Manual drafting, also known as hand drafting, describes traditional drafting practice using pencil or ink on a medium such as paper or polyester film, with the support of drafting instruments and equipment. This chapter also explains drawing scale, sheet size, and sheet format.
design and drafting
(CADD) has replaced manual drafting in most of the drafting industry.
As a result, some of the information in this chapter primarily serves as a historical reference. However, both manual drafting and CADD require that you understand the basics of drafting. Concepts such as scale, sheet size, and sheet format are critical and universal to manual drafting and CADD. Also, some companies use CADD but have manual drafting equipment available that you should be able to recognize and operate at a basic level.
EQUIPMENT AND SUPPLIES
Professional manual drafting requires appropriate drafting of equipment and supplies. If you work in a modern
environment, manual drafting tools such as compasses, dividers, triangles, templates, and scales have less importance. However, they are still valuable for sketching, taking measurements, and other related activities. You can purchase drafting supplies and equipment in a kit or buy items individually. Manual drafting equipment is available from many local and online vendors. Search the Internet or a phone book for keywords or headings such as drafting equipment and supplies, blueprinting, architect supplies, and artist supplies. Always purchase quality instruments for the best results. The following is a list of items generally needed for typical manual drafting:
• Drafting furniture.
• One 0.3 mm automatic drafting pencil with 4H, 2H, and H leads.
• One 0.5 mm automatic drafting pencil with 4H, 2H, H, and F leads.
• One 0.7 mm automatic drafting pencil with 2H, H, and F leads.
• One 0.9 mm automatic drafting pencil with H, F, and HB leads.
• Sandpaper sharpening pad.
• Erasers recommended for drafting with pencil on paper.
• Erasing shield.
• Dusting brush.
• 6 in. Bow compass.
• 8 in. 30–60 triangle.
• 8 in. 45 triangle.
• Circle template with small circles.
• Circle template with large circles.
• Irregular curve.
• Triangular architect's scale.
• Triangular civil engineer's scale.
• Triangular metric scale.
• Drafting tape.
• Lettering guide (optional).
• Arrowhead template (optional).
OB体育ob体育官网 PENCILS AND LEADS
Automatic pencils are standard for manual drafting, sketching, and other office uses. The term automatic pencil refers to a pencil with a lead chamber that advances the lead from the chamber to the writing tip by the push of a button or tab when a new piece of lead needed. Automatic pencils hold leads of one width, so you do not need to sharpen the lead. The pencils are available in several different lead sizes.
Drafters typically have several automatic pencils. Each pencil has a different grade of lead hardness and is appropriate for a
specific technique. This reduces the need to change leads constantly. Some drafters use a light blue lead for layout work. If your primary work is CADD, a combination of 0.5-, 0.7-, and 0.9 mm pencils and leads is good for sketching and related activities.
Lead grades of 2H and H are good in your automatic pencil for typical daily office use. The leads you select for line work and lettering depend on the amount of pressure you apply and other technique factors. Experiment until you identify the leads that give the best line quality. Leads commonly used for thick lines range from 2H to F, whereas leads for thin lines range from 4H to H, depending on individual preference.
Construction lines for layout and guidelines are very lightly drawn with a 6H or 4H lead. The Figure shows the different lead grades.
A compass is an instrument used to draw circles and arcs. A compass is especially useful for large circles, but using one can be time-consuming. Use a template, whenever possible, to make circles or arcs more quickly.
There are several basic types of compasses. A bow compass, shown in Figure, is used for most drawing applications. A beam compass consists of a bar with an adjustable needle, and a pencil or pen attachment for swinging large arcs or circles. Also available is a beam that is adaptable to the bow compass. This adapter works only on a bow compass that has a removable leg.
Dividers are used to transfer dimensions or to divide a distance into several equal parts. Dividers are also used in navigation to measure distance in nautical miles. Some
prefer to use bow dividers because the centre wheel provides the ability to make fine adjustments easily. Besides, the setting remains more stable than with standard friction dividers.
