If “a picture can paint a thousand words,” then drafting is the universal language. Drafting is a specialized drawing style engineers and designers use to convey and record ideas or information necessary for the construction of structures and machines. Drafting follows clearly defined usage rules to ensure that it conveys the same meaning at all times. Those who learn the rules can interpret exactly what a drawing presents. In contrast to pictorial drawings, such as landscapes and portraits, engineering drawings use a graphical language to describe every integral part of an object. As an engineering technician, you will specialize in engineering drawings.
In this collection of lessons, you will learn that drafting divides into the following classifications: technical and illustrative, mechanical and freehand, and engineering. You will also learn about charts, graphs, drafting guidelines, and a variety of instruments and materials designed to help you perform your drafting duties. This unit also contains helpful hints about operating, adjusting, and maintaining your drafting instruments.
When you have completed this lesson, you will be able to:
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1.0.0 Types of Drafting
2.0.0 Drafting Equipment |
Drafting is classified into categories according to its purpose or how it is accomplished: technical or Illustrative, mechanical or freehand, and engineering.
Drafting may be technical or illustrative. Technical drafting presents technical information in a graphic form. For example, a technical drawing may show the type and proper placement of structural members in a building. Illustrative drafting presents a pictorial image only; an example is a perspective drawing of a proposed structure. The term illustrative drafting is not commonly used in construction drafting. Figure 3-1 shows the same item as an illustrative drawing and a technical drawing.
Figure 3-1 – Illustrative versus technical drafting.
Mechanical drafting is any drawing in which the pencil or pen is guided by mechanical devices, such as compasses, straightedges, and french curves. In contrast, freehand drafting is any drawing in which the pencil or pen is guided solely by the draftsman’s hand. Sketches are the result of freehand drafting. With the exception of lettering, most technical drafting is mechanical.
The term mechanical can also describe certain types of industrial or engineering drawings, regardless of whether the drawings are done mechanically or freehand. Some authorities confine the term, used in this sense, to the drawing of machinery details and parts. Others confine it to the drawing of plumbing, heating, air conditioning, and ventilating systems in structures. In the Seabees, mechanical drawing refers to the arrangements of machinery, utility systems, heating, air conditioning, and ventilating systems.
As a civil engineering technician, you will be concerned primarily with three broad types of engineering drafting:
In performing drafting duties, you will be working from sketches, field notes, or direct instructions from your drafting supervisor. Figure 3-2 shows examples of each type of drafting.
Figure 3-2 – Examples of topographic, construction, and administrative drafting.
Graphic presentation of engineering data means using charts and graphs, rather than numerical tables or word descriptions, to present statistical engineering information. A properly constructed chart or graph offers a sharp, clear, visual statement about a particular aspect or series of related facts, emphasizing the numerical value of the facts or showing the way these facts are related.
A chart or graph that emphasizes numerical value is called quantitative; one that emphasizes relationships is called qualitative. The trend of an activity over a period of time, such as the mishaps summary report of a deployed unit rendered over a 6-month deployment period, is more memorable from the shape of a curve describing the trend than from numerical statistics. Successful graphic presentation of engineering data requires as much drafting ability as the graphic representation of engineering objects. Lines must be sharp, opaque, well contrasted, and of uniform weight. Drafters normally execute letters and figures with the standard lettering set according to accepted conventions.
Charts and graphs can be technical or display charts.
Technical engineering charts are usually based on a series of measurements of laboratory experiments or work activities. Such measurements examine the quantitative relationship between a set of two factors or variables. Of the two variables, one has either a controlled or regular variation and is called the independent variable. The other is called the dependent variable because its values are related to those of the independent variable. The line connecting plotted points is called a curve, although it may be broken, straight, or curved. The curve demonstrates the relationship between the variables and permits reading approximate values between plotted points.
The purpose of display charts is to convey data to nontechnical audiences. The message presents a general picture of a situation, usually comparative. There are many varieties of display charts, including bar charts, status charts, and training aids.
Good planning, organization, and supervision lead to efficient job operation and completion. Statistics based on the results of past jobs with similar working conditions provide a basis for predicting the amount of time that a proposed job will take. Graphic presentation of past and current statistical data allows for easy comparison.
These statistics offer the best possibilities for study when presented graphically, usually in the form of a curve. The prediction of expected achievement is usually presented as a bar chart called a time-and-work schedule. When the scheduled work progress is compared with the actual progress (work in place), the chart is called a progress chart.
As stated earlier, definite guidelines in drafting provide uniform interpretation of all engineering drawings such as the Architectural Graphic Standards. In exceptional cases, you may devise your own symbols as long as you adequately explain with notes or a legend any nonstandard features in your drawing.
Many drawings continue in use for years; occasionally, you will have to work with drawings containing obsolete symbols. Look for a legend on the drawings; it should help you identify unfamiliar symbols. If there is no legend, studying the drawing carefully should enable you to interpret the meaning of unfamiliar symbols and abbreviations.
The following civilian industry standards should be on hand in the drafting room:
| ANSI Y14.1 | Drawing Sheet Size and Format |
| ANSI Y14.2 | Line Conventions and Lettering |
| ANSI Y14.3 | Multi and Sectional View Drawings |
| ANSI Y14.5-82 | Dimensioning and Tolerancing for Engineering Drawings |
| AWS A3.0-85 | Welding Terms and Definitions Standards |
| ASTM E380 | Standard for Metric Use |
To be a proficient draftsman, you must be familiar with the tools of your trade and the proper techniques of using them. You should carefully choose your drafting equipment and accessories. Owning a few good pieces of equipment is much better than having a large selection of undependable and shoddy equipment.
The supply department stocks most of the consumable items contained in the kit, such as pencils, pencil leads, lead holders, masking tape, and ink, for kit replenishment. It should also stock additional drafting equipment and supplies, such as pointers and dust brushes, in most drafting rooms to supplement the drafting kits.
The following sections will acquaint you with general drafting equipment and supplies, placing emphasis on items used by Seabee draftsmen.
Materials on which draftsmen draw are called drafting media. There are three basic types: paper, cloth, and film. As a draftsman, you will commonly use tracing paper, profile paper, plan/profile paper, and cross-section paper. Illustration board is used for preparing signs and charts.
Tracing paper (also called tracing vellum) is a high-grade white (or slightly tinted) transparent paper that takes pencil well and erases cleanly. You can make reproductions directly from pencil drawings on tracing paper; however, for better results in reproduction, you will usually ink over a pencil drawing on tracing paper. See Figure 3-3.
Figure 3-3 – Tracing paper.
