Engineering Graphics, Class 4Sketching and line techniques

Mohammad I. KilaniMechanical Engineering Department

University of Jordan

Sketching and Line Techniques

Even in the world of high technology and computer skills, sketching is still one of the most important skills for engineers and designers.Sketching is one of the first steps in communicating ideas for a design, and it is used in every step thereafter.It is common practice for designers to prepare sketches that are turned over to drafters for conversion to finished work drawings.Sketches consist of straight and curved lines. With practice, you can become skilled in creating neat, sharp and clear sketches involving all types of lines introduced.

Sketching Lines

The lines used in creating sketches closely correspond to those used in creating technical drawings, except, of course, that they are not as sharp and crisp.The basic line types used in making sketches are: visible lines, hidden lines, center lines, dimension lines, sectioning lines, extension lines and cutting plane lines. These lines represent the various lines available for creating sketches.The character of each line should be closely monitored when making sketches.

Types of Sketches: Orthographic and axonometric sketches

There are four types of sketches: orthographic, axonometric, oblique, and perspective.Orthographic sketching relates to flat impression of an object showing no depth. Six principal views of an object may be incorporated in an orthographic sketch: top, front, bottom, back, right side and left side. The views selected for use in a sketch depend on the nature of the subject and the judgment of the sketcher.Axonometric sketching may be isometric, dimetric or trimetric. The type most frequently used is isometric, in which length and width lines recede 30o to the horizontal and height lines are vertical

Types of Sketches: Oblique and perspective sketches

Oblique sketching involves a combination of a flat orthographic front surface, with depth lines receding at a selected angle, usually 45o.Perspective sketching involves creating a graphic image of an object as seen by a human observer. Consequently, depth lines must recede to a hypothetical vanishing point, or points.

Sketching Materials and Graph Paper

An advantage of sketching is that it requires very few material aids. Whereas a drafter must have a complete collection of tools, sketching requires only a pencil and a piece of paper.Sketching done in a formal working environment requires three basic materials: pencil, media (paper of graph paper), and an eraser.Graph paper simplifies the sketching process considerably, and should be used freely.

Sketching Techniques: Sketching Rules

Hold the pencil firmly, but not so tightly, as tension creates hand fatigue.Grip the pencil approximately 25 mm to 40 mm up from the point.Maintain a comfortable angle between the pencil and the sketching strokes.Draw horizontal lines from left to right using short, slightly overlapped strokes

Sketching Techniques: Sketching Rules

Draw vertical lines from top to bottom using short, slightly overlapped strokes, and using finger and wrist movement.Inclined lines may be made to conform in direction to horizontal or vertical lines by Shifting position with respect to the paper or, by turning the paper slightly

Sketching Techniques: Sketching Straight Lines

Making straight lines on graph paper is a simple process of guiding the pencil using the existing lines.If graph paper is not available, pencil dots can be positioned to plot the path of the line.The sketcher enters a series of pencil dots on the paper which provide a basic outline as to the shape of the object.Using a series of short, slightly overlapped strokes, the pencil dots are connected. This technique is also used for curved lines.

Sketching Circles

Sketch lightly the enclosing square of the circleMark the mid points of the sides of the enclosing squareDraw light arcs tangent to the sides of the squareHeavy in the final circle

Sketching Ellipses

Sketch lightly the enclosing rectangle of the ellipseMark the mid points of the sides of the enclosing rectangleDraw light arcs tangent to the sides of the ellipseHeavy in the final ellipse

Proportion in Sketching

Sketches are not done to scale, but it is important that they bemade proportionately accurate.In sketching, use graph paper whenever possible.

Sketching

Sketches are not done to scale, but it is important that they be made proportionately accurate.In sketching, use graph paper whenever possible. Examine the position to be sketched mentally and break it into its component parts.Beginning with the largest component, estimate the proportion of the of length to width, and layout a box enclosing that component.Use construction line squares and rectangles to block in irregularly shaped components.Repeat the two previous steps until the entire object is finished.

Isometric Sketching

Isometric sketching is one of several simple methods of preparing pictorial sketches. This methods helps in learning multiviewprojection.To make an isometric sketch from an actual object, hold the object in your hand, tilt it toward you such that the front corner appears verticalThe two receding bottom edges and those parallel to them, respectively, will appear at about 30o

with horizontal

Isometric Sketching

Sketch the enclosing box lightly, making AB vertical and AC and AD approximately 30o with horizontal. Lines AB, AC, and AD are called the isometric axesMake lines AB, AC, and AD approximately proportional in length to the actual corresponding edges on the objectSketch the remaining lines parallel, respectively, to these three linesBlock in the recess and the projecting blockLighten all the construction lines with a soft eraser and heavy in all final lines.

Orthographic Sketching

Orthographic sketching may involve sketching any combination of the six principal views of the subject.The appropriate views are those that show the most detail with the fewest hidden lines.A good rule is to select the view which would give the most of the information about the subject,To ensure that the sketched views align, the entire sketch should be blocked in before adding details.The details can be added one view at a time.

Isometric Sketching on Isometric Paper

Using isometric paper, individual planes or faces may be constructed to build up a pictorial visualization from a given viewsSketch the isometric of the enclosing box, counting off the isometric grid spaces to equal the corresponding squares on the given viewsSketch surface A. Sketch additional surfaces B, and C and the small ellipseSketch additional surfaces E, F, G, and H to complete the sketch