A functional divider should not be too loose or tight. It should be easy to adjust with one hand. You should always control a divider with one hand as you layout equal increments or transfer dimensions from one feature to another. Do not try to use a divider as a compass. The Figure shows how to handle the divider when used.
Proportional dividers are used to reduce or enlarge an object without having to make mathematical calculations or scale manipulations. The centre point of the divider is set at the correct point for the proportion you want. Then you measure the original size line with one side of the proportional divider; the other side automatically determines the new reduced or enlarged size.
The parallel bar slides up and down a drafting board to allow you to draw horizontal lines. Use triangles with the parallel bar to draw vertical lines and angles. The parallel bar was common for
because architectural drawings are frequently very large. Architects
using manual drafting often need to draw straight lines the full length of their boards, and the parallel bar is ideal for such lines.
There are two standard triangles. The 30º–60º triangle has angles of 30–60–90. The 45 triangle has angles of 45–45–90. Some drafters prefer to use triangles in place of a vertical drafting machine scale, as shown in Figure. Use the machine protractor or the triangle to make angled lines. Using parallel bars, drafters utilize triangles to make vertical and angled lines.
Triangles can also be used as straightedges to connect points for drawing lines without the aid of a parallel bar or machine scale. Use triangles individually or in combination to draw angled lines in 15 increments Also available are adjustable triangles with built-in protractors that are used to make angles of any degree up to a 45 angle.
Manual drafting templates are plastic sheets with accurate shapes cut out for use as stencils to draw specific shapes. The most common manual drafting templates are circle templates for drawing circles and arcs. Templates for drawing other shapes, such as ellipses, and for letters are also common. Templates are also available for specific requirements and drafting disciplines. For example, use architectural templates to draw the floor plan and other symbols to scale. Electronic drafting templates have schematic symbols for electronic schematic drawings.
Circle templates are available with circles in a range of sizes beginning with 1/16 in. (1.5 mm). The circles on the template are marked with their diameters and are available in fractions, decimals, or millimetres. Figure 2.10 shows the parts of a circle. A popular template is one that has circles, hexagons, squares, and triangles.
Always use a circle template rather than a compass. Circle templates save time and are very accurate. For best results, when making circles, keep your pencil or pen perpendicular to the paper. To obtain proper width lines with a pencil, use a 0.9 mm automatic pencil.
An ellipse is a circle seen at an angle. Isometric circles are ellipses aligned with the horizontal right or left planes of an isometric box. Isometric ellipse templates automatically position the ellipse at the proper angle of 35 16'.
, commonly called
, are curves that have no constant radii. A radius curve is composed of a radius and a tangent. The radius on these curves is constant and ranges from 3 ft to 200 ft. (900–60,000 mm). Irregular curves are commonly used in highway drafting. Ship's curves are also available for layout and development of ships hulls. The curves in a set of ship's curves become progressively larger and, like French curves, have no constant radii. Flexible curves are also available that allow you to adjust to the desired curve.
is a machine that mounts to the table or board and has scales attached to an adjustable head that rotates for drawing angles. When locked in a zero position, the scales allow drawing horizontal and vertical lines and perpendicular lines at any angle orientation. The drafting machine vernier head allows you to measure angles accurately to 5' (minutes). Drafting machines, for the most part, take the place of triangles and parallel bars. The drafting machine maintains a horizontal and vertical relationship between scales, which also serve as straightedges. A protractor allows the scales to be set quickly at any angle.
There are two types of drafting machines: arm and track. The track machine generally replaced the arm machine in the history of manual drafting. A major advantage of the track machine is that it allows the drafter to work with a board in the vertical position. A vertical drafting surface position is generally more comfortable to use than a horizontal table. When ordering a drafting machine, the speciﬁcations should relate to the size of the drafting board on which it is mounted. For example, a 37½ 3 60 in. (950–1500 mm) machine properly ﬁts a table of the same size.