Profile, plan/profile, and cross-section paper are called gridded media. Each type of gridded media is designed for a specific purpose. Most gridded media EAs use are suitable for reproduction.
Profile paper is normally available in two grid patterns: 4 by 20 lines (4 lines vertical and 20 lines horizontal) per inch and 4 by 30 lines per inch with the vertical lines accented every 10th line. Horizontal lines on the 4 by 20 are accented medium-weight every 5th line and heavyweight every 50th line. Horizontal lines on the 4 by 30 have heavyweight accent lines every 25th line. Profile paper is generally used for road design profiles.
Plan/profile paper has rulings and grid accents similar to those of 4 by 20 and 4 by 30 profile paper, except that the grid patterns occupy only the lower half of the paper. The upper half is plain paper, used to draw the plan view in relation to the profile or to add explanatory notes to the profile. Plan/profile paper is also used for road design.
Cross-section paper, also known as graph paper, is available in a variety of grid patterns. Generally, the engineering technician uses graph paper with a grid scale of 10 by 10 lines per square inch for drawing road cross sections, rough design sketching, preparing schedules, plotting graphs, and many other uses. See Figure 3-4.
Figure 3-4 – Cross-section paper.
Most drafting media are available in three styles: plain sheets or rolls, preprinted sheets with borders and title blocks, and sheets with non-reproducible grids. For further information on the many varieties of drafting media available, refer to suppliers’ catalogs.
Illustration board is drawing paper with a high rag content mounted on cardboard backing. See Figure 3-5.
Figure 3-5 − Illustration board.
The type normally found in a drafting section has a smooth white drawing surface that takes ink readily. Normally, the board is 30 inches by 40 inches and comes in 50-sheet packages. Engineering techs use illustration board for making signs and for large unmounted charts and for mounting maps, photos, and drawings that require a strong backing. They also use a thinner board, called bristol board, for making small signs and charts. The thickness of bristol board is about the same as an ordinary index card. Unlike illustration board, bristol board has two white smooth sides that take ink very well. Bristol board is less expensive than illustration board and you can easily cut, to size with a paper trimmer. It is available in many sizes; the most popular size is 20 inches by 30 inches in 50- or 100- sheet packages.
Two types of pencils are used in drafting: wooden and mechanical. The latter is actually a lead holder and may be used with leads of different hardness or softness.
Drafting pencils are graded according to the relative hardness of their graphite lead. A soft pencil is designated by the letter B, a hard pencil by the letter H. Figure 3-6 shows 17 common grades of drafting pencils from 6B (the softest and the one that produces the thickest line) to 9H (the hardest and one that produces a thin, gray line).
Figure 3-6 − Grades of drafting pencils.
You will notice that the diameters of the lead vary. This feature adds strength to the softer grades. As a result, softer grades are thicker and produce broader lines, while harder grades are smaller and produce thinner lines. Unfortunately, manufacturers of pencils have not established uniformity in grades. Hence, a 3H may vary in hardness from company to company. With experience and preference, you may select the trade name and grade of pencil that suits your needs.
You must be very careful in selecting an eraser to select one that will remove pencil or ink lines without damaging the surface of the drawing sheet.
A vinyl eraser is ideal for erasing lines drawn on tracing cloth and films. An ordinary double-beveled pencil eraser generally comes in red or pink color (sometimes called a pink pearl). A harder eraser (sometimes called a ruby red) is designed for erasing lines in ink. The art gum eraser, made of soft pliable gum, will not mar or scratch surfaces. It is ideally suited for removing pencil or finger marks and smudges.
Figure 3-7 − Common types of erasers
You can also use a kneaded eraser—the type used by artists. It is a rubber dough, kneadable in your hand, and has the advantage of leaving very little debris on the drawing sheet.
Slide 5 of Figure 3-7 shows an electric eraser. The control switch is directly under the fingertip; the body of the machine fits comfortably in the palm of the hand, and the rotating eraser can be directed as accurately as a pencil point. Refills for either ink or pencil erasing are available.
| Caution Do not hold the electric eraser steadily in one spot, or you may wear a hole in, or otherwise damage, the surface of the material you are erasing. When there are many lines close together only one of which needs removing or changing, you can protect the desired lines with an erasing shield, as shown in Figure 3-8. |
Figure 3-8 − Eraser shield.
Finely pulverized gum eraser particles are available in squeeze bottles or in dry clean pads for keeping a drawing clean while you work on it. If you sprinkle a drawing or tracing occasionally with gum eraser particles, then triangles, T squares, scales, french curves, and other equipment not only tend to stay clean themselves, but tend to clean the drawing or tracing as they move over the surface.
Before inking a drawing, you usually prepared it by sprinkling on pounce (a very fine bone dust) and then rubbing in the pounce with a felt pad on the container. Pounce helps to prevent a freshly inked line from spreading. Use a draftsman’s dust brush for brushing dust and erasure particles off a drawing.
Most engineering tech shops are furnished with standard drafting tables with drafting boards, as shown in Figure 3-9. The majority of this furniture is easily adjustable to the users’ needs. The table should be high enough for you to work in a standing position without stooping or holding your arms in a raised position. The drawing board has hinged attachments for adjusting the incline; your line of sight should be approximately perpendicular to the drafting surface. Your drafting stool should be high enough in relation to the table for you to see the whole drafting board but not so high that you are seated uncomfortably.
Figure 3-9 − Drafting tables with boards.
Drafting boards are constructed of joined strips of softwood, usually clear white pine or basswood. They are equipped with hinged attachments for securing the board to a table or fabricated base.
If suitable bases are not available, table bases may be constructed at the unit carpenter shop.
You should consider only the left-hand vertical edge as a working edge for the T square if you are right-handed (the right-hand edge if you are left-handed). You should never use the T square with the head set against the upper or lower edge of the board, as the drafting board may not be perfectly square.
The drafting board should be covered. A variety of good drafting board cover materials is available. Available cover materials are cellulose acetate-coated paper, vinyl, and mylar film. Vinyl drafting board covers have the added advantage of being able to close up small holes or cuts, such as those made by drafting compasses or dividers. In general, drafting board covers protect the drafting board surface by preventing the drafting pencil from following the wood grain, by reducing lighting glare, and by providing an excellent drafting surface.
Since you will be constantly using your eyes, your working area must be well lighted. Natural light is best, if available and ample; although in the majority of cases acceptable natural light will be the exception rather than the rule. Drafting rooms are usually lighted with overhead fluorescent fixtures.
