 120 degrees apart

CUBE

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Making an Isometric Sketch• Defining Axis

30o 30o

60o60o

Isometric Axis

Three planesThe three planes of an isometric axis are defined as theleft, right, and top planes, respectively

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DepthWidth

Height

Isometric Axis Convention

Making an Isometric Sketch• Axis Convention

Front view

Choose the longest dimension to be the width (or the depth) for optical

stability

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Object for Practice

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Blocking in the ObjectBegin with Front Face

Front Face

Height

Width

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Blocking in the Object: Add Side Face

Height

Depth

Side Face

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Blocking in the Object: Add Top Face

Top Face

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Adding Detail Cut Outs – Part 1

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Adding Detail Cut Outs – Part 2

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Adding Detail Cut Outs – Part 3

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Darken Final Lines - Part 4

Note: All visible edges will be darkened

PLANNING YOUR DRAWING OR SKETCH

When laying out a drawing sheet, you willneed to consider:

• the size and scale of the object you will show

• the sheet size

• the measurement system (units) for the drawing

• the space necessary for standard notes and title block.