Arm Drafting Machine
The arm drafting machine is compact and less expensive than a track machine. The arm machine clamps to a table and through an elbowlike arrangement of supports allows you to position the protractor head and scales anywhere on the board. The Figure shows an arm drafting machine.
Track Drafting Machine
A track drafting machine has a traversing arm that moves left and right across the table and a head unit that moves up and down the traversing arm. There is a locking device for both the head and the traversing arm. The shape and placement of the controls of a track machine vary with the
, although most brands have the same operating features and procedures.
is an instrument with a system of ordered marks at ﬁxed intervals used as a reference standard in measurement. A scale establishes a proportion used in determining the dimensional relationship of an actual object to the representation of the same object on a drawing. Use speciﬁc scales for mechanical, architectural, civil, and metric drawings.
Manual drafters use scales as measurement instruments to help create scaled drawings. In a CADD work environment, a scale is useful for sketching and taking measurements, as well as for related tasks. The scale is a universal and critical
design and drafting
There are four basic scale shapes, as shown in Figure. The two-bevel scale is also available with chuck plates for use with standard arm or track drafting machines. Drafting machine scales have typical calibrations, and some have no scale reading for use as a straightedge. Drafting machine scales are purchased by designating the length needed—12, 18, or 24 in.—and the scale calibration such as metric, engineer's full scale in tenths and half-scale in twentieths, or architect's scale 1/4" 5 1' –0". Many other scales are available. The triangular scale is commonly used in drafting and has different scale calibrations on each corner of the triangle. Common triangular scales are the architectural scale calibrated in feet and inches, mechanical scale calibrated in decimal inches, civil scale calibrated in feet and tenths of a foot, and the metric-scale calibrated in millimetres and centimetres.
Drawings are scaled so that the objects represented can be illustrated clearly on standard sizes of paper. It would be difﬁcult, for example, to make a full-size drawing of a house. You must decrease the displayed size, or scale, of the house to ﬁt properly on a sheet. Another example is a very small machine part that requires you to increase the drawing scale to show necessary detail. Machine parts are often drawn full size or even two, four, or ten times larger than full size, depending on the actual size of the part.
The selected scale depends on:
The actual size of the objects
The amount of detail to
The media size.
The amount of dimensioning and notes
In addition, you should always select a standard scale that is appropriate for the drawing and drafting discipline. The drawing title block usually indicates the scale at which most views are drawn or the predominant scale of a drawing. If the scale of a view differs from that given in the title block, the unique scale typically appears as a note below the corresponding view.
Mechanical Engineer's Scale
scale is commonly used for mechanical drafting when drawings are in fractional or decimal inches. The mechanical engineer's scale typically has full-scale divisions that are divided into 1/16, 10, and 50. The 1/16 divisions are the same as the 16 architect's scale where there are 12 in. and each inch is divided into 1/16 in. increments (or sometimes 1/32 in. divisions). The 10 scale is the same as the 10 civil engineer's scale, where each inch is divided into ten parts, with each division being .10 in. The 50 scale is for scaling dimensions that require additional accuracy because each inch has 50 divisions. This makes each increment 1/30 in. or .02 in. (1 4 50 5 .02). The Figure shows a comparison between the mechanical engineer's scales. The mechanical engineer’s scale also has half-size 1:2 (1/2" 5 1"), quarter-size 1:4 (1/4" 5 1"), and eighth-size 1:8 (1/8" 5 1") options for reducing the drawing scale (see Figure 2.28). Figure 2.29 on page 53 shows a drawing that is represented at full scale (1:1), half-scale (1:2), and quarter-scale (1:4) for comparison.
, as applied here, refers to the material on which you create drawings, such as paper or polyester ﬁlm. The two main types of media used for manual drafting are vellum and polyester ﬁlm, with vellum being the most commonly used. Several factors other than cost also inﬂuence the purchase and use of drafting media, including durability, smoothness, erasability, dimensional stability, and transparency.