Ordinarily, these fixtures are inadequate in quality and intensity of light. Adjustable lamps will improve the lighting conditions. The most popular type of adjustable lamp is the floating-arm fluorescent fixture that clamps onto the table. Arrange your lighting to come from the front-left, if you are right-handed; from the front right, if you are left-handed. This minimizes shadows cast by drawing instruments and your hands.
Never place your drafting board so that you will be subject to the glare of direct sunlight. North windows are best for admitting daylight in the Northern Hemisphere. Conservation of vision is of the utmost importance. You must make every possible effort to eliminate eyestrain.
The T square gets its name from its shape. It consists of a long, straight strip, called the blade, which is mounted at right angles on a short strip called the head. The head is mounted under the blade so that it will fit against the edge of the drawing board while the blade rests on the surface. T squares vary in size from 15 to 72 inches in length, with 36 inches the most common.
The T square shown in Figure 3-10 is typical of the ones used by an engineering technician. The head is made of hardwood, the blade usually of maple with a natural or mahogany finish. The edges of the blade are normally transparent plastic strips glued into grooves on both edges of the blade, as shown in the cross section in Figure 3-10. This allows the edge of the T square to ride above the drawing as the blade is moved up or down the board. This arrangement is a great advantage when you are drawing with ink. Since the tip of the ruling pen does not come in contact with the blade, but is below it, ink cannot be drawn under the blade to blot the drawing.
Figure 3-10 − Drafting board with T square and drafting paper in place
The T square is used for drawing horizontal lines only. Always draw lines along the upper edge of the blade. The T square also serves as a base for drawing the vertical and inclined lines of a triangle. Some T squares have adjustable heads to allow angular adjustments of the blade.
Handle your T square carefully. If dropped, it may be knocked out of true and become useless. Additionally, to prevent warping, hang the T square by the hole in the end of the blade or lay it on a flat surface so that the blade rests flat. Before beginning a new job, test the top edge of your T square for warp or nicks by drawing a sharp line along the top of the blade.
Turn the T square over and redraw the line with the same edge. If the blade is warped, the lines will not coincide. If the blade swings when the head is held firmly against the edge of the drawing board, the blade may be loose where it is joined to the head, or the edge of the T square head may be warped. You can usually tighten a loose blade by adjusting the screws that connect it to the head, but if it is out of square, warped, or in bad condition, select a new one.
Many draftsmen prefer to use a parallel straightedge (Figure. 3-11) rather than a T square. The primary purpose of the parallel straightedge is the same as the T square.
Figure 3-11 − Parallel straightedge.
The parallel straightedge is a laminated maple blade with transparent plastic edges similar to those on the T square. The parallel straightedge uses a system of cords and pulleys so that it is supported at both ends by a cord tacked to the drawing board. You can move the straightedge up or down the board with pressure at any point along its length and maintain parallel motion automatically. It comes complete with cord, tacks, cord tension adjuster, and mounting instructions. Some straightedges, like the one shown in Figure 3-11, are equipped with a cord lock on one end of the blade. The straightedge is locked into place by turning the cord lock clockwise. This permits use of the straightedge on an inclined board. It also prevents accidental movement when you are inking or using mechanical lettering devices. The advantages of the parallel straightedge become particularly significant when you are working on large drawings. While the T square works well for small work, it becomes unwieldy and inaccurate when you are working on the far right-hand side of large drawings
When drawing long, straight lines, use a steel straightedge (Figure 3-12) because its heavy weight helps keep the straightedge exactly in position. The steel straightedge is also excellent for trimming blueprints and cutting heavy illustration board. Steel straightedges are usually made of stainless steel and are available in lengths of 15 inches to 72 inches The one included in the draftsman kit is 42 inches long. Some have a beveled edge.
Figure 3-12 − Steel straightedge.
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. Triangles are referred to by the size of their acute angles. Figure 3-13 shows two basic drafting triangles: the 45° (each acute angle measures 45°, and the 30°/60° (one acute angle measures 30°; the other, 60°). The size of a 45° triangle is designated by the length of the sides that form the right angle (the sides are equal). The size of a 30°/60° triangle is designated by the length of the longest side that forms the right angle. Sizes of both types of triangles range from 4 inches through 18 inches in 2-inch increments.
Figure 3-13 − 45° and 30°/60° drafting triangles.
Like all other drafting equipment, triangles must be kept in good condition. If you drop a plastic triangle, you may damage its tip. Also, triangles may warp so that they do not lie flat on the drawing surface, or the edge may deviate from true straightness. To prevent warping or chipping, always lay them flat or hang them up when you are not using them. Since there is seldom enough drawer space available to permit laying triangles flat, develop the habit of hanging them up. If the tips are bent, use a sharp knife to cut off the damaged part. If the triangle is warped, you may be able to bend it back by hand. If this does not straighten it, leave the triangle lying on a flat surface with weights on it or hold the triangle to the opposite curvature with weights. If the triangle becomes permanently warped so that the drawing edges are curved or the angles are no longer true, throw it away and get another. To test the straightness of a triangle, place it against the T square and draw a vertical line, as shown in Figure 3-14. Then reverse the triangle and draw another line along the same edge. If the triangle is straight, the two lines will coincide; if they do not, the error is one-half the resulting space.
Figure 3-14 − Testing a triangle for straightness.
Protractors are used for measuring and laying off angles other than those drawn with the triangle or a combination of triangles. Most of the work you will do with a protractor will involve plotting information obtained from field surveys. Like the triangle, most protractors are made of transparent plastic. They are available in 6-, 8-, and 10-inch sizes and are either circular or semicircular in shape, as shown in Figure 3-15.
Figure 3-15 − Types of protractors.
The protractors that engineering technicians use are usually graduated in increments of 1/2°. By careful estimation, you may obtain angles of 1/4°. Protractor numbering arrangement varies. Semicircular protractors are generally labeled from 0° to 180° in both directions. Circular protractors may be labeled from 0° to 360° (both clockwise and counterclockwise), or they may be labeled from 0° to 90° in four quadrants. Stow and care for protractors in the same manner as triangles.
The adjustable triangle, shown in Figure 3-16, combines the functions of the triangle and the protractor. When it is used as a right triangle, you can set and lock the hypotenuse at any desired angle to one of the bases.
Figure 3-16 − Adjustable triangle.
The transparent protractor portion is equivalent to a protractor graduated in 1/2° increments. The upper row of numbers indicates angles from 0° to 45° to the longer base; the lower row indicates angles from 45° to 90° to the shorter base. By holding either base against a T square or straightedge, you can measure or draw any angle between 0° and 90°.
