Technology Unit: Technical Drawings

Technology Unit - Topics

• Topics covered include Technical Drawings, Views and Projections, Constraints, Properties of Materials, Mechanical Functions, and Motion Systems.

Types of Technical Drawings

• Design plan/diagram of principles: Shows the operation of parts using forces and motion symbols.
• Technical diagram: Shows the assembly of parts. Includes parts, links, guidance symbols, and materials legend.
• Sketch: A freehand drawing with basic geometric lines.
• Cross-sectional view: Shows the internal parts of an object via slicing.
• Exploded view: Parts are pulled apart to show individual components and assembly instructions.
• Cut-away view: Shows internal parts of an object with parts sliced open.

Drafting Lines

• Geometric lines: Drawn using a ruler and compass. Used for finding the center of a circle, creating arcs and rounding corners.
• Examples of geometric constructions include finding the center of a circle and drawing rounded corners.

Basic Lines

• Visible line/contour: Thick lines defining the object's outline.
• Hidden line/contour: Medium thickness dashed lines for features not visible in the current view.
• Center line: Thin lines with small dashes within a circle or symmetrical shape to represent the center.
• Extension line: Thin lines extending from a dimension point to show dimension.
• Dimension line: Thin lines with dimensions placed on object.
• Leader line: Thin lines connecting dimension and a part of the object that is being measured.
• Hatching line: Thin slanted lines evenly spaced to represent a material's surface in a sectional view.
• Cutting plane line: Thick lines with arrowheads showing the plane of sectional view.

Scaling

• Scaling is reducing or enlarging a drawing to represent its actual size using a ratio (drawing:actual).
• The actual size drawing has a ratio of 1:1.
• Scale reduction has a ratio of 1:2.
• Scale enlargement has a ratio of 2:1.

Dimensioning

• Dimensioning uses lines to indicate actual lengths, widths, heights, depths, and diameters of parts.
• Dimensions can be placed inside or outside of the drawing but should not overlap.

Practice Questions

• Practice problems are provided for each topic.

Projections

• Orthogonal projection: Light rays are perpendicular to the plane of the paper, creating multiple views that define a 3-D object.
• Multiview: Top, bottom, front, right & left side views.
• Isometric: Three-dimensional view; angles of 30° with the edges of the object.
• Oblique: One face of the object will face the view.

Constraints

• Constraint is a force imposed on a material resulting from external forces.
• Types of Constraints: Compression, Tension, Torsion, Deflection, and Shear.
• Examples of Constraints: crushing a can, squeezing a sponge, etc.

Properties

• Properties of materials determine resistance to constraints.
• Properties like hardness, ductility, malleability, elastic and resilience are characteristics of materials.

Materials (Metals & Alloys, Wood, etc.).

• Materials like metals and alloys, wood, plastics, ceramics, and composites are grouped by their main properties.
• Examples of Metals & Alloys: Iron, Aluminum, Copper, Steel, Plastic, wood.

Mechanical Systems

• Mechanical function: Movement or motion of objects or their components.
• Types of motion: Translation (rectilinear movement), rotation, and helical movement (combination of rotation and translation).
• Examples of mechanical functions: gluing, linking, guiding, sealing, lubricating
• Types of links: Fixed, Rotating, Sliding, Sliding-Rotating, Spherical, Spiral

Motion Systems

• Motion types: transmission and transformation.
• Transmission: Same type of motion is relayed from the driving part to the driven part.
• Transformation: Different types of motion are relayed from driving component to driven component.
• Components of motion systems: Driver, Driven, Intermediate (used in some systems)