Durability is a consideration if the original drawing will be extensively used. Originals can tear or wrinkle, and the images can become difﬁcult to see if the drawings are used often. Smoothness relates to how the medium accepts line work and lettering. The material should be easy to draw on so that the image is dark and sharp without a great deal of effort on your part.
Erasability is important because errors need to be corrected, and changes are frequently made. When images are erased, ghosting—the residue that remains when lines are dif- ﬁcult to remove—should be kept to a minimum. Unsightly ghost images reproduce in a print. Materials that have good erasability are easy to clean. Dimensional stability is the quality of the media to remain unchanged in size because of the effects of atmospheric conditions such as heat, cold, and humidity. Some materials are more dimensionally stable than others.
One thing most designers, engineers, architects, and drafters have in common is that their ﬁnished drawings are intended for reproduction. The goal of every professional is to produce drawings of the highest quality that give the best possible prints when reproduced. Many of the factors that inﬂuence the selection of media for drafting have been described; however, the most important factor in reproduction.
The primary combination that achieves the best reproduction is the blackest and most opaque lines or images on the most transparent base or material. Vellum and polyester ﬁlm make good prints if the drawing is well done. If the only concern is the quality of the reproduction, ink on polyester ﬁlm is the best choice. However, some products have better characteristics than others. Some individuals prefer certain products. It is up to individuals and companies to determine the combinations that work best for their needs and budgets.
SHEET SIZE AND FORMAT
Most professional drawings follow speciﬁc standards for sheet size and format. The Australian Drafting Standard specifies the exact sheet size and format for engineering drawings created for the manufacturing industry. Other disciplines can follow Australian Drafting standards. However, architectural, civil, and structural drawings used in the construction industry generally have a different sheet format and may use unique sheet sizes, such as architectural sheet sizes. Follow sheet size and format standards to improve readability, handling, ﬁling, and reproduction; this will also help ensure that all necessary information appears on the sheet.
When selecting a sheet size, consider the size of objects drawn; the drawing scale; the amount of additional content on the sheet, such as a border, title block, and notes; and drafting standards. In general, choose a sheet size that is large enough to show all elements of the drawing using an appropriate scale and without crowding. For example, the dimensioned views of a machine part that occupies a total area of 15 in. 3 6 in. (381 mm 3 153 mm), can typically ﬁt on a 17 in. 3 11 in. (B size) or 420 mm 3 297 mm (A3 size) sheet.
Diazo prints are also known as ozalid dry prints and blue-line prints. The diazo reproduction process has been mostly replaced by photocopy reproduction and the use of CADD ﬁles for printing and plotting. Diazo printing uses a process that involves an ultraviolet light passing through a translucent original drawing to expose a chemically coated paper or print material under-neath. The light does not go through the dense, black lines on the original drawing, so the chemical coating on the paper beneath the lines remains. The print material is then exposed to ammonia vapour, which activates the remaining chemical coat-ing to produce blue, black, or brown lines on a white or colour-less background. The print that results is a diazo, or blue-line print, not a blueprint. The term blueprint is a generic term used to refer to diazo prints even though they are not true blueprints. Originally, the blueprint process created a print with white lines on a dark blue background.
Photocopy printers are also known as
when used in an engineering or architectural environment. A photocopy printer is a machine for photographically reproducing material, especially by xerography. Xerography is a dry photographic or photocopying process in which a negative image formed by a resinous powder on an electrically charged plate is electrically transferred to and ﬁxed as a positive image on a paper or other copying surface. Prints can be made on bond paper, vellum, polyester ﬁ lm, coloured paper, or other translucent materials. The reproduction capabilities also include instant print sizes ranging from 45 percent to 141 percent of the original size.