The adjustable triangle is especially helpful in drawing building roof pitches. It also allows you to transfer parallel inclined lines by sliding the base along the T square or straightedge.
Use irregular curves (called french curves) for drawing smooth curved lines other than arcs or circles, lines such as ellipses, parabolas, and spirals. Transparent plastic french curves come in a variety of shapes and sizes.
Figure 3-17 shows an assortment of french curves. In such an assortment, you can find edge segments you can fit to any curved line you need to draw.
Figure 3-17 − French curves.
Stow and care for french curves in the same manner as triangles.
So far we have discussed only those instruments and materials you will need for drawing straight lines (with the exception of french curves). Many drawings you prepare will require circles and circular arcs. Use instruments contained in a drawing instrument set for this purpose. Many types of drawing instrument sets are available; however, it is sometimes difficult to judge the quality of drafting instruments by appearance alone. Often their characteristics become evident only after use.
The drawing instrument set shown in Figure 3-18 is typical of sets in the standard draftsman kit. The following sections describe these instruments as well as some special-purpose instruments not found in the set. These special-purpose instruments may be purchased separately or found in other instrument sets.
Figure 3-18 − Drawing instrument set.
Circles and circular curves of relatively short radius are drawn with compasses. The large pivot joint compass is satisfactory for drawing circles of 1 inch to about 12 inch 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 has a setscrew for mounting a pen or pencil attachment on the compass. You can insert an extension bar to increase the radius of the circle drawn. The other type of compass in the drawing instrument set is the bow compass. Many experienced draftsmen prefer the bow compass over the pivot joint compass. The bow compass is much sturdier and is capable of taking the heavy pressure necessary to produce opaque pencil lines without losing the radius setting.
There are two types of bow compasses. The location of the adjustment screw determines the type. The bow pen/pencil in Figure 3-18 is the center adjustment type, whereas the bow drop pen in Figure 3-19 is the side adjustment type.
Figure 3-19 – Bow instruments: bow pen/pencil; bow divider, bow drop pen drawing instrument set
Each type comes in two sizes: large and small. Large bow compasses are usually of the center adjustment type, although the side adjustment type is available. The large bow compasses are usually about 6 inches long, the small compasses approximately 4 inches long. Extension bars are available for large bow compasses. Bow compasses are available as separate instruments, or as combination instruments with pen and pencil attachments. Most compasses have interchangeable needle points. Use the conical or plain needlepoint when you use the compass as dividers. Use the shoulder-end needlepoint with pen or pencil attachments. When you draw many circles using the same center, the compass needle may bore an oversized hole in the drawing. To prevent these holes, use a device called a horn center or center disk. Place this disk over the center point. Then place the point of the compass needle into the hole in its center.
Dividers are similar to compasses, except that both legs have needlepoints. The instrument set (Figure 3-18) contains two different types and sizes of dividers: large 6- inch hairspring dividers and small center adjustment bow dividers (Figure 3-19). You can also use the large pivot joint compass (Figure 3-19) as dividers. As with compasses, dividers are available in large and small sizes, and in pivot joint, center adjustment bow, and side adjustment bow types. Figure 3-20 shows a small side adjustment bow divider. Use pivot joint dividers for measurements of approximately 1 inch or more. For measurements of less than 1 inch, use bow dividers. You can also use dividers to transfer measurements, step off a series of equal distances, and divide lines into a number of equal parts.
Figure 3-20 – Bow divider.
The drop bow pen (Figure 3-21) is not one of the standard instruments, but it is essential for some jobs. Use it to ink small circles with diameters of less than 1/4 inch. As the name indicates, the pen assembly is free to move up and down and to rotate around the main shaft. When using this instrument, hold the pen in the raised position, adjust the setscrew to give the desired radius, and then gently lower the pen to the paper surface and draw the circle by rotating the pen around the shaft.
Figure 3-21 – Drop bow pen
Figure 3-22 shows the three shapes in which compasses and dividers are made: round, flat, and bevel.
Figure 3-22 – Shapes of compasses and dividers.
Figure 3-23 shows two most common types of pivot joints on compasses and dividers.
Figure 3-23 – Sections of pivot joints.
When you select compasses and dividers, test them for alignment by bending the joints and bringing the points together. New instruments are factory adjusted for correct friction setting. They rarely require adjustment. Use a small jeweler’s screwdriver or the screwdriver found in some instrument sets for adjusting most pivot joint instruments. Skilled instrument repairmen should adjust instruments that require a special tool.
Adjust pivot joint compasses and dividers so that they can be set without undue friction. They should not be so rigid that their manipulation is difficult, nor so loose that they will not retain their setting.
Divider points should be straight and free from burrs. When the dividers are not in use, protect the points by sticking them into a small piece of soft rubber eraser or cork. When points become dull or minutely uneven in length, make them even by holding the dividers vertically, placing the legs together, and grinding them lightly back and forth against a whetstone. (See Figure 3-24A.) Then hold the dividers horizontally and sharpen each point by whetting the outside of it back and forth on the stone, while rolling it from side to side with your fingers (Figure 3-24B). The inside of the leg should remain flat and not be ground on the stone. Do not grind the outside of the point so that a flat surface results. In shaping the point, be careful to avoid shortening the leg.
Figure 3-24 – Divider maintenance (A) Evening the legs of dividers; (B) Sharpening divider needlepoints.
Keep needles on compasses and dividers sharpened to a fine taper. When pushed into the drawing, they should leave a small, round hole in the paper no larger than a pinhole. Since the same center is often used for both the compasses and dividers, it is best that needles on both be the same size. If the compass needle is noticeably larger, grind it until it is the correct size.
To make a compass needle smaller, wet one side of the whetstone and place the needle with its shoulder against this edge. Then grind it against the whetstone, twirling it between your thumb and forefinger (Figure 3-25).
Figure 3-25 – Shaping a compass needle.
Test it for size by inserting it in a hole made by another needle of the correct size. When pushed as far as the shoulder, it should not enlarge the hole. The screw threads on bow instruments are delicate. Because of this, take care never to force the adjusting nut. Threads must be kept free from rust or dirt. If possible, keep drawing instruments in a case, since the case protects them from damage by falls or unnecessary pressures. Also, the lining of the case is usually treated with a chemical that helps prevent the instruments from tarnishing or corroding.
To protect instruments from rusting when they are not in use, clean them frequently with a soft cloth and apply a light film of oil to their surface with a rag. Do not oil joints on compasses and dividers. When the surface finish of instruments becomes worn or scarred, it is subject to corrosion; therefore, never use a knife edge or an abrasive to clean drafting instruments.
