Chapter Two. Layouts and Lettering

1. The observer’s eye, or station point

2. The plane of projection

3. The projectors (also called visual rays or lines of sight).

Figure 2.1 shows two drawings of a shape projected onto a plane as viewed by an observer, whose eye represents the station point. The lines projecting from the corners (or vertices) of the object are the imagined lines, called projectors.

To understand projection, imagine that the drawing is produced by points, called piercing points, where the projectors would pierce the projection plane. The drawing may be a two-dimensional representation on a sheet of paper, or it may be a two-dimensional representation shown on your computer screen, as shown in Figure 2.2, but the basic principles are the same. One reason 2D projection skills remain relevant, even with the advent of 3D modeling, is that computer monitors still display a 2D view on their flat screens.

In perspective projections, the projectors come together at the station point to form a cone, as in Figure 2.1a. Perspective drawings represent objects as we see them or as they would appear in a photograph.

In parallel projections, the projectors are parallel, as shown in Figure 2.1b.

Orthographic projections are one type of parallel projection. In orthographic (meaning right-angle) projections, the parallel projectors are perpendicular to the plane of projection. Because orthographic projections show objects in a way that their features can be represented at true size or scaled at a proportion of true size, they are especially useful in specifying the dimensions needed in technical applications.

If the projectors are parallel to each other, but are at an angle other than 90° to the plane of projection, the result is called an oblique projection.

Technical drawings of 3D objects usually use one of four standard types of projection, shown in Figure 2.3:

• Multiview

• Axonometric (includes isometric)

• Oblique

• Perspective

Multiview projection shows one or more necessary views. Either of two systems is used to arrange the views in a multiview drawing: third-angle or first-angle. You will learn about multiview projection in Chapter 6.

Axonometric, oblique, and perspective sketches are methods of showing the object pictorially in a single view. They will be discussed in Chapter 3.

The main types of projection are listed in Table 2.1.

Drawing Lines Projected drawing views use specific line patterns to represent object features. For example, when showing a 3D object, some lines represent the edges of surfaces that are hidden from that viewing direction. These hidden lines have a dashed line pattern to help the reader understand the drawing. Another type of line indicates the location of the center of a symmetrical feature, such as a hole. Familiarity with the types of lines used in technical drawings helps you read drawings and create drawings that others can easily understand.

Lettering The shapes of letters that are easy to read and write are described as part of drawing standards. Often, freehand sketching is used early in the design process to present ideas. Showing notes and information legibly helps present your ideas to others clearly. Good lettering often makes or breaks a sketch.

Measurement Systems Two measurements systems are used for technical drawings: the metric system and U.S. customary units. It is important to be familiar with both measurement systems to create and read drawings that are used worldwide.

Scale Obviously, a large item (a house or bridge for example) cannot be shown full size on a paper sheet. To clearly convey important information about particularly large or small objects, you need to select an appropriate sheet size and show drawings to scale (proportionately smaller or larger than the actual size). Standard lettering sizes for drawings depend on the sheet size.

Title Blocks Company information, the drawing scale, sheet size, and other information is included in a standard title block located in the lower right corner of the drawing to make it easy to locate these important details on every drawing layout.

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), as shown in Figure 2.4. The line gage in Figure 2.5 shows various widths.

Figure 2.6 shows freehand line technique. You may find it helpful to use 1/8″ graph paper at first to get a feel for the length of dashes used in hidden lines and centerlines. Soon you will be able to estimate the lengths by eye.

Figure 2.7 illustrates line styles for technical drawings. All lines (except construction lines) must be sharp and dark. For visible, cutting-plane, and short-break lines use thick lines. Thin drawing lines should be just as sharp and black, but only half the thickness of thick lines. Construction lines and lettering guidelines should be thin and light so that they can barely be seen at arm’s length and need not be erased. All lines should be uniform in width and darkness. Ideal lengths of the dashes used to form the line patterns are also shown in Figure 2.7.

The meter was established by the French in 1791 as the length of one ten-millionth of the distance from the Earth’s equator to the pole along the meridian that, coincidentally, passes through Paris. Since then the definition has been updated to be the distance that light travels in a vacuum in 1/299,792,458 of a second. A meter equals 39.37 inches or approximately 1.1 yards.

