Technical Drafting

Technical Drafting

∗ The process of creating a technical drawing

BEFORE proceeding with the manufacturing of a

technical object.

∗ When drafting objects, care must be taken to draw

accurately and neatly.

∗ A RULER must be used at all times for all lines –

straight or curved.

∗ All lines should be drawn as a single line - do NOT

shade any line.

✗Shaded line✓Single line

Drawing Lines

∗ Lines on an engineering drawing signify more than just the geometry of the object and it is important that the appropriate line be is used.

Line Thickness

∗ For most engineering drawings you will require two thickness', a thick and thin line. The general recommendation are that thick lines are twice as thick as thin lines. ∗ A thick continuous line is used for visible edges and outlines.

∗ A thinner continuous line is used for leader lines, short centre lines, dimensions and projections.

Line Styles

∗ Other line styles used to clarify important features on drawings are:∗ Thin chain lines are a common feature on

engineering drawings used to indicate centre lines. Centre lines are used to identify the centre of a circle, cylindrical features, or a line of symmetry.

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Line Styles

∗ Dashed lines are used to show important hidden detail for example wall thickness and holes.

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Line Styles

Projections

∗ A projection is the representation of a 3D object on a 2D surface.

∗ Isometric Projections

∗ Multiview Projections

Isometric Projections∗ When an object is drawn so that the lines representing

its length, height, & depth form 120° angles on the paper.

∗ An isometric projection shows the object in PERSPECTIVE – it represents three dimensions of the object in a single view.

Isometric Projections

Drawing Isometric Projections

Multiview Projections

∗ Using basic lines, the drafter draws the different views of the object just as they appear from each side.

∗ Each view in a multiview projection is represented in two dimensions.

Glass Box Approach

Glass Box Approach

Glass Box Approach

Glass Box Approach

Glass Box Approach

Glass Box Approach

Multiview Projections

∗ Although a multiview projection can represent the object in its entirety, usually only the front, top and right-side views are illustrated.

∗ The great advantage a multiview projection has over an isometric projection is the ability to show greater detail without distortion.

∗ If in one of the views, details are hidden, you must indicate that using a dashed line

Multiview Projections

∗ Check out the following link for an instructive video on how to draw multiview projections:

∗ Multiview Projection #1

(http://www.wisc-online.com/Objects/ViewObject.aspx?ID=ENG19204)

Top View

Front View Right Side View

Top View

Front View

Right Side View

Hidden lines

Center line

Exploded View

∗ An exploded view drawing in which the various parts of the object are separated from one another. (Usually drawn to scale.)

∗ This type of drawing is often included in instruction leaflets describing steps for do-it-yourself assembly of an object. (ex: wheel barrow)

Engineering Drawings

∗ A general arrangement is a technical drawing showing the overall appearance of an object – NOT all the relevant information for manufacturing the parts of the object are represented. ∗ Multiview projections are suitable for this type of

drawing, because they contain many details of the object.

∗ However, a representation in an isometric projection is often added because it offers the advantage of showing the general shape of the object in a single view.