The beam compass (Figure 3-26) is used for drawing circles with radii larger than can be set on a pivot joint or bow compass. Both the needlepoint attachment and the pen or pencil attachment on a beam compass are slide-mounted on a metal bar called a beam. You can lock the slide-mounted attachments in any desired position on the beam. Thus, a beam compass can draw circles of any radius up to the length of the beam. With one or more beam extensions, the length of the radius of a beam compass ranges from about 18 inches to 70 inches.
Figure 3-26 – Beam Compass.
Proportional dividers (Figure 3-27) are used for transferring measurements from one scale to another. This capability is necessary to make drawings to a larger or smaller scale. Proportional dividers can divide lines or circles into equal parts.
Figure 3-27 – Proportional dividers.
Proportional dividers consist of two legs of equal length, pointed at each end, and held together by a movable pivot. By varying the position of the pivot, you can adjust the lengths of the legs on opposite sides of the pivot so that the ratio between them is equal to the ratio between two scales. Therefore, a distance spanned by the points of one set of legs has the same relation to the distance spanned by the points of the other set as one scale has to the other. On the proportional dividers, a thumb nut moves the pivot in a rack-and-gear arrangement. When you reach the desired setting, a thumb-nut clamp on the opposite side of the instrument locks the pivot in place. A scale and vernier on one leg facilitate accurate setting.
On less expensive models, the movable pivot is not on a rack and gear, and there is no vernier. Set the dividers by reference to the table of settings that comes with each pair; they will accommodate varying ranges of scales from 1:1 to 1:10. However, do not depend entirely on the table of settings. You can check the adjustment by drawing lines representing the desired proportionate lengths, and then applying the points of the instrument to each of them in turn until, by trial and error, you reach the correct adjustment.
To divide a line into equal parts, set the divider to a ratio of 1 to the number of parts desired on the scale marked Lines. For instance, to divide a line into three parts, set the scale at 3. Measure off the length with points of the longer end. The span of the points at the opposite ends will be equal to one-third the measured length. To use proportional dividers to transfer measurements from feet to meters, draw a line 1 unit long and another line 3.28 units long and set the dividers by trial and error accordingly.
Some proportional dividers have an extra scale for use in getting circular proportions. The scale marked Circle indicates the setting for dividing the circumference into equal parts. The points of the dividers are of hardened steel, and if you handle them carefully, these points will retain their sharpness during long use. If they are damaged, you may sharpen them and the table of settings will still be usable, but the scale on the instrument will no longer be accurate.
In one sense, the term scale means the succession of graduations on any graduated standard of linear measurement, such as the graduations on a steel tape or a thermometer. In another sense, when we refer to the “scale of a drawing,” the term means the ratio between the dimensions of the graphic representation of an object and the corresponding dimensions of the object itself.
Suppose, for example, that the top of a rectangular box measures 6 inches by 12 inches, if you draw a 6-inch by 12-inch rectangle on the paper, the dimensions of the drawing would be the same as those of the object. The drawing would, therefore, be a full-scale drawing. This scale could be expressed fractionally as 1/1, or it could be given as 1 inch = 1 inch.
Suppose that instead of making a full-scale drawing, you decided to make a half-scale drawing. You should then draw a 3-inch by 6-inch rectangle on the paper. This scale could be expressed fractionally as 1/2, or it could be given as 1 inch = 2 inches, or as 6 inches = 1 foot. In this case, you made the drawing on a smaller scale than the scale of the original object, the scale of an original object being always 1/1, or unity. The relative size of a scale is indicated by the fractional representation of the scale. A scale whose fractional representation equals less than unity is a less-than-full scale. One whose fractional representation is greater than unity (such as a scale of 200/1) is a larger-thanfull scale. A scale of 1/10,000 is, of course, smaller than a scale of 1/100.
A scale expressed as an equation can always be expressed as a fraction. For example, the scale of 1 inch = 100 feet, expressed fractionally, comes to 1 over (100 x 12), or 1/1,200. Obviously, any object larger than the drawing paper on which it is to be represented must be “scaled down” (that is, reduced to less than- full scale) for graphic representation.
Conversely, it is often desirable to represent a very small object on a scale larger than full scale for clarity and to show small details. Because the drawings an engineering technician prepares frequently require scaling down, the following discussion refers mostly to that procedure. However, scaling up rather than down simply means selecting a larger-than full scale rather than a smaller-than-full scale for your drawing. You could, if necessary, determine the dimensions of your drawing by arithmetical calculation; for example, on a half-scale drawing, you divide each of the actual dimensions of the object by 2. However, this might be a time consuming process if you were drawing a map of a certain area to a scale of 1 inch = 1,000 miles, or 1/6,335,000 feet. Consequently, you will usually scale a drawing up or down by the use of one or another of a variety of scales. This sense of the term scales refers to a graduated, ruler-like instrument on which you can determine scale dimensions for a drawing by inspection.
Scales vary in types of material, shapes, style of division, and scale graduations. Good quality scales are made of high-grade boxwood or plastic, while inexpensive scales are sometimes made of yellow hardwood. The boxwood scales have white plastic scale faces permanently bonded to the boxwood. The graduation lines on the boxwood scales are cut by a highly accurate machine. Plastic scales, less expensive than boxwood scales, have clear graduations and are reasonably accurate.
Scales are generally available in four different shapes, as shown in Figure 3-28.
Figure 3-28 – Types of scales in cross section.
The numbers in the figure indicate the location of the scale face. The triangular scale provides six scale faces on one rule. The two-bevel flat scale provides two scale faces on one side of the rule only. The opposite-bevel flat scale provides two scale faces, one on each side of the rule. And the four-bevel flat scale provides four scale faces, two on each side of the rule. The most common types of scales are the architect’s, the engineer’s, the mechanical engineer’s, and the metric.
To gain a better understanding of the architect and engineer’s scale, both of which the following sections will describe, having the actual scales at hand as you study may be helpful.
Architect’s scales are usually triangular and are used wherever dimensions are measured in feet and inches. Major divisions on the scale represent feet; those divisions are subdivided into 12ths or 16ths, depending on the individual scale.
Figure 3-29 shows the triangular architect’s scale and segments of each of the eleven scales found on this particular type of scale. Notice that all scales except the 16th scale are actually two scales read either from left to right or right to left. When reading a scale numbered from left to right, notice that the numerals are closer to the outside edge. On scales numbered from right to left, notice that the numerals are closer to the inside edge.
Figure 3-29 – Architect’s scale.