The metric system for linear measurement is a decimal system similar to the U.S. system of counting money. For example,

1 mm	= 1 millimeter (1{{#}}8729;1000 of a meter)
1 cm	= 1 centimeter (1{{#}}8729;100 of a meter)
	= 10 mm
1 dm	= 1 decimeter (1{{#}}8729;10 of a meter)
	= 10 cm = 100 mm
1 m	= 1 meter
	= 100 cm = 1000 mm
1 km	= 1 kilometer = 1000 m
	= 100,000 cm = 1,000,000 mm

The primary unit of measurement for engineering drawings and design in the mechanical industries is the millimeter (mm). Secondary units of measure are the meter (m) and the kilometer (km). The centimeter (cm) and the decimeter (dm) are rarely used on drawings.

Some industries have used a dual dimensioning system of millimeters and inches on drawings. However, this practice can be confusing because the sizes displayed in the two systems may contain rounding errors. If two systems are shown, the primary units are used for all manufacturing measurements, and the secondary system units (shown in parentheses or brackets) are for general information purposes only. Figure 2.10 shows a drawing using dual dimensioning. Most large manufacturers use all metric dimensions on the drawing for ease and consistency.

Dimensions that are given in U.S. customary units (inches and feet, either decimal or fractional) can be converted easily to metric values. In standard practice, the ratio 1 in. = 25.4 mm is used. Decimal-equivalents tables can be found inside the back cover, and conversion tables are also given in Appendix 30. Many handy unit conversion sites are also available on the Web at sites such as www.onlineconversion.com.

Scale is stated as a ratio of the number of drawing units to the number of actual units. For example, a machine part may be shown on a sheet at half its actual size, a scale of 1:2; a building may be drawn 1/48 of its size, a scale of 1:48 (or in U.S. customary units, 1/4″ = 1′); a map may be drawn 1/1200 actual size, a scale of 1″ = 100′ or 1:1200; or a printed circuit board may be drawn four times its size, a scale of 4:1.

SCALE: 1:2

SCALE: 1/2

SCALE: .5

For machine drawings, the scale indicates the ratio of the size of the drawn object to its actual size, regardless of the unit of measurement used. Expansion or enlargement scales are given as 2:1, 4:1; 5:1, 10:1, and so on. Figure 2.11 illustrates how the actual object relates to a drawing at half size and how that might be noted in the title block of the drawing. Figure 2.12 shows the scale for a 1 to 24 reduction noted in a title block.

Architectural drawings in the United States typically list the scale based on the number of fractions of an inch on the drawing that represent one foot on the actual object. For example, SCALE: 1/8″ = 1′.

The various scale calibrations available on the metric scale and the engineers’ scale provide almost unlimited scale ratios. Preferred metric scale ratios are 1:1; 1:2; 1:5, 1:10, 1:20, 1:50, 1:100, and 1:200.

Map scales are indicated in terms of proportions such as Scale 1:62500, fractions such as Scale 1/62500, or graphically, such as:

Engineering drawings use single-stroke sans serif letters because they are highly legible and quick to draw. (Sans serif means without serifs, or spurs.) The sans serif letters used for drawings are also referred to as Gothic. (Serif letters are sometimes called Roman, but today that term is commonly used for the upright form of the letters.) A font is the name for a set of letters with the same style. Figure 2.13 shows the distinctions among Roman, italic, serif, and sans serif fonts.

Lettering is a standard feature available in computer graphics programs. With CAD software, you can add titles, notes, and dimensioning information to a drawing. Several fonts and a variety of sizes may be selected. When modifications are required, it is easy to make lettering changes on the drawing by editing existing text.

Freehand lettering ability has little relationship to writing ability. You can learn to letter neatly even if you have terrible handwriting. There are three necessary aspects of learning to letter:

• Knowing the proportions and forms of the letters (to make good letters, you need to have a clear mental image of their correct shape)

• Spacing of letters and words for legibility

• Practice

CAD drawings typically use a Gothic (sans serif) lettering style but often use a Roman (serif) style for titles. When adding lettering to a CAD drawing, a good rule of thumb is not to use more than two fonts within the same drawing. See Figure 2.14 for a sample of the fonts available using CAD. You may want to use one font for the titles and a different font for notes and other text. Keep in mind that if you open a drawing created with software such as AutoCAD, you must have the fonts available that were used in the drawing, otherwise the software will have to substitute different fonts. This can be a problem because the horizontal spacing may be different and the text will no longer fit correctly. It may be tempting to use many different fonts in a drawing because of the wide variety available, but this tends to look distracting on the drawing. Drawings that use too many lettering styles and sizes have been jokingly referred to as having a “ransom note” lettering style.

