Technical Sketching PDF

PRODUCTION DRAWING BET 141 PREPARED BY: ELLA MAY R. BAGOS,MT PRODUCTION DRAWING Production or working drawings are complete sets of drawings that have detailed description of the manufacturing and assembly of designed products. The main purpose of production drawings is to define the size, shape,...

PRODUCTION DRAWING BET 141 PREPARED BY: ELLA MAY R. BAGOS,MT PRODUCTION DRAWING Production or working drawings are complete sets of drawings that have detailed description of the manufacturing and assembly of designed products. The main purpose of production drawings is to define the size, shape, location and production of the component. Machine operators, production line workers and supervisors all use production drawings. Front View Side View Isometric View  Visualization Communication Documentation Technical Sketching 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. Technique of Lines The chief difference between a mechanical drawing and a freehand sketch lies in the technique of the lines. A good mechanical 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. Technique of Lines If your line looks like this, you may be gripping your pencil too tightly or trying too hard to imitate mechanical lines Slight wiggles are “OK” as long as the line continues on a straight path Occasional very slight gaps are fine and make it easier to draw straight. Technique of Lines Method for Sketching Circles  Proportions The most important rule in freehand sketching is to keep the sketch in proportion. No matter bow brilliant the technique or how well the small details are drawn, if the proportions particularly the large over-all proportions are bod, 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  Proportions 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 the figure. 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 multi view projection. Isometric Sketching The steps in sketching isometric are: l. Sketch the enclosing box lightly, closely resembling the tilted object as shown in the figure. 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. II. Block in the recess and the projecting block. III. Dim all construction lines with soft eraser and heavy in all final lines. Isometric Ellipses shown in the figure below 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 as shown in the figure. Hold the object as shown. l. Block in the front face of the Bearing, as if you were sketching a front view. ll. 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. lll. Dim all construction lines with soft eraser and heavy in the final lines. Perspective Sketching l. 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 ll. Sketch the receding lines toward VP III. Estimate the depth to look well, and sketch in the back portion of the object. Note that the back circle and are will be slightly smaller than the front circle and arc. IV. Dim all construction with a soft eraser, and heavy in all final lines.