इंजीनियरिंग ड्राइंग मूल बातें

• Engineering drawings communicate designs precisely and unambiguously.
• They adhere to standardized conventions for lines, symbols, and dimensioning.
• These standards ensure that engineers, designers, and manufacturers can accurately interpret the drawing.

Drawing Instruments and Materials

• Drawing boards provide a stable, flat surface for creating drawings.
• T-squares are used to draw horizontal lines and provide a reference for setting angles.
• Set squares (triangles) are used to draw lines at specific angles (e.g., 30, 45, 60, and 90 degrees).
• Compasses are used to draw circles and arcs.
• Dividers are used to transfer measurements and divide lines into equal segments.
• Scales are used to accurately measure and transfer dimensions.
• Pencils with varying hardness (e.g., H, HB, 2H) are used for different line types and drawing purposes.
• Erasers are used to remove unwanted lines and marks.
• Drafting tape is used to secure the drawing sheet to the drawing board.
• French curves are used to draw irregular curves.

Lines and Lettering

• Visible lines (continuous thick lines) represent the visible edges and outlines of an object.
• Hidden lines (dashed lines) represent edges and surfaces that are hidden from view.
• Center lines (long-short dashed lines) indicate the center of circles, arcs, and symmetrical features.
• Dimension lines (thin lines with arrowheads) indicate the extent of a dimension.
• Extension lines (thin lines) extend from the object to the dimension lines.
• Section lines (hatch lines) indicate the area that has been cut in a section view.
• Lettering should be clear, legible, and conform to standardized styles (e.g., uppercase Gothic).
• The height of lettering should be consistent throughout the drawing.

Geometric Constructions

• Bisecting a line: Dividing a line into two equal parts.
• Bisecting an angle: Dividing an angle into two equal angles.
• Drawing parallel lines: Creating lines that are equidistant from each other.
• Drawing perpendicular lines: Creating lines that intersect at a 90-degree angle.
• Dividing a line into equal parts: Dividing a line into a specified number of equal segments.
• Constructing polygons (e.g., triangles, squares, pentagons, hexagons): Drawing polygons with specific dimensions and angles.
• Constructing tangents to circles: Drawing lines that touch a circle at only one point.

Orthographic Projections

• Orthographic projection is a method of representing a 3D object in 2D using multiple views.
• The most common views are the front view, top view, and right-side view.
• Each view shows the object as seen from a different direction, with all projection lines perpendicular to the projection plane.
• The front view typically shows the most important features of the object.
• The top view shows the object as seen from above.
• The right-side view shows the object as seen from the right.
• Hidden lines are used to represent features that are not visible in a particular view.

Isometric Projections

• Isometric projection is a type of pictorial projection in which all three axes are equally foreshortened.
• All three axes are drawn at 120 degrees to each other.
• Isometric drawings are easy to create and visualize, but they do not accurately represent the true proportions of the object.
• Isometric lines are lines that are parallel to one of the three isometric axes.
• Non-isometric lines are lines that are not parallel to any of the isometric axes.

Sectional Views

• Sectional views are used to reveal the internal features of an object.
• A cutting plane line indicates the location of the imaginary cut.
• Section lines (hatch lines) indicate the area that has been cut.
• Different materials are represented by different section line patterns.
• Full sections: The cutting plane passes entirely through the object.
• Half sections: The cutting plane passes halfway through the object.
• Offset sections: The cutting plane is bent to pass through important features.
• Removed sections: The section view is drawn separately from the main view.

Auxiliary Views

• Auxiliary views are used to show the true shape of inclined surfaces.
• A primary auxiliary view is projected directly from one of the principal views.
• A secondary auxiliary view is projected from a primary auxiliary view.
• Auxiliary views are necessary when the inclined surface is not parallel to any of the principal projection planes.

Dimensioning

• Dimensioning is the process of adding measurements to a drawing to specify the size and location of features.
• Dimensions should be clear, concise, and complete.
• Dimensions should be placed outside the object whenever possible.
• Dimension lines should be thin and have arrowheads at both ends.
• Extension lines should extend from the object to the dimension lines.
• Leaders are used to connect notes or dimensions to specific features.

Dimensioning Techniques

• Chain dimensioning: Dimensions are placed in a continuous line from one feature to the next.
• Parallel dimensioning: Dimensions are placed parallel to each other, starting from a common datum.
• Datum dimensioning: Dimensions are referenced from a common datum (reference point or surface).
• Coordinate dimensioning: Dimensions are specified using coordinates (e.g., X, Y, Z).
• Angular dimensioning: Dimensions are used to specify angles.
• Diameter dimensioning: Dimensions are used to specify the diameter of circles.
• Radius dimensioning: Dimensions are used to specify the radius of arcs and fillets.

Tolerances

• Tolerance is the permissible variation in a dimension.
• Tolerances are specified to ensure that parts will fit together and function properly.
• General tolerances: Tolerances that apply to all dimensions on the drawing, unless otherwise specified.
• Specific tolerances: Tolerances that apply to specific dimensions.
• Limit dimensions: The maximum and minimum permissible values for a dimension.
• Unilateral tolerance: The variation is allowed in only one direction (either positive or negative).
• Bilateral tolerance: The variation is allowed in both directions (positive and negative).
• Geometric Dimensioning and Tolerancing (GD&T): A system of specifying tolerances based on the function of the part.

Fasteners and Standard Parts

• Standard parts (e.g., bolts, nuts, screws, washers, rivets) are commonly used in engineering designs.
• These parts are manufactured to standardized dimensions and specifications.
• Drawings of standard parts should include the necessary information to identify the part (e.g., size, material, thread type).
• Simplified representations of fasteners are often used in assembly drawings.

Assembly Drawings

• Assembly drawings show how the individual parts of a product fit together.
• They typically include a bill of materials (BOM) that lists all the parts used in the assembly.
• Assembly drawings may also include exploded views, which show the parts separated from each other to illustrate their relative positions.
• Balloons or item numbers are used to identify each part in the assembly drawing.

Computer-Aided Design (CAD)

• CAD software is used to create and modify engineering drawings electronically.
• CAD offers many advantages over manual drafting, including increased accuracy, speed, and flexibility.
• 2D CAD software is used to create 2D drawings, while 3D CAD software is used to create 3D models.
• CAD files can be easily shared and modified, facilitating collaboration among engineers, designers, and manufacturers.
• CAD software also allows for the creation of realistic renderings and animations.