Inclined (italic) capital letters and numerals are shown in Figure 2.18. They are similar to vertical lettering, except the slope is about 68° from the horizontal. Although you may practice hand lettering slanted at approximately this angle, it is important in CAD drawings to always set the amount of incline for the letters at the same value within a drawing so that the lettering is consistent. Inclined lowercase letters, shown in Figure 2.19, are rarely used.

Keep in mind that only one style of lettering or font, either vertical or inclined, should be used throughout a drawing.

• Never let numerals touch the fraction bar.

• Center the denominator under the numerator.

• Avoid using an inclined fraction bar, except when lettering in a narrow space, as in a parts list.

• Make the fraction bar slightly longer than the widest part of the fraction.

Dimensioning in fractions is still used in the US, but even there it is less and less common. Calculating with fractions often takes manufacturing workers extra time and errors are common. Much of the numerically-controlled manufacturing for cabinets and countertops uses millimeters as the default units, even in the United States.

Some combinations, such as LT and VA, may have to be slightly closer than other letters to look correctly spaced. In some cases, the width of a letter may be decreased slightly. For example, the lower stroke of the L may be shortened when followed by A. In typesetting, pairs of letters that need to be spaced more closely to appear correctly are called kerned pairs.

In any kind of title, give the most important words prominence by making the lettering larger, heavier, or both. Other data, such as scale and date, can be smaller. One technique for centering words in the title block when hand lettering is to roughly letter the words on a scrap of paper, slide it in the available space, and make a light mark to indicate where to begin lettering the title (Figure 2.25).

Figure 2.26 shows examples of freehand lettering at actual size.

Drawing pencils are made of graphite with a polymer binder or clay binder. They are divided into 18 grades from 9H (the hardest) to 7B (the softest) as shown in Figure 2.27. Specially formulated leads of carbon black particles in a polymer binder are also available in several grades for use on polyester film (Mylar).

Hard leads are used where accuracy is required, such as on graphical computations and charts and diagrams. For other uses, their lines are apt to be too light.

Medium leads are used for general-purpose technical drawing, such as sketching, lettering, arrowheads, and other freehand work on mechanical drawings.

Soft leads are not useful in technical drawing. They make smudged, rough lines that are hard to erase, and the lead dulls quickly. These grades are generally used for artistic drawing.

Which grade of pencil works best for you depends on your hand pressure, the humidity, and the type of paper you are using, among other things. For light lines, use a hard lead in the range of 4H to 6H. For dark lines, use a softer lead in the range of 2H to B.

Mechanical pencils are available with 0.3-, 0.5-, 0.7-, or 0.9-mm-diameter drafting leads in several grades (Figure 2.28). Their thin leads produce uniform-width lines without sharpening. The .5-mm lead is a good general size, or you can use a .7-mm lead for thick lines and .3 mm for thin lines.

However, these advantages do not eliminate the need for drawings to be easily and accurately interpreted. CAD drawings use the same general concepts and follow the same drafting standards as drawings created by hand.

Most CAD drawings are plotted on standard sheet sizes and to similar scales as hand drawings. Both CAD and hand drawings should contrast thick lines for objects with thin lines for hidden, center, and dimension lines to make the printed drawing easy to read. CAD drawings should use correct line patterns. Likewise, lettering on CAD drawings should follow these same general guidelines as for hand drawings.

One benefit of CAD is the ability to draw perfectly straight uniform lines and other geometric elements. Another is the ability to quickly represent the various styles of lines (Figure 2.30). Making changes to a CAD drawing takes about a tenth the time that it takes to edit a drawing by hand. Using CAD, you can quickly plot drawings to different scales.

Keeping CAD drawing files organized, backing up data regularly, and following conventions for naming files so that you can find them again are important considerations. Even skilled CAD users use freehand sketching, to quickly get ideas down on paper and to show their ideas on a whiteboard.

Small notebooks or sketch pads are useful when working at a site or when it is necessary to quickly record information. Many companies require bound notebooks of graph paper for recording engineering design notes so they are preserved for patent and documentation purposes. Graph paper can be helpful in making neat sketches like the one in Figure 2.31. Paper with 4, 5, 8, or 10 squares per inch is convenient for maintaining proportions.

A sketch pad of plain paper with a master grid sheet showing through underneath works well as a substitute for grid paper. You can create your own master grid sheets using CAD. Specially ruled isometric paper is available for isometric sketching, or you can use CAD to create masters.