Architect’s scales are “open” divided (only the main divisions are marked throughout the length), with the only subdivided interval an extra interval below the 0-foot mark. These extra intervals are divided into 12ths. To make a scale measurement in feet and inches, lay off the number of feet on the main scale and add the inches on the subdivided extra interval. However, notice that the 16th scale is fully divided with its divisions divided into 16ths.
Now let's measure off a distance of 1 foot 3 inches to see how to read each scale and how the scales compare to one another. (Refer to Figure 3-29.) Since the graduations on the 16th scale are subdivided into 16ths, we will have to figure out that 3 inches actually is 3/12 or 1/4 of a foot. Changing this to 16ths, we now see we must measure off 4/16ths to equal the 3-inch measurement. Note carefully the value of the graduations on the extra interval, which varies with different scales. On the 3 inches = 1 foot scale, for example, the space between adjacent graduations represents one-eighth inch. On the 3/32 inches = 1 foot scale, however, each space between adjacent graduations represents 2 inches
The scale 3/32 inches = 1 foot, expressed fractionally, comes to 3/32 = 12, or 1/128. This is the smallest scale provided on an architect’s scale. The scales on the architect’s scale, with their fractional equivalents, are as follows:
| 3 inches = 1 foot | ¼ scale |
| 1 ½ inches = 1 foot | 1/8 scale |
| 1 inch = 1 foot | 1/12 scale |
| ¾ inch = 1 foot | 1/16 scale |
| ½ inch = 1 foot | 1/24 scale |
| 3/8 inch = 1 foot | 1/32 scale |
| ¼ inch = 1 foot | 1/48 scale |
| 1/16 inch = 1 foot | 1/64 scale |
| 1/8 inch = 1 foot | 1/96 scale |
| 3/32 inch = 1 foot | 1/128 scale |
The chain or civil engineer’s, scale, commonly called the engineer’s scale, is usually a triangular scale, containing six fully divided scales subdivided decimally, each major interval on a scale being subdivided into 10ths. Figure 3-30 shows the engineer’s scale and segments of each of the six scales.
Figure 3-30 – Engineer’s scale.
Each of the six scales is designated by a number representing the number of graduations that particular scale has to the linear inch. On the 10 scale, for example, there are 10 graduations to the inch; on the 50 scale, there are 50. You can see that the 50 scale has 50 graduations in the same space occupied by 10 on the 10 scale. This space is 1 linear inch.
To determine the actual number of graduations represented by a numeral on the engineer’s scale, multiply the numeral by 10. On the 50 scale, for instance, the numeral 2 indicates 2 x 10, or 20 graduations from the 0. On the 10 scale, the numeral 11 indicates 11 x 10, or 110 graduations from the 0. Note that the 10 scale is numbered every major graduation, while the 50 scale is numbered every other graduation. Other scales on the engineer’s scale are the 20, 30, 40, and 60.
Because it is decimally divided, the engineer’s scale can be used to scale dimensions down to any scale in which the first figure in the ratio is 1 inch and the other is 10 or a multiple of 10.
Suppose, for example, that you wanted to scale a dimension of 150 mi down to a scale of 1 inch = 60 miles. You would use the 60 scale, allowing the interval between adjacent graduations to represent 1 mile. To measure off 150 miles to scale on the 60 scale, you would measure off 2.5 inches, which falls on the 15th major graduation.
Suppose now that you want to scale a dimension of 6,500 feet down to a scale of 1 inch = 1,000 feet. The second figure in the ratio is a multiple of 10 times a multiple of 10. You would therefore use the 10 scale, allowing the interval between adjacent graduations on the scale to represent 100 feet, in which case the interval between adjacent numerals on the scale would indicate 1,000 feet. To measure off 6,500 feet, you would simply lay off from 0 to 6.5 on the scale.
To use the engineer’s scale for scaling to scales expressed fractionally, you must be able to determine the fractional equivalent of each of the scales. For any scale, this equivalent is simply 1 over the total number of graduations on the scale, or 1 over the product of the scale number times 12, which is the same thing. Applying this rule, the fractional expressions of each of the scales is as follows:
10 scale = 1/120
20 scale = 1/240
30 scale = 1/360
40 scale = 1/480
50 scale = 1/600
60 scale = 1/720
Suppose you want to scale 50 feet down to a scale of 1/120. The 10 scale gives you this scale; therefore, use the 10 scale, allowing the space between graduations to represent 1 foot, and measuring off 5 (for 50 feet). The line on your paper would be 5 inches long, representing a line on the object itself that is 120 inches x 5 inches, or 600 inches, or 50 feet long.
Similarly, if you want to scale 50 feet down to a scale of 1/600, use the 50 scale and measure off 5 for 50 feet. In this case, the line on your paper would be 1 inch long, representing a line on the object itself that is 1 x 600, or 600 inches, or 50 ft long.
When the drawing does not need to be made to a specified scale—that is, when the dimensions of lines on the drawing are not required to bear a specified ratio to the dimensions of lines on the object itself—use the most convenient scale on the engineer’s scale.
Suppose, for example, that you want to draw the outline of a 360-foot by 800-foot rectangular field on an 8-inch, by 10 1/2-inch sheet of paper with no specific scale prescribed. All you want to do is reduce the representation of the object to one that will fit the dimensions of the paper. You could use the 10 scale, allowing the interval between adjacent graduations to represent 10 feet. In this case, the numerals on the scale, instead of representing 10, 20, and so on, will represent 100, 200, and so on. To measure off 360 feet to scale, measure from 0 to the 6th graduation beyond the numeral 3. For 800 feet, measure from 0 to the numeral 8. Because you allowed the interval between adjacent graduations to represent 10 feet, and because the 10 scale has 10 graduations to the inch, the scale of your drawing would be 1 inch = 100 feet, or 1/1,200.
Use the metric scale in place of the architect’s and engineer’s scale when measurements and dimensions are in meters and centimeters. Metric scales are available in flat and triangular shapes. The flat 30-cm metric scale is shown in Figure 3- 31.
Figure 3-31 – Metric scale.
The top scale is calibrated in millimeters and the bottom scale in half millimeters. The triangular metric scale has six fully divided scales, which are 1:20, 1:33 1/3, 1:40, 1:50, 1:80, and 1:100. When using scales on a drawing, do not confuse the engineer’s scale with the metric scale. They are very similar in appearance. Whenever conversions are made between the metric and English system, remember that 2.54 centimeters equals 1 inch.