Larger or smaller sizes are possible by enlarging or reducing in two or more steps. Almost any large original can be converted into a smaller-sized reproducible print, and then the secondary original can be used to generate additional photocopy prints for distribution, inclusion in manuals, or for more convenient handling. In addition, a random collection of mixed-scale drawings can be enlarged or reduced and converted to one standard scale and format. Reproduction clarity is so good that halftone illustrations (photographs) and solid or ﬁne line work have excellent resolution and density.
The photocopying process and
CADD printing and plotting
have mostly replaced the diazo process. Photocopying has many advantages over diazo printing, including quality repro-duction in many sizes, use of most common materials, and no hazardous ammonia. A CADD system allows you to produce a quality hard copy print quickly. A hard copy is a physical drawing produced by a printer or plotter. The hard copy can be printed on vellum for further reproduction using the diazo or photocopy process.
PROPERLY FOLDING PRINTS
Prints come in a variety of sizes ranging from small, 8½ 3 11 in., to 34 3 44 in. or larger. It is easy to ﬁ le the 8½ 3 11 in. size prints because standard ﬁle cabinets are designed to hold this size. There are ﬁle cabinets available called ﬂat ﬁles that can be used to store full-size unfolded prints. However, many companies use standard ﬁle cabinets. Larger prints must be properly folded before they can be ﬁled in a standard ﬁle cabinet. It is also important to fold a print properly if it is to be mailed.
Folding large prints is much like folding a road map. Folding is done in a pattern of bends that results in the title block and sheet identiﬁ cation ending up on the front. This is desirable for easy identiﬁ cation in the ﬁle cabinet. The proper method used to fold prints also aids in unfolding or refolding prints.
Microfilm is photographic reproduction on ﬁlm of a drawing or other document that is highly reduced for ease in storage and sending from one place to another. When needed, equipment is available for enlargement of the microﬁ lm to printed old vellum becomes yellowed and brittle. In addition, in case of a ﬁre or other kind of destruction, originals can be lost and endless hours of drafting vanish. For these and other reasons, microﬁlm has been used for storage and reproduction of original drawings. Although microﬁlm storage of old drawings still exists in some companies, CADD ﬁles have replaced the use of microﬁlm for most modern applications.
CADD VERSUS MICROFILM
Microﬁlm was once an industry standard for storing and accessing drawings. Large international companies especially relied on the microﬁlm network to ensure that all worldwide subcontractors, vendors, clients, and others involved with a project were able to reproduce needed draw-ings and related documents. One advantage of microﬁlm was the ability to archive drawings—that is, store some-thing permanently for safekeeping.
The use of CADD in the engineering and construction industries has made it possible to create and store drawings electronically on a computer, optical disk, or other media. This makes it possible to retrieve stored drawings easily and quickly. A big advantage of CADD ﬁle storage involves using CADD drawings. When you retrieve CADD-generated drawings, they are of the same quality as when they were originally drawn. You can use CADD drawings to make multiple copies or to redesign a product efﬁciently. In addition to the maintained original quality of the stored CADD drawing, the drawing ﬁle can be sent anywhere in the world over the Internet or within a company's intranet. The Internet is a worldwide network of communication between computers, and intranet links computers within a company or an organization.
The optimum efﬁciency of design and manufacturing methods is achieved without producing a single paper copy of a drawing of a part. Computer networks can directly link engineering and manufacturing departments by integrating computer-aided design (CAD) and computer-aided manufacturing or machining (CAM) software. This integration is referred to as CAD/CAM. The drafter or designer creates a 3-D model or 2-D engineering drawing of a part using CADD software. CAM software is then used to convert the geometry to computer numerical control (CNC) data that is read by the numerically controlled machine tools. Often, the CAD/CAM system is electronically connected to the machine tool. This electronic connection is called networking. This direct link is referred to as direct numerical control (DNC), and it requires no additional media such as paper, disks, CDs, or tape to transfer information from engineering to manufacturing.
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