The best drawing papers have up to 100% pure rag stock. Their strong fibers hold up well to erasing and folding, and they will not discolor or grow brittle with age. Good drafting paper should have a fine grain (or tooth) to pick up the graphite and produce clean, dense black lines. Paper that is too rough produces ragged, grainy lines, is harder to erase, and wears down pencils quickly. Look for paper that has a hard surface that will not groove too easily under pencil pressure.

Polyester film is a high-quality drafting material available in rolls and standard sized sheets. It is made by bonding a matte surface to one or both sides of a clear polyester sheet. Its transparency and printing qualities are good and it provides an excellent matte drawing surface for pencil or ink, it is easy to erase without leaving ghost marks, and it has high dimensional stability. Its resistance to cracking, bending, and tearing makes it very durable. Many companies still plot their drawings in ink on polyester film for long-term storage and reproduction.

Even large coated sheets of aluminum (which provides a good dimensional stability) have been used in the aircraft and auto industry for full-scale layouts that were scribed into the coating with a steel point rather than a pencil.

The use of the basic sheet size, 8.5″ × 11.0″ or 210 mm × 297 mm, and its multiples permits filing folded prints in standard files with or without correspondence. These sizes can be cut from standard rolls of media.

Drawing Title, Drawing Size

6 mm (.24″)

DAI

6 mm (.24″)

Drawing Number, Revision Letter

6 mm (.24″)

Section and View Letters

6 mm (.24″)

Zone Letters and Numbers

6 mm (.24″)

Drawing Block Headings

2.5 mm (.10″)

All Others

3 mm (.12″)

Name Show the name of the originating company or business (and address if desired). Refer to Figure 2.35.

Drawing Title Briefly describe the item using a singular noun or noun phrase and modifiers if necessary to distinguish it from similar items. Do not use the terms “for” or “or” in the title. For example, “Dust Cap” would be preferred over “Cap or Cover for Dust Protection,” which is too wordy.

Drawing Number Give each drawing a unique number, using the company’s numbering system.

Sheet Revision Block Track the drawing version using the number of the revision. The original release of the drawing typically shows revision 0.

Approval Block List the name(s) of the person(s) approving the drawing and the date it was approved. Additional areas of this block can be used for various design activities, if separate approval is required. For example, a company may use separate areas for structural design or manufacturing engineering approvals (Figure 2.36).

Scale List the predominant scale for the drawing. Drawings may include details at other scales, which should be noted below the detail. If the drawing is not made to a particular scale, note NONE in the scale area.

Drawing Size List the sheet size used for the drawing. This helps track the original size when the drawing is reproduced at a smaller size.

Sheet Number List the number of the sheet in the set, using whole numbers starting at 1. A format that lists this sheet out of the total number helps keep track of the entire set, for example, 1 OF 2.

DAI List the Design Activity Identification in this area when it is required. This block may be left blank or the block removed if it is not needed. Examples of DAI include: design activity name, activity name and address, and Commercial and Government Entity (CAGE) codes if applicable. CAGE codes are numbers assigned to entities that manufacture items for the government, based on the DAI.

Weight List the actual or estimated weight of the part if required (Figure 2.37).

*For more formats, title blocks, revision blocks, and materials blocks, see inside the front cover of this book.

When you are sketching, your layout may be a simple border and title strip along the bottom of the sheet (or you may be using preprinted tablets that have space to record the sketch title, date, and other pertinent data).

When creating a 2D CAD drawing, you may use a drawing template showing the sheet and border and title block, perhaps using different templates or even software interface settings for different types of drawings, such as mechanical/manufacturing, architectural, or civil.

When creating a 2D drawing from a 3D solid model, you may use a layout space that contains different viewports that allow you to show different views of the same 3D model with a border and title block.

• the size and scale of the object you will show;

• the sheet size;

• the measurement system (units) for the drawing; and

• the space necessary for standard notes and title block.

The object you are drawing is the “star” of the sketch. Keep the object near the center of the sheet. It should be boldly drawn, using thick visible lines. Make it large enough to fill most of the sheet and so that details show clearly (Figure 2.38).

You can also add details at a larger scale if necessary to show features that are smaller than the typical features of the drawing. If you add details at a different scale, label the view, for example, DETAIL A, and note the scale for the detail below it.