For use with a triangular scale, a scale clip or scale guard, such as the one shown in Figure 3-32, is very helpful. The clip makes it easy for you to identify what scale you are using. Large spring type paper clips will serve the same purpose when scale clips are not available.
Figure 3-32 – Triangular scale clip.
Map measures are precision instruments for measuring the lengths of roads, pipelines, and other irregular outlines on maps and drawings. Measure distances by first setting the instrument to zero, then tracing the line you are measuring with the small, projecting tracing wheel, like that on the map measures shown in Figure 3-33.
Figure 3-33 – Types of map measures.
In using map measures, do not depend entirely on the indicated numerical scale. Always check it against the graphical scale on the map or drawing. Verify if, for example, 1 inch traversed on the graphical scale really registers 1 inch on the dial; if not, make the proper correction to the distance measured. Actually, a map measure is just another odometer. Odometers are used to measure actual distances, while the map measures are used to measure scaled distances.
There are many ways of indicating the scale on a drawing. Among these are the fractional method, the equation method, and the graphic method.
In the fractional method, the scale is indicated as a fraction or a ratio. A full-size scale is indicated as 1/1; enlarged scale, as 10/1, 4/1, 2/1, etc.; and reduced scale, as 1/2, 1/4, 1/10, etc. Notice that the drawing unit is always given as the numerator of the fraction and the object unit as the denominator. On maps, the reduced scale fraction may be very large (for example, 1/50,000), compared to the typical scales on machine drawings. On maps, the scale is frequently expressed as a ratio, such as 1:50,000. In the equation method, a certain number of inches on the drawing is set equal to a certain length on the object. Symbols are used for feet (') and inches ("). On architectural drawings, a certain number of inches on the drawing is set to equal to 1 foot on the object. A full-size scale is entered as 12" = 1' – 0"; an enlarged scale, as 24" = 1’–0"; and a reduced scale, as 1/8" = 1' – 0". On civil engineering drawings, 1 inch on the drawing is set to equal to a certain measurement on the object: 1" = 5', 1" = 100', 1" = 1 mile.
In the graphic method, an actual measuring scale is shown on the drawing. Typical graphic scales are shown in Figure 3-34. Note that in each case, the primary scale lies to the right of the 0; a subdivided primary scale unit lies to the left of the 0.
Figure 3-34 – Typical graphic scales.
Drafting templates are timesaving devices used for drawing various shapes and standard symbols. They are especially useful when shapes and symbols must appear on the drawing a number of times. Templates are usually made of transparent green or clear plastic. They are available in a wide variety of shapes, including circles, ellipses, hexagons, triangles, rectangles, and arcs. Special templates are available for symbols used on architectural drawings, mechanical drawings, and maps. Templates for almost every purpose are available from the well-known drafting supply companies. Figure 3-35 shows only a few of the more common types of drafting templates.
Figure 3-35 – Drafting Templates.
Frequently, you will prepare inked drawings, maps, or charts that require freehand lines and lettering. Many types of freehand pens are available. But here we will be concerned only with those pens the engineering technician uses. Included in the draftsman kit is a reservoir pen set, which you may use either with a penholder, as a freehand pen, or fitted into a mechanical lettering device for template lettering.
Use the technical fountain pen (sometimes called a Rapidograph pen or reservoir pen) for ruling straight lines of uniform width with the aid of a T square, triangle, or other straightedge. You may also use it for freehand lettering and drawing and with various drawing and lettering templates. One of the best features of the technical fountain pen is its ink reservoir. The reservoir, depending on the style of pen, is either built into the barrel of the pen or is a translucent plastic ink cartridge attached to the body of the pen. The large ink capacity of the reservoir saves time because you do not have to replenish the ink supply constantly. Therefore, many EAs prefer the technical fountain pen to the ruling pen.
A typical technical fountain pen is shown in Figure 3-36. Various manufacturers offer variations in pen style and line size. Some pens are labeled by the metric system according to the line weight they make.
Figure 3-36 – Technical fountain pens.
Other pens are labeled with a code that indicates line width measured in inches. For instance, a No. 2 pen draws a line .026 inches in width. Most technical fountain pens are color-coded for easy identification of pen size. These pens are available either as individual fountain pen units, resembling a typical fountain pen, or as a set, having a common handle and interchangeable pen units. The pen shown in Figure 3-36 is a part of a set of technical fountain pens.
Some reservoir pens for lettering are made so the point section will fit in a Leroy scriber, a system using templates and special scribing tools to create machine-perfect lettering. These pens may also be used for any work that a regular technical fountain pen is used for.
You must hold the technical fountain pen so that it is perpendicular to the drawing surface at all times. If you do not hold the pen in the correct manner, the point will bevel or wear unevenly and eventually form an elliptical point. With the point in this condition, the pen will produce lines of inconsistent widths.
To fill the reservoir of a fountain pen, use the knob on the barrel opposite the point. When you turn the knob counterclockwise, a plunger is forced down into the barrel forcing out any ink remaining in the reservoir. Place the point end of the pen into the ink and turn the knob clockwise to pull the plunger up. As the knob pulls the plunger up, the plunger draws ink through the point, filling the reservoir.
To fill the ink cartridge type of pen shown in Figure 3-37, remove the cartridge from the body and insert the ink bottle dropper all the way into the reservoir cartridge. Place the dropper in contact with the bottom of the reservoir cartridge to prevent the ink from forming air bubbles. Fill the cartridge to approximately three-eighths of an inch from the top, then replace the cartridge and clamp ring.
Figure 3-37 – Technical fountain pen.
The feed tube of the pen point is threaded (Figure 3-37). Along this threaded portion is an inclined channel that allows air to enter the ink reservoir. This channel must be free of dried ink or foreign particles to ensure correct ink flow. When cleaning the pen, scrub the threads and channel with a brush, such as a toothbrush, wetted with a cleaning solution of soap and water. A cleaning pin (a tiny weighted needle) is made to fit into the feed tube and point (Figure 3-37). This cleaning pin assures a clear passage of ink from the reservoir to the point. Usually, a light shake of the pen will set the cleaning pin in motion, removing any particles that settle in the tube when the pen is not in use. (Do not shake the pen over your drawing board.)
If you do not use the pen frequently, the ink will dry, clogging the point and feed tube. When the pen becomes clogged, soak it in pen cleaner or ammonia water until it unscrews with little or no resistance. A better practice is to clean the pen before you put it away if you know in advance that you will not be using it for several days.
You must handle the cleaning pin with care, especially the smaller sizes. A bent or damaged cleaning pin will never fit properly into the feed tube and point.
A draftsman’s drawing ink is commonly called india ink (Figure 3-38).
