The texts that appear on technical drawings are used to communicate non-graphic information and may be as highly important as graphic information. Without text and lettering, it would be almost impossible to describe technical drawings completely.
The fact that lettering or lettered text must always be used to completely express and describe the details of an object goes to show just how essential it is for all types of technical drawing.
Definition of lettering in technical drawing
Lettering is the act or process of creating, inscribing, or writing letters, titles, subtitles, numbers, notes, fractions, decimal points, symbols, dimension values, equations, and other important non-graphic information to express or illustrate details of objects or items on drawings. Lettering describes and provides detailed information about each particular drawing: instructions, the size, dimensions, notes, etc.
Lettering can also be defined as any writing process that expresses the details of objects or items on drawing paper by the use of lettered texts in the form of alphabets, numbers, fractions, and/or decimal points which could also provide detailed specifications for objects.
Common types of lettering in technical drawing
There are two broad or common classes of lettering: traditional and computer-aided design/drafting (CADD) lettering; implying that lettering can be done by hand or computer.
Traditional or hand lettering is of two types: free hand lettering and mechanical lettering; while CADD on the other hand could actually be more than the 12 lettering types listed in this post, along with images.
1. Traditional lettering
(i) Free hand lettering
Drawing and lettering all started with the hand before evolving into the widely used CADD lettering of today. Although free hand lettering is used much less nowadays, it is still important to master how to write clear, legible, and comprehensible hand-lettered words, numbers, and decimal points that conform to universally accepted or standard styles.
Lettering can be done with the hand by using “guide lines” which are very light or thin construction lines that serve as guides to create clear and uniform letters on technical drawings. Hard pencils, such as 4H, 5H, or 6H, are often used to construct guide lines from a lettering guide, as shown in Figure 1.
Figure 1: Adjustable lettering guide for creating guide lines and applying hand lettering in technical drawings (Source: Technical Graphics Communication, 4th edition, page 285)
Lettering guides help to conveniently set out text dimensions and inclinations or orientations, and can be used to create vertical, horizontal, or inclined guide lines. The individual letters are drawn within these guide lines.
Each letter is constructed via a particular style. Figure 2 shows examples of different capital or uppercase letters and numbers in vertical format, while Figure 3 shows examples of different lowercase letters in vertical format.
Figure 2: Capital or uppercase letters and numbers in vertical format (Source: Technical Drawing with Engineering Graphics, 15th edition, page 41)
Figure 3: Lowercase letters in vertical format (Source: Technical Drawing with Engineering Graphics, 15th edition, page 41)
(ii) Mechanical lettering
All text in traditional drawings was hand lettered and very personalized until Johann Gutenberg invented printing in the 15th century; but with the invention of printing, the text styles used for lettering in technical drawing became more standardized.
Mechanical lettering guides—such as the lettering template shown in Figure 4, the press-on type, and the lettering machine—were all developed in the years that preceded CADD.
Figure 4: Mechanical lettering guide or template for traditional or hand lettering in technical drawing
2. Computer-aided design/drafting (CADD) lettering
Computer-aided design/drafting has provided users with many text style options and almost eliminated any need for hand lettering. One of the greatest advantages that CADD lettering and tools have over traditional lettering and tools is their remarkable speed and also the speed with which text lettering can be done on technical drawings.
CADD text is grouped and classified according to different characteristics. The style and size of a CADD text type define its font, but the text can vary if bold or italic versions are applied during lettering on a technical drawing. Figure 5 shows the characteristics of a CADD text type. It is important to note that the type size of CADD texts is measured in “points” and each vertical inch consists of 72 points; therefore, a 36-point type CADD text is about ½ inch high.
Figure 5: Important terms associated with each available CADD text or interface (Source: Technical Graphics Communication, 4th edition, page 287)
Three major classes of CADD lettering: (A) Alphabets/letters, (B) Numbers and fractions, and (C) Decimals
(A) Lettering of alphabets/letters: 12 types
(i) Sans serif lettering
A Sans serif typeface is a typeface that does not have any serifs, spurs, or sharply pointed projection. For example, the old school and popular Gothic typeface is a sans serif letter or typeface. The Sans serif letters used in technical drawings are also referred to as Gothic text.
Figure 6: Sans serif lettering using CADD (Source: Technical Drawing with Engineering Graphics, 15th edition, page 40)
(ii) Serif lettering
A serif is a spur, small finishing stroke, sharply pointed projection) that is at right angles to the main character stroke of the CADD typeface.
Figure 7: Serif lettering using CADD (Source: Technical Drawing with Engineering Graphics, 15th edition, page 40)
(iii) Roman lettering
Figure 8: Roman lettering using CADD (Source: Technical Drawing with Engineering Graphics, 15th edition, page 40)
(iv) Italic letters/lettering
Figure 9: Italic letters/lettering using CADD (Source: Technical Drawing with Engineering Graphics, 15th edition, page 40)
(v, vi, vii, viii, ix, x, xi, and xii) Seven other different lettering using CADD: AutoCAD Txt Font, Roman Simplex, Roman Duplex, Baskerville, Times New Roman, Playbill, Arial, and Letter Gothic:
Figure 10: Seven other different lettering types using CADD (Source: Technical Drawing with Engineering Graphics, 15th edition, page 40)
(B) Lettering of numbers and fractions
When indicating a fraction on a technical drawing, the number in the fraction should be the same size as any other number on the drawing. The height of a fraction should be twice the height of its corresponding whole numbers, and both the numerator and denominator should be about three-fourths as high as the whole number so there can be sufficient space between both of them and the fraction bar which can also be placed diagonally, depending on company or school standards.
Figure 11: Lettering of fractions using CADD (Source: Technical Drawing with Engineering Graphics, 15th edition, page 43)
Figure 12: Lettering options for fractions using CADD (Source: Engineering Drawing and Design by David A. Madsen, page 196)
(C) Lettering of decimal points
When lettering any dimension value that has a decimal point, the decimal point should be uniform, dense, and large enough for viewers to see, and it should be placed in line with the bottom edge of the text.
Whenever any metric or millimeter dimension is less than 1, a zero should be placed before the decimal point; for example, 0.5. But, whenever an inch dimension is less than 1, a zero should not be placed before the decimal point; for example, .02.
Whenever a metric dimension consists of only whole numbers, neither a decimal point nor a zero should be indicated; for example 24, instead of 24.0.
Figure 13: Lettering options for decimal points using CADD (Source: Engineering Drawing and Design by David A. Madsen, page 195)
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