Architects’ Scale

Construction Lines

Decimal Inch

Decimal-Inch Scale

Drawing Lines

Drawing Number

Drawing Scale

Drawing Size

Drawing Title

Engineers’ Scale

Font

Freehand Line

Guidelines

Inclined

Italic

Kerned Pairs

Layout

Lettering

Measurement Systems

Mechanical Engineers’ Scale

Media

Multiview Projection

Name

Oblique Projection

Orthographic Projections

Parallel Projections

Perspective Projections

Piercing Points

Plane of Projection

Projectors

Roman

Sans Serif

Scale

Scales

Serif

Sheet Number

Sheet Revision Block

Sheet Sizes

Station Point

Thick Lines

Thin Lines

Title Blocks

Vertical

Weight

Zone Numbers

• Understand the basic principles of projection used in drawings.

• Demonstrate the lineweights (thickness) and types (dashed or solid) of lines used in the alphabet of lines that specify meaning in technical drawings.

• List the two main systems of measurement used on drawings.

• Use different types of scales to make measurements.

• Note the scale for a drawing in the title block. Paper drawings are scaled before they are drawn. CAD drawings are scaled when they are to be printed.

• List the advantages of several different drawing media and the qualities that distinguish them.

• Add legible and quick notes and dimensions to sketches using uppercase letters drawn by hand.

• Lay out a sheet and fill in the information in the title block using standard letter shapes.

2. What are the main advantages of polyester film as a drawing media?

3. What are the four standard types of projections?

4. Which drawing lines are thick? Which are thin? Which are very light and should not reproduce when copied?

5. What font provides the shape of standard engineering lettering?

6. Describe the characteristics of good freehand lettering.

7. Why should guidelines be used for lettering?

8. List the standard items found in a title block.

These problems are designed to fit easily on a sheet. (See the inside front cover of this book). Draw all construction lines lightly, using a hard lead (4H to 6H), and all required lines dense black with a softer lead (F to H). Draw your construction lines lightly so that they do not need to be erased.

In Exercises 2.1–2.3 you will practice measuring, and in Exercises 2.4–2.6 you will practice drawing layouts.

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Exercise 2.1 Measure the lines shown above and list their lengths using millimeters. List the inch measurements for each in square brackets [ ] to the right of the millimeter measurement.

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__________________________________________________________________________

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Exercise 2.2 Measure the lines shown above and draw them at Scale 1:2, Scale 2:1, and list their scales below them using the form Scale: X:X.

Exercise 2.3 Measure the overall interior dimensions of your room. Letter the measured length neatly in the first column as shown in the example. In the second column list how long you would draw that line at a scale of 1/4″ = 1′, third column at 3/8″ = 1′, fourth column at 1″= 1′, fifth column at 1:100 metric scale (10 mm = 1 meter).

Measurement	1{{#}}8729;4″ = 1′	3{{#}}8729;8″ = 1′	1″ =1′	1:100 Metric
10′-6″	2.625″	3.9375″	10.5″	32mm

Exercise 2.4 Create the layout for an 8.5″ × 11″ sheet as shown at right.

Exercise 2.5 Create the layout for the 210 mm × 297 mm sheet shown at right.

Exercise 2.6 Design a title block and layout for a C-size sheet. Create a name and logo for your company. Use an attractive but legible font for the titles on your layout. If assigned, design a special north arrow to be used on your drawings.

Exercise 2.7 Letter the words to your favorite song, joke, or inspirational quote of 50 words or more. Use 1/8″ tall UPPERCASE engineering lettering. Center the words near the middle of the sheet. Make sure to leave a row of space between each row of lettering. Make sure that the subject you choose is professional and appropriate.

Exercise 2.8 Lay out sheet as shown. Add vertical or inclined guidelines and fill in vertical or inclined capital letters as assigned. For decimal-inch and millimeter equivalents of given dimensions, see the inside back cover.

Exercise 2.9 Lay out sheet as shown. Add vertical or inclined guidelines and fill in vertical or inclined capital letters as assigned. For decimal-inch and millimeter equivalents of given dimensions, see the inside back cover.

Exercise 2.10 Lay out sheet as shown. Add vertical or inclined guidelines and fill in vertical or inclined lowercase letters as assigned. For decimal-inch and millimeter equivalents of given dimensions, see the inside back cover.

Exercise 2.11 Lay out sheet as shown. Add vertical or inclined guidelines and fill in vertical or inclined numerals and fractions as assigned. For decimal-inch and millimeter equivalents of given dimensions, see the inside back cover.