Figure 3-38 – Drawing Ink.
Drawing ink consists of a pigment (usually powdered carbon) suspended in an ammonia-water solution. Ink thickened by age or evaporation maybe thinned slightly by adding a few drops of a solution of four parts aqua ammonia to one part distilled water. After the ink dries on paper, it is waterproof. Drawing ink is available in many different colors, but for construction and engineering drawings, black ink is preferred for reproduction and clarity. Small 3/4- or 1- oz bottles of black, red, and green ink are found in the standard draftsman kit. Larger bottles are available for refilling the small bottles. The stopper for a small ink bottle is equipped with either a squeeze dropper or a curved pipette for filling pens.
When you are working with ink, always keep the stopper on the ink bottle when you are not filling the pen, and keep the bottle far away from your drawing. Nothing is more frustrating for a draftsman than spilling a bottle of ink on a finished drawing. Special bottle holders are available to minimize this hazard. If you do not have a bottle holder, it would be to your advantage to devise your own.
Many tools other than the ones already presented in this lesson are currently used to create technical drawings. A variety of drafting machines (not in the draftsman kit) are available at several shore-based support activities.
Depending on the requirements of a particular activity, an engineering technician assigned to staff or independent work may also be exposed to a more advanced and sophisticated computer-assisted drafting method. 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 you can move the protractor head over the surface of a drafting table without change in orientation by means of a parallel motion linkage consisting of two sets of double bars. Figure 3-39 shows a rigid metal connecting link or arms, commonly called pin-joint linkage.
Figure 3-39 – Drafting machine.
Another type of drafting machine has two steel bands enclosed in tubes working against one another (Figure 3-39) (although this type may also have the bands without the tubes). If these bands become loose through wear, their tension can be increased. This type of drafting machine is superior to that with pin-point linkage because there is less lost motion.
As an engineering technician, you will use a variety of equipment in your day-to-day duties. Knowing how to use and care for the equipment available to you will contribute to a project’s and a unit’s success.
1. __________ drafting is used to show the type and proper placement of structural members in a building. A. Illustrative B. Technical C. Graphical D. Freehand 2. In the Seabees, __________ drafting specifically refers to the arrangements of machinery, utility systems, heating, air conditioning, and ventilating systems. A. Illustrative B. Technical C. Freehand D. Mechanical 3. Types of administrative drafting you may be called to perform include creating ___________. A. Technical and display charts, safety and embarkation signs, project completions, and unit readiness graphics B. Architectural, structural, electrical, and mechanical drawings C. Topographical maps, plotted profiles, and cross sections D. Portraits and landscapes 4. Charts and graphs that emphasize numerical values are called___________, while those that emphasize relations are called ___________. A. Mechanical, freehand B. Qualitative, quantitative C. Quantitative, qualitative D. Mechanical, qualitative 5. Any drafting done for or by the Navy must be prepared using the ___________. A. Latest military standard B. Department of Defense standard C. NAVFACENGCOM design manuals D. All of the above 6. ___________ is a high-grade white (or slightly tinted) transparent paper that takes pencil well and erases cleanly. A. Tracing paper B. Profile paper C. Cross-section paper D. Illustration board 3-36 7. Cross-section paper is more commonly known as ___________. A. Profile paper B. Profile/plan paper C. Graph paper D. Illustration board 8. A ___________ grade drafting pencil produces a darker, thicker line, while a ___________ grade drafting pencil produces a lighter, thinner line. A. Wooden, mechanical B. Hard, soft C. Soft, hard D. Mechanical, wooden 9. An ___________ eraser is soft and pliable and used for removing pencil or finger marks and smudges. A. Vinyl B. Art gum C. Electric D. Ruby red 10. You use a T square with the head set against the upper or lower edge of the drafting board. A. True B. False 11. A _________ consists of a long, straight strip, called the blade, which is mounted at right angles on a short strip, called the head. A. Parallel straightedge B. Steel straightedge C. Map measure D. T square 12. A _________ consists of a laminated blade with transparent plastic edges and uses a series of cords and pulleys to move up and down the drawing board. A. Parallel straightedge B. Steel straightedge C. Map measure D. T square 3-37 13. A __________ is used for drawing long, straight lines because its heavy weight helps keep it in position; it is also excellent for trimming blueprints and cutting heavy illustration board. A. Parallel straightedge B. Steel straightedge C. Map measure D. T square 14. _________ are used in combination with a T square or straightedge to draw vertical and inclined lines. A. Triangles B. Map measures C. Dividers D. Compasses 15. __________ are used for measuring and laying off angles other than those that may be drawn with a triangle or combination of triangles; they are either circular or semicircular in shape. A. Dividers B. Compasses C. Protractors D. Map measures 16. With a T square or a straightedge, you can use this drafting instrument to measure or draw any angle between 0 and 90 degrees and transfer parallel inclined lines. A. Adjustable triangle B. French curve C. Protractor D. Compass 17. ___________ are used for drawing smooth curved lines that are not arcs or circles, such as ellipses, parabolas, and spirals. A. Protractors B. Compasses C. Triangles D. French curves 18. Circles and circular curves of relatively short radius are drawn with _________. A. French curves B. Compasses C. Triangles D. T squares 3-38 19. A _________ is similar to a __________, except that both legs end in needlepoints. A. Protractor, compass B. Compass, divider C. Compass, protractor D. Divider, compass 20. _________ are used for transferring measurements from one scale to another. A. French curves B. Map measures C. Compasses D. Proportional dividers 21. The __________ of a drawing refers to the ratio between the dimensions of the graphic representation of an object and the corresponding dimensions of the object itself. A. Scale B. Topography C. Construction D. Qualitative relationship 22. ___________ scales are used wherever dimensions are measured in feet and inches. A. Engineer's B. Architect's C. Metric D. Mechanical 23. ___________ scales are used wherever dimensions are measured in 10ths. A. Engineer's B. Architect's C. Metric D. Mechanical 24. ___________ scales are used wherever dimensions are measured in meters and centimeters. A. Engineer's B. Architect's C. Metric D. Mechanical 3-39 25. ____________ are precision instruments for measuring the lengths of roads, pipelines, and other irregular outlines on maps and drawings. A. Scales B. Map measures C. Protractors D. Dividers 26. ______________ are time saving devices that are used for drawing common shapes and standard symbols and come in a wide variety of shapes. A. Protractors B. Dividers C. French curves D. Drafting templates 27. You should hold a technical fountain pen so that it is perpendicular to the drawing surface at all times to avoid uneven point wear. A. True B. False 3-40