School of Technology

TECH 13580 - Engineering Graphics I

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Developments are a type of drawing associated with the creation of patterns, usually in sheet metal. Unfolding a cardboard box reveals its development. A closely related topic, intersections, involves the location and shapes of openings on a development caused by the intersection of various geometric forms, such as a chimney opening on a house roof. People employed in the heating, ventilation, and air conditioning trades must be highly skilled with the ability to create intricate developments. Often developments are drawn or scribed on the actual material, such as sheet metal. Developments can also be made on paper or corrugated paper to serve as templates. Typically developments are full scale and usually not dimensioned. Sometimes half developments are drawn for symmetric objects to save time which then requires the drawing be flipped over to scribe the mirrored other half.

EXAMPLES 

sketch of Prism sketch of Cylinder sketch of Pyramid sketch of Cone

Stretch-out Line a horizontal straight across from the bottom of the front view upon which the development is " stretched out ". 

Fold Lines lines within the development's outline to indicate the object's folds or creases.

Foreshortened Lines any lines on a drawing which are not true-length, and thus inaccurate, when each end is not  the same distance from the plane of projection, i.e., a sloping line

Chordal Error the use of a chord to represent a curved surface,  " the shortest distance between two points", minimized by dividing the top view by smaller angles ( 15 degrees rather than 30 degrees )

Elements lines within a curved development for measurement purposes, not as a fold, infinite number possible

Truncation when a cone is cut off at an angle 

Frustum when a cone is cut parallel to its base 

Transition Pieces sheet metal connection between different forms, common with furnace pipes 

Hems & Joints 

Parallel-line Method when the sides of the object are perpendicular to the base ( vertical sides ) , uses a straight stretch-out line, height projected from front view & length transferred from top view 

Radial-line Method when the sides of the object slope toward the apex, common to cones and transition pieces, stretch-out line not straight, concern for finding true length 

Triangulation Method associated with radial method to find true length, essentially the rotation of a point to locate to locate both ends of a line equidistant from the plane of projection