Sketching - LESSON-1-PDF

## SKETCHING ### Importance The importance of freehand drawing or sketching in engineering and design cannot be over-estimated. To the person who possesses a complete knowledge of drawing as a language, the ability to execute quick, accurate and clear sketches of ideas constitutes a valuable means...

## SKETCHING ### Importance The importance of freehand drawing or sketching in engineering and design cannot be over-estimated. To the person who possesses a complete knowledge of drawing as a language, the ability to execute quick, accurate and clear sketches of ideas constitutes a valuable means of expression. Since most original ideas find their first expression through the medium of a freehand sketch, it is therefore an indispensable means of amplifying and clarifying, as well as recording verbal expressions. Freehand sketches are of great assistance to the designer in organizing his thoughts and recording his ideas. They are an effective and economical means of formulating various solutions to a given problem so that a choice can be made between them on the onset. Often much time can be lost if the designer starts his scaled layout before adequate preliminary study with the aid of sketches. The term freehand sketch is too often understood to mean a crude or sloppy freehand drawing in which no particular effort has been exerted. On the contrary, a freehand sketch should be made with care and with attention to correct line widths. ### Sketching Materials Freehand sketching requires only paper, pencil and eraser which are items that anyone must have for ready use. For excellent sketching, one can use a plain white paper called sketch pad which is heavier than bond paper and may be purchased at low cost from local bookstore or school supply establishment. Beginning sketchers especially those who cannot sketch reasonably well without guide lines can use cross-section paper or graphing paper which are available in sheets or pads. These papers are also conveniently used for sketching to scale since values can be assigned to the squares and the squares counted to secure proportional distances. ### Sharpening Pencils Use a soft pencil, such as HB or F and sharpen it to a conical point for center lines, extension lines and dimension lines. For visible lines, hidden lines and cutting-plane lines, round off the point slightly to produce the desired thickness of line as illustrated in Fig. 1.1. Except for the construction lines which are drawn very light, all lines should be made dark. Note: Soft pencils, such as HB or F, should be used for freehand sketching and for carefully made sketches, soft erasers are recommended for use. Sharpen it to a conical point as shown in Fig. 1.1. Use sharp point for center lines, dimension lines and extension lines. For visible lines, hidden lines and cutting-plane lines, round off the point slightly to produce the desired thickness of line and make all lines dark except for construction lines which should be drawn very light. ### Technique of Lines The chief difference between a mechanical drawing and a freehand sketch, Fig. 1.2 lies in the technique of the lines. A good instrumental line is drawn rigidly straight and exactly uniform while that of freehand line is drawn with freedom and variety. The freehand construction line is a very light rough line wherein some of the strokes may overlap and all other lines should be dark and clean-cut. Ends of all dashes are accented and sharp contrasts between line thicknesses are maintained. All visible lines are drawn heavy so the outline will stand out clearly and make hidden lines, center lines, dimension lines and extension lines thin. ### Straight Lines Since almost all lines on the average sketch are straight lines, it is necessary to learn on how to make them well. Figures 1.3 to 1.6 are pictorial demonstrations of drawing straight lines. ### Circles and Arcs Small circles and arcs can be easily sketched in one or two strokes as in stroking the circular portions of letters. The following are the preferred methods as presented in Figures 1.7 and 1.8. ### Ellipses Ellipses are circles viewed obliquely. With a little practice, you can learn to sketch small ellipses with a free hand movement and large ellipses with a free arm movement. See Fig. 1.9 for sketching ellipses. ### Proportions The most important rule in freehand sketching is to keep the sketch in proportion. No matter how brilliant the technique or how well the small details are drawn, if the proportions particularly the large over-all proportions are bad, the sketch will be bad. In sketching from an actual object, various distances can be easily compared on the object by using your pencil to compare measurements as shown in Fig. 2.0. It should be remembered that while doing this, you should always hold your pencil at arm's length and stay at your position until you are through comparing measurements. The length sighted can then be compared in similar manner with any other dimension of the object. In establishing proportions, especially for irregular shapes, the blocking-in method is recommended. The steps in blocking-in and completing the sketch of a Shaft Hanger are shown in Fig. 2.1. As always, first give attention to the main proportions, next to the general sizes and direction of flow of curved shapes and finally to the snappy lines of the completed sketch. ### Pictorial Sketching The foregoing are simple methods of preparing pictorial sketches. Although prepared in freehand, they must be carefully sketched applying the rules in estimating dimensions and in establishing proportions. Let us now examine several methods of preparing pictorial sketches that will be of great assistance in learning the principles of multiview projection. #### Isometric Sketching The steps in sketching isometric are: 1. Sketch the enclosing box lightly, closely resembling the tilted object as shown in Fig. 2.2. The front center of the box will appear vertical and the two receding bottom edges and those parallel to them will appear at about 30° with horizontal. 2. Block in the recess and the projecting block. 3. Dim all construction lines with soft eraser and heavy in all final lines. #### Isometric Ellipses Shown in Figure 2.3 are objects having cylindrical or conical shapes and are placed in the isometric position; hence, circles viewed at an angle will appear as ellipses. ### Oblique Sketching Another simple method for sketching pictorially is oblique sketching, Fig. 2.4. Hold the object as shown. 1. Block in the front face of the Bearing, as if you were sketching a front view. 2. Sketch receding lines parallel to each other and at any convenient angle, normally at 30° or 45° approximately with horizontal. To obtain a more natural appearance, cut the estimated depth to about three-quarters or one-half size approximately. 3. Dim all construction lines with soft eraser and heavy in the final lines. ### Perspective Sketching The Bearing sketched in oblique in Fig. 2.4 can easily be drawn in one-point perspective (one vanishing point), as shown in Fig. 2.5. 1. Sketch the true front face of the object, the same as in oblique sketching. Select the vanishing point (VP) for the receding lines. In most cases, it is desirable to place VP above and to the right of the drawing, as shown. 2. Sketch the receding lines toward VP. 3. Estimate the depth to look well, and sketch in the back portion of the object. Note that the back circle and arc will be slightly smaller than the front circle and arc. 4. Dim all construction with a soft eraser, and heavy in all final lines. ### Suggested Sketching Exercises There are two images depicting exercises to be completed, one for lines and one for arcs and circles. ### Pictorial Sketching For Plate No._ Pictorial Sketching, Lay-out sheet, use the trims of the drawing as the border of your drawing paper, sketch the given objects as shown strictly observing the rules on proportions, isometric sketching and sketching ellipses. Note: omit instructional notes and construction lines. ### Self-Test 1. What is the main reason for preparing sketches? 2. What is the chief difference of a mechanical line from a freehand line? 3. When do we use ellipses? 4. Why is establishing proportion important in freehand sketching?