Technology Unit: Technical Drawings Overview

Technology Unit Topics

• Technical drawings, views and projections, constraints, properties, materials, mechanical functions, and motion systems are covered.

Types of Technical Drawings

• Design plan/diagram of principles: Shows the name of parts, forces, and motion symbols, illustrating the operation.
• Technical diagram: Includes names of parts, links, guidance symbols, and a legend for materials, representing the assembly.
• Sketch: Freehand drawing with basic geometric lines.
• Cross-sectional view: View of an object sliced to show internal parts, useful for anatomy-based diagrams.
• Exploded view: A projection showing parts separated, often with labeled and numbered parts, with assembly instructions.

Drafting Lines: Geometric Lines

• Finding the centre of a circle by intersecting centre lines.
• Drawing arcs using a compass between lines.
• Drawing rounding of a corner, as shown in a table diagram. Examples of rounding using compass show a "no rounded corner" example, and a "rounded using an arc".

Basic Lines

• Visible line/contour: Thick line for outlines or contours.
• Hidden line/contour: Medium thickness dashed line for hidden contours.
• Center line: Fine line with a small dash in the center for symmetrical shapes or circles.
• Extension line: Fine line for dimensions.
• Dimension line: Fine lines showing measurements of parts, always in mm.
• Leader line: Fine line pointing to a dimension with the corresponding measurement.
• Hatching: Slanted, equally-spaced lines used to display a section of the object.
• Cutting plane: Thick line with arrow ends. Indicates the place of a cross-section.

Scaling

• Reduced or enlarged scale representation of actual size is written as a ratio (drawing:actual).
• Examples of actual size, scale reduction, and scale enlargement are shown, along with practice questions requiring students to determine the scale for objects given measurements.

Dimensioning

• Dimensioning shows the real-life size, width, height, depth, and diameter of parts of an object.
• The dimensions can be placed inside or outside the drawing, depending on clarity.
• Example of a skateboard drawing displays example dimensioning.
• There are practice questions for example diagrams showing deodorant sticks.

Projections: 2-D Representation of a 3-D Object

• Orthogonal projection: Light rays are perpendicular to the paper plane.
• Multiview projection: Shows multiple orthographic views (top, front, side) of an object.
• Isometric projection: Light rays are perpendicular to the paper plane and have an equal angle to the drawing plane.
• Oblique projection: The object is angled, allowing one face to be parallel to the drawing plane; but depth is drawn at an oblique angle.

Constraints

• Constraint: A stress or force on a material due to external forces.
• Types: Compression, tension, torsion, deflection (bending), shearing.
• Examples: Crushing a can, squeezing a sponge, tug of war, etc. There are practice questions where students need to identify the constraint in given diagrams.

Properties

• Material properties: Hardness, ductility, malleability, elasticity, resilience, stiffness/rigidity, brittleness, electrical/thermal conductivity/insulators, and corrosion resistance; are key factors in material selection.
• Materials: Metals and alloys, wood, plastic, ceramics, glass, composites (reinforced matrix), are categorized.
• Corrosion resistance: Metals like nickel, aluminum, and chrome are often more corrosion-resistant.

Mechanical Systems and Types of Motion

• Mechanical systems: Systems of component parts moving in various ways.
• Translation: Motion in a straight line.
• Rotation: Motion in a circular or revolving manner.
• Helical: A spiral movement.
• Motion symbols are included, illustrating the types and their directions.

Types of Links

• Fixed link: No movement.
• Rotating link: Rotation.
• Sliding link: Translation.
• Sliding-rotating link: Translation followed by rotation.
• Spherical link: Rotation in multiple directions.
• Spiral link: Helical.
• Characteristics like direct or indirect linking, rigid or flexible (elastic), removable or non-removable, and complete or partial links are covered.

Guiding

• Guiding controls: Direct the moving parts by controlling their movement during operation.
• Types: Translational, rotational, and helical.
• Examples: Tracks, grooves, axles, cylinders, and threads are examples of guiding controls
• Practice Questions are included, looking at guiding components in various systems.

Motion Systems

• Motion transmission: The same type of movement.
• Motion transformation: Different types of movements.
• Driver: The part that receives the force.
• Intermediate: The connecting part(s) between the driver and the driven.
• Driven: Driven component receives the motion.

Motion Transmission Systems

• Gear trains, friction gears, worm and worm gears, belt and pulley systems, chain and sprockets.
• Reversibility of movement and speed changes are considered.

Motion Transformation Systems

• Different types of motions like rack and pinion, screw gears, cam and followers, connecting rod and crank, and slider crank systems are included
• Practice questions on the systems are included.