Technical lettering


Technical lettering

Technical lettering is the process of forming letters, numerals, and other characters in technical drawing. It is used to describe, or provide detailed specifications for, an object. With the goals of legibility and uniformity, styles are standardized and lettering ability has little relationship to normal writing ability.

Contents

Introduction

Engineering Graphics is said to be Engineers' language. In every language there are two primary requirements viz. Grammar and Lettering. So Technical Lettering is indeed required while learning the concepts of Engineering Graphics, Machine Drawing, Machine Design and all.
Engineering drawings use a Gothic sans-serif script, formed by a series of short strokes. Lower case letters are rare in most drawings of machines.

Methods of forming letters

  1. Freehand lettering is done without the assistance of tools. To regulate lettering height, commonly 3 mm (1/8"), guidelines are drawn.
  2. Mechanical lettering is done using tools such as lettering guides, templates, or using a small mechanical pantograph referred to by the Keuffel & Esser trademark "Leroy"
  3. Modern drawings are lettered with computer-aided design software.

Freehand Lettering

Technical Lettering

For quick action in work, it is required to have practice of freehand lettering as it allows to represent ideas in a short time and in a more efficient manner. Freehand lettering is as shown in the adjacent image.In freehand lettering, the two basic things are generally followed:
The letters to be drawn, though freehanded, should be stable and graceful. In some cases the stability may get damaged. (As in case of P and F, which show a Top-Heavy effect. But it is still unavoidable.) In other cases the stability and the grace of the letters may be maintained by either
1.Drawing the lower parts of the letters like B,E etc. wider than the upper parts
or
2. Drawing the horizontal line at the center of these letters just above their geometric axis.(Exception: In case of the letter A, the horizontal member is drawn below geometric center axis. Here along with stability one more factor is considered that is equality of areas below and above the center line. If a horizontal line is drawn exactly at the center, then the difference in the areas of the triangle above the line and the trapezium below the line is much larger. This creates an unusual effect to our eyes.)
* When the combination of letters occures then it should be kept in mind that we are writing a whole word not a single letter. Hence emphasis should be on the overall beauty of the word rather than one or two letters.
The GOTHIC is the most common lettering font used in freehand lettering. The reason behind this is, the width of each line element of each letter is same throughout. Either STRAIGHT GOTHIC or INCLINED GOTHIC maybe used for lettering. The angle of inclination of the letters in INCLINED GOTHIC is 15° with respect to the vertical.Vertical lines are usually drawn in an upward direction. However, drawing a number of vertical lines or lines slanted in thesame direction, the way of drawing them will begoverned.Vertical lines should be drawn with greatest control.

Mechanical Lettering

In Mechanical Lettering, standard uniform characters that are executed with a special pen held in a scriber and guided by a template. Mechanical lettering does not normally require the use of lettering guidelines. You will use mechanical lettering principally for title blocks and notes on drawings, marginal data for special maps, briefing charts, display charts, graphs, titles on photographs, signs, and any other time that clear, legible, standardized lettering is required. One of the most popular types of mechanical lettering sets is the LEROY lettering set.
The Mechanical Lettering is some times done using special type of device called a Pantograph.
A PANTOGRAPH is basically a device comprising of four links which are pinned to each other in a parallelogram fashion. The links can move about the hinge. The lowermost link of the parallelogram is fixed to two rigid supports. One vertical link at one end is connected to a profile tracer which traces the profile of the letter to be drawn and the second vertical link and the other horizontal link are jointly connected to a pencil that draws the exact shape of the profile traced.

Dimensions of Letters

  • A detail drawing such as giving shape of a part,furnish of part, location of hole, kind of finish, type of material, number required etc. all such information on a drawing is done by use of lines, symbols, figures, and notes and all this is consist of dimensioning. And this lines, symbol language in machine drawing is known as technical lettering.
  • The Nominal Size of lettering is defined by the height (h) of the outline contour of the upper-case (capital).
  • Central Line is the imaginary line in the middle of each line or line element which is a constitutive part of a graphic character set.
  • If we consider d as the width of the line element and h as the height of the line element, then the two standard ratios for d/h are: 1/14 and 1/10, which are feasible because they result in a minimum number of line thicknesses.
  • Location of Central Lines- The nominal size (h) and the spacing between characters (a) shall be taken as the basis for defining the central line.
  • Range of Nominal Sizes -The range of nominal sizes are 2.5 mm ;3.5mm ; 5 mm; 7 mm; 10 mm; 14 mm; 20 mm;

The multiple of 1.414(square root of 2) is the range of heights for lettering is derived from the standardized progression of dimensions for paper sizes.

  • Lettering Angle-The lettering may be vertical (upright) or inclined (sloped) to the right at 75° from the horizontal.
  • The spacing between two characters may be reduced by half, if this gives a better visual effect.
  • various letters are divided into no. of parts so that dimensions will be accurate.
    Dimensioning of Letters
  • The size of letter is described by its height. According to thr height of letters, they are classified as :
  1. Lettering A
  2. Lettering B

Lettering A

Characteristic Parameter Ratio Dimensions(mm)
Lettering Height
(Height of capitals)
h (14/14)h 2.5 3.5 5 7 10 14 20
Height of lower case letters
(without stem or tail)
c (10/14)h - 2.5 3.5 5 7 10 14
Spacing between characters a (2/14)h 0.35 0.5 0.7 1 1.4 2 2.8
Minimum spacing of base characters b (20/14)h 3.5 5 7 10 14 20 28
Minimum spacing between words e (6/14)h 1.05 1.5 2.1 3 4.2 6 8.4
Thickness of lines d (1/14)h 0.18 0.25 0.35 0.5 0.7 1 1.4

Lettering B

Characteristic Parameter Ratio Dimensions(mm)
Lettering Height
(Height of capitals)
h (10/10)h 2.5 3.5 5 7 10 14 20
Height of lower case letters
(without stem or tail)
c (7/10)h - 2.5 3.5 5 7 10 14
Spacing between characters a (2/10)h 0.5 0.7 1 1.4 2 2.8 4
Minimum spacing of base characters b (14/10)h 3.5 5 7 10 14 20 28
Minimum spacing between words e (6/10)h 1.5 2.1 3 4.2 6 8.4 12
Thickness of lines d (1/10)h 0.25 0.35 0.5 0.7 1 1.4 2

References


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