Instrumental Drawing Lecture Notes PDF

Typical Drawing Instruments (A Design is as good as its instruments) Conventional Drafting Tools Drawing Table Available in a variety of styles and sizes. Most are adjustable up and down, and can tilt to almost any angle from vertical 90° to horizontal. The drawing surface must be clean, flat, s...

Typical Drawing Instruments (A Design is as good as its instruments) Conventional Drafting Tools Drawing Table Available in a variety of styles and sizes. Most are adjustable up and down, and can tilt to almost any angle from vertical 90° to horizontal. The drawing surface must be clean, flat, smooth, and large enough to accommodate the drawing and some drafting equipment. If a T-square is to be used, at least one edge on the board must be absolutely true. Most quality boards have a metal edge to ensure against warping and to hold the T- square securely T-Square It provides a parallel straight edge for the beginning drawing drafter. It is composed of two parts: the head and the blade. The two parts are fastened together at an exact right angle. The blade must be straight and free of any necks and imperfections. Used to draw horizontal lines on the drawing sheet. Used to draw vertical lines and slanted lines with the help of additional equipment basically 45° and 60° triangles. Draw lines only against the upper edge of the blade. Make sure the head is held against the left edge of the drawing board to guarantee parallel lines. Use a T-square to align the drawing paper to the drawing board, and to draw parallel horizontal lines on the paper. Drafting Machine The standard drafting machine combines the functions of a parallel ruler, protractor, scales, and triangles. Various drafting operations requiring straight and parallel lines may be performed advantageously with a drafting machine. The majority of drafting machines are constructed so that the protractor head may be moved over the surface of a drafting table without change in orientation by means of a parallel- motion linkage. A drafting machine is a device that attaches to the drafting table and replaces the T- square, triangles and protractors. They increase the accuracy and greatly reduce drafting time. Most drafting machines have a protractor and a Vernier which permits reading to 5 minutes of an arc. Bow Compass A compass is used mainly to draw circles and circular curves of relatively short radius. The large pivot joint compass is satisfactory for drawing circles of 25 mm to about 300 mm in diameter without an extension bar. The pivot joint provides enough friction to hold the legs of the compass in a set position. One of the legs is equipped with a setscrew for mounting either a pen or a pencil attachment on the compass. The metal point extends slightly more than the lead to compensate for the distance the point penetrates the paper. Extension Bars Extension bars is available for large bow compass to draw large diameter circles. Divider Dividers are similar to compasses, except that both legs are provided with needle points. As with compasses, dividers are available in large and small sizes, and in pivot joint, and bow types. Pivot joint dividers are used for measurements of approximately 20 mm or more. For measurements of less than 20 mm, bow dividers should be used. Dividers are used to transfer measurements. To step off a series of equal distances, and to divide lines into a number of equal parts A divider is similar to a compass, except that it has a metal point on each leg. It is used to lay off distances and to transfer measurements. Triangles (Set Square) Triangles are used in combination with the T square or straightedge to draw vertical and inclined lines. They are usually made of transparent plastic, which allows you to see your work underneath the triangles. Two standard triangles are used by the drafters. One is the 30-60-degree triangle. The other is the 45-degree triangle. When laying out lines, triangles are placed firmly against the upper edge of the T-square. Pencils are placed against the left edge of the triangle, and lines drawn upwards, away from the edge. Parallel angular lines are made by moving the triangle to the right after each new line has been drawn. Triangles are used in combination with the T square or straightedge to draw vertical and inclined lines. They are usually made of transparent plastic, which allows you to see your work underneath the triangles. Two standard triangles are used by the drafters. One is the 30-60-degree triangle. The other is the 45-degree triangle. When laying out lines, triangles are placed firmly against the upper edge of the T-square. Pencils are placed against the left edge of the triangle, and lines drawn upwards, away from the edge. Parallel angular lines are made by moving the triangle to the right after each new line has been drawn. To test the straightness of a triangle, place it against the T square and draw a vertical line, then reverse the triangle and draw another line along the triangle is straight, the two lines will coincide; if they don’t coincide, the error is half the resulting space Drawing Templates Circle Template Ellipse Template Nuts, Bolt & Screw Screw Heads Template A template is a thin, flat piece of plastic containing various cutout shapes. It is designed to increase the speed and accuracy of the drafter. Templates are available for drawing circles, ellipses, plumbing fixtures, bolts, nuts, screw threads, electronic symbols, springs, gears and much more. A template should be used whenever possible to increase the accuracy and the speed. French Curves and Flex Curves French curves are thin plastic tools that come in assortment of curved surfaces. They are used to produce curved lines that cannot be made by a compass. Most common French curves are actually segments of ellipses, parabolas and hyperbolas. Adjustable curves may also be used to create a smooth curve between a set of points. Protractor Protractors are used for measuring and laying off angles other than those that may be drawn with the triangle or a combination of triangles. Like the triangle, most protractors are made of transparent plastic. They are either circular or semicircular in shape. To use a protractor, place the center point on the corner point of the angle. Align the base of the protractor along one side of the angle. The degrees are read along the semicircular edge. Erasing Shield An erasing shield restricts the erasing area so that the correctly drawn lines will not be disturbed during the erasing procedure. It is made from a thin flat piece of metal with variously sized cutouts. The shield is used by placing it over the line to be erased and erasing through the cutout. Drawing Tape Used for fastening drawing paper on the drawing table. Metric Scales Inches Scale Wooden Pencil Grades Pen Sizes and Line Weights Line weights are a vital part of conventional technical graphics language. They are embodied to the extent of being defined in national and international standards. In manual drafting, different pen sizes allow the drafter to give different line weights to the lines in the drawing. Line types and line weights allow drawings to communicate information that would otherwise be very difficult to convey. For example: Hidden outlines Paths of motion Planes of symmetry Fictitious outlines such as major and minor diameters of screw threads Dimensions and projections Materials (hatching) Centers and imaginary intersections To make your drawings easy to read, make the contrast between thick and thin lines distinct. Thick lines (0.6 mm) should be twice the width of thin lines (0.3 mm) Alphabet of Lines Triangle Wheel Most inclined lines are drawn at standard angles using the 45º triangle and the 30º x 60º triangle. In addition to drawing angles of 90º, 45º, 30º, and 60º, triangles can be combined to draw angles of 15º increments. References: Giesecke F.E., Mitchell, A., Spencer, H.C., Hill,I.L., Dygdon, J.T., Novak, J.E., Lockhart, S.(2009). Technical drawing (13th Edition). Philippines: Pearson Education South Asia Giesecke F.E., Mitchell, A., Spencer, H.C., Hill,I.L., Dygdon, J.T.(1985). Technical drawing (7th Edition). New York: Macmillan Publishing Co. National Building Code of the Philippines Fundamentals of Engineering drawing, by Waren J. Luzadder http://tolerancing.net/engineering-drawing/engineering-drawing.html https://www.indovance.com/knowledge-center/projection-methods-used-in-mechanical- drawing/