Engineering Drawings: Lettering

• The most important requirement for lettering in engineering drawings is legibility, ease, and rapidity.

Evolution of engineering letters

• Egyptian
• Phoenician
• Greeks
• Romans

Importance of Letters on Engineering Drawings

• Provides additional information that regular drawings can't show
• Forms the written language of industry
• Records ideas
• Helps transmit ideas

Letter Styles

• Gothic: Plain and legible with strokes of even width
• Roman: Thin and thick strokes that terminate with a serif
• Text/Old English: Ornamented, decorative, and used for commercial purposes

General Proportions of Letters

• Normal: Used when there is ample space, not too wide nor too narrow

• Compressed: Width is narrower than normal

• Extended: Used when the space is wide, wider than normal

• Lightface Letters have thin stems

• Boldface Letters have thick stems

Uniformity in Lettering

• Height
• Proportion
• Inclination
• Line strength
• Spacing of letters and words

Rule of Stability

• Letters BEXKSZ and numbers 358 are drawn smaller at the top than at the bottom
• Applies to capital letters only

Width Categorization of Uppercase Letters

• Narrowest: I
• Widest: W
• Square: TOMQ VAXY
• Slightly Narrower Than Square: BCDEFGHJLNPSRUZ

Lettering Techniques

• Knowledge of the correct formation, forms, and order of strokes.
• Knowledge of Composition-Spacing of letters and words.
• Practice continuously with effort to improve.

Classification of Guidelines

• Horizontal: Regulate the height of letters
• Vertical or Inclined: Keep letters uniformly vertical or inclined
• Ascender shows the small letter NA NAKA LAWIT SA TAAS
• Descender shows SA BABA

Guidelines for Uppercase Letters

• Cap line
• Baseline

Guidelines for Combination of Upper and Lowercase Letters

• Cap line
• Waist line
• Baseline
• Drop line

Basic Equipment Used in Engineering Drawings

• Drawing board: A table top on which the work is fastened
• T-Square: Used for horizontal lines, to aid triangles for vertical and inclined lines
• The main parts are the head, body, and blade which consist of the working edge and the false edge
• Celluloid straight edge is preferred for the blade
• Triangles: 45x45x90 degrees and the 30x60x90 triangles used, the base is held against the working edge.
• Celluloid triangles are preferred and should be kept flat when not in use.

Instruments and Their Uses in Engineering Drawings

• Dividers: Dividing distances into equal parts and transferring measurements
• Compasses: Drawing arcs and circles larger than 1" diameter
• Protractor: Measuring or setting off angles
• Drawing Ink: Composed of carbon in colloidal suspension and gum, carbon provides black color and gum waterproofs and quickens drying.
• French/Irregular Curve: Drawing curves with a non-constant radius
• Scales: Laying out distances and making measurements
• Common scales: Architect, mechanical, and civil engineer's scales
• Templates: Used to draw shapes of detail
• Drafting Tape: Attaching paper to the drawing board

Lines

• Line: Path of a moving point
• Straight Line: Shortest distance between two points
• Horizontal: Level, parallel with the horizon, drawn from left to right
• Vertical: Parallel to the plumb line, perpendicular to horizontal
• Inclined: Neither horizontal nor parallel
• Parallel: Equal distance apart
• Perpendicular: Right angles to each other
• Intersecting: Lines that meet at an angle
• Curved: No straight part
• All straight lines are right lines
• Mixed: Combination of curved and straight
• Measuring: Reference line where we layout measurements.
• Construction: Light pencil lines that aid in creating required lines
• Circle: Closed curve equidistant to a center point
• Arc: Part of a circle
• Tangent: Touching without cutting a line or arc
• Concentric Circles: Circles drawn with one common center
• Eccentric Circles: Circles drawn with different centers
• Center: Alternating long and short dashes

Engineering Geometry

• Deals with proficiency in geometrical construction and practical application of geometry principles
• Line: Geometrical figure made by a point's movement, length without width or thickness.
• Point: Represents a location in space or drawing, no width, height, or depth.
• Arc: Portion of a circle's circumference
• Circle: Plane figure bounded by a circumference, every point equidistant to the center
• Bisect: Divide into two equal parts
• Triangle: Bounded by three straight lines
• Quadrilateral: Bounded by four straight lines
• Square: Equal sides with right angles.
• Rectangle: Opposite equal sides with right angles.
• Tangent: Touches a circle at a point on the circumference without cutting.
• Ellipse: Plane curve formed by a point such that the sum of its distances from two foci is constant, equal to the major axis.
• Parabola: Curve generated by a point equidistant from a fixed point (focus) and a directrix.
• Involute: Spiral curve made by a point on a taut string unwinding from a shape.
• Archimedes Spiral: Curve generated when a point moves from another point, its distance increasing uniformly with the angle.

Geometry Terms Related to Lines and Angles

• Angle: Space/difference between intersecting lines
• Acute Angle: Less than 90 degrees
• Obtuse Angle: More than 90 degrees
• Chord: Straight line connecting two circumference points
• Isosceles Triangle: Two equal sides and angles
• Scalene Triangle: No equal sides or angles
• Equilateral Triangle: Equal sides and angles
• Right Angle: 90 degrees.
• Concentric Circle: Circles with a common center
• Eccentric Circle: Circles inside an outer circle with different centers
• Regular Polygons: Plane figure, equal straight sides
• Perpendicular Lines: Intersecting lines forming a right angle (90 degrees)
• Parallel Lines: Never meet
• Radius: Shortest distance from circumference to the center
• Circumference: Bounding length of a circle