Technical Drawing and Mechanisms

Posted on Dec 1, 2024 in Technology

Technical Drawing

Perspective

Cavalier Perspective: Two perpendicular axes create a sense of depth with a third, inclined axis.

Isometric Perspective: Axes are separated by equal angles. Piece measurements are maintained, but angles between principal axes are deformed. Parallel lines are preserved.

Drawing from Known Perspectives

Compositional Methods: Extend parallel to the relevant axis (X for vertical, Z for depth) to obtain the projected figure. Locate surfaces originating from vertices to complete missing edges and inclined planes.

Subtractive Method: Draw a rectangular prism in perspective and then “sculpt” the piece within it.

Standardization

Scales

  • Enlarged: 0:1, 5:1, 2:1, 20:1, 50:1
  • Reduction: 1:2, 1:5, 1:10, 1:20, 1:50, 1:100, 1:200, 1:500, 1:1000, 1:2000, 1:5000, 1:10000

Standard Line Types

  • Reference Line: Indicates relationships between edges.
  • Edge Line: Represents separation between planes.
  • Section Line: Indicates a break in the piece.
  • Hidden Line: Represents an edge not visible in that view.
  • Center Line: Shows the axis of a circle.
  • Symmetry Line: Indicates identical figures on both sides of the axis.
  • Sectioned Area: Indicates a section plane.
  • Cutting Plane Line: Represents a line where a cut was made.

Dimensioning

Dimensioning expresses an object’s measurements clearly on a plane.

Dimension Elements

  • Dimension Lines: Parallel to the edge being dimensioned.
  • Extension Lines: Perpendicular to the dimension line, marking the edge boundaries.
  • Leader Lines: Closed dimension lines, often with arrowheads.
  • Dimension Values: Numbers (in millimeters) indicating the actual length.
  • Symbols: Indicate special lengths or non-linear dimensions (diameter, radius, square).

Dimensioning Standards

  • Dimension elements should be thinner than the piece’s edges.
  • Uniform figures centered on dimension lines, 8mm from the object edge and 5mm from other dimension lines.
  • Do not use object edges as dimension lines.
  • Dimension only essential lengths.
  • Extension lines should not cross each other or other lines.
  • Arrows/values can extend beyond the dimension line if necessary. Use points if space is limited.
  • Extension lines should extend outside the piece unless dimensioning internal elements.
  • Angles are dimensioned with a semicircle indicating degrees.

Measuring Instruments

  • Ruler: Measures segments on paper.
  • Sewing Tape Measure: Measures curved contours and perimeters.
  • Carpenter’s Tape Measure: Measures wood pieces.
  • Tape Measure/Flexometer: Measures lengths up to 30m.
  • Caliper: Measures lengths and outer diameters with a vernier scale for precision.
  • Micrometer: Measures using a screw-nut mechanism, typically advancing 0.5mm per revolution. Calipers are more accurate than micrometers.

Mechanisms

Structures

Structures withstand loads and prevent breakage or excessive deformation.

Requirements

  • Stability: Center of gravity centered on the base.
  • Resistance: Withstand stresses without breaking.
  • Stiffness: Minimize deformation under force.

Effort is the internal stress experienced by bodies under force.

Major Efforts

  • Traction: Stretching forces.
  • Flexion: Bending forces.
  • Shear: Cutting forces.
  • Compression: Crushing forces.
  • Torsion: Twisting forces.
  • Buckling: Combined compression and bending.

Structure Types

  • Massive Structures: Use a lot of material, few holes.
  • Framed Structures: Concrete or steel rods in a grid (e.g., buildings).
  • Triangular Structures: Metal or wood bars for roofs and vertical structures.
  • Pneumatic Structures: Detachable, air pressure supports the structure.
  • Shell Structures: Thin sheets with high resistance due to curvature.
  • Domed Structures: Arches and vaults for covering large areas.
  • Suspension Structures: Cables and braces, cables resist tension.
  • Geodesic Structures: Combine vault and bar structure properties.

Structure Elements

Pillars (columns if circular, pilasters if against a wall), beams, joists, arches, voussoirs, brackets, vaults, ribs, stirrups, piles, braces.

Mechanisms

Transmit and transform forces and movements.

  • Motion Transmission Mechanisms: Transmit motion from a driving element.
  • Motion Processing Mechanisms: Convert circular to linear motion or vice versa.

Linear Transmission

Lever: F × d = R × r (Law of the Lever)

  • First Class Lever
  • Second Class Lever
  • Third Class Lever

Movable Pulley: Two pulleys, one fixed, one movable.

Hoist: Multiple fixed and movable pulleys.

Circular Transmission

Gears: Two or more wheels in contact, transmitting motion.

Belt and Pulley System: Two pulleys connected by a belt, rotating in the same direction.

Sprockets: Interlocking teeth transmit circular motion between parallel, perpendicular, or oblique shafts.

Worm Gear: Screw engages a helical gear, perpendicular axes.

Chain Drive System: Two sprockets connected by a chain.

Speed Variation

  • Drive Wheels: Multiplier, constant, reducing systems.
  • Gears: Multiplier, constant, reducing systems.
  • Belt and Pulley Train: Speed ratio depends on wheel diameters.
  • Gear Train: Speed ratio depends on the number of teeth.