Fundamentals of Technical Drawing and Projection Systems

The Dihedral System and Orthogonal Projection

The Dihedral System is a method for representing an object by its orthogonal projections onto perpendicular planes.

Elements of the Dihedral System

• Projection Planes: These are perpendicular, typically consisting of a vertical plane and a horizontal plane.
• Ground Line (Land Line): The intersection between the vertical and horizontal planes.

Representation of Solids and Standard Views

The system facilitates the representation of solids using standard views (projections):

• Elevation (Front View)
• Ground (Plan View)
• Right Profile
• Left Profile
• Rear Elevation

Axonometric Projection Systems

Axonometric projection projects bodies from three-dimensional space onto a plane, often called the picture plane, providing a volumetric appearance of the body.

Cylindrical Orthogonal Projection

In this method, the angles between the axes define the type of projection:

• Isometric Projection: Axes are separated by 120°.
• Dimetric Projection: Two axes form equal angles, and the third is unequal.
• Trimetric Projection: All three axes form unequal angles.

Oblique Cylindrical Projection

• Cavalier Perspective: The projection axes are typically set at 90 degrees relative to the picture plane.

Conic (Linear) Perspective

Conic perspective drawing of objects and spaces allows simulating the perception of volume and depth that the human eye appreciates.

Key Elements of Conic Perspective

• Picture Plane
• Viewpoint
• Geometral Plane (Ground Plane)
• Plane of the Horizon
• Horizontal Line
• Ground Line (Land Line)
• Visual Focal Point
• Vanishing Points

Types of Conic Perspective

• Front Perspective: The solid has one face parallel to the picture plane.
• Oblique Perspective: The solid has no face parallel to the picture plane.

Standardization in Technical Drawing

Standardization is the set of specific rules and regulations that define the dimensions and qualities of products and technical documentation.

The primary objective of standardization is to simplify, unify, and specify information to prevent misidentification of objects and models.

Standardized Elements

• Lines: The thickness and characteristics of the lines used are standardized.
• Formats: Paper sizes (e.g., A4, A3) are standardized.
• Labeling and Annotation: Writing the necessary information on a design must adhere to standardized practices.

Scale and Dimensioning

Scale Definition and Types

Scale is the ratio of similarity established between the measures of the drawing and the actual object represented.

Types of Scale

• Natural Scale (1:1): The drawing and the real object have the same extent.
• Enlargement Scale: The drawing is greater than the real object.
• Reduction Scale: The drawing is smaller than the real object.

Dimensioning (Quotation)

Dimensioning is the process of reflecting, using lines and numbers on a drawing, the actual dimensions of an object and its parts.

Elements of Dimensioning

• Auxiliary Dimension Lines
• Dimension Lines
• Dimension Numbers