Chapter 23 Developments and Intersections

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Engineering Drawing and Design
Sixth Edition
Chapter 23
Developments and Intersections
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23-1 Surface Developments

• Sheet-metal development
• Straight-line development

PhotoDisk
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Surface Developments

• Surface development Creating an object by
  folding, forming or rolling flat sheet material
  into shape.

• A regular orthographic drawing of the object is
  made first.

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Surface Developments

• Then a development drawing is made to show the
  complete surface or surfaces laid out in a flat
  plane.

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A surface is developable . . .

• If a thin sheet of flexible material, such as
  paper, can be wrapped smoothly about its surface.

• If it is made up of flat surfaces or
  single-curved surfaces.
• Objects that have double-curved or warped
  surfaces can only be approximated by surface
  development.

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23-2 The Packaging Industry
StudiOhio
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Packaging

• The packaging industry involves surface
  development techniques.

StudiOhio
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Packaging

• Most products are packaged in containers made of
• Cardboard, Metal, or Plastic.
• Containers often must be attractive as well as
  functional.

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23-3 Radial Line Development of Flat Surfaces

• Right pyramid
• Oblique pyramid

Nick Rowe
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Developing a right pyramid

• With true length of edge lines shown
• 1. With 0 as center and with a radius equal to
  the true length of the lateral edges, draw an
  arc.
• 2. Drop a perpendicular from 0 to intersect the
  arc at point 3.

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Developing a right pyramid

• 3. With a radius equal to the length of the edges
  of the base, start at point 3 and step off the
  distances 3-2, 2-1, 3-4, and 4-1 on the large arc.

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Developing a right pyramid

• 4. Join these points with straight lines.
• 5. Connect these points to point 0 by straight
  lines to complete the development.

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23-4 Parallel Line Development of Cylindrical
Surfaces

• Hollow cylinder
• Truncated cylinder
• Elbow developments

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Development of a hollow cylinder

• The width of the development is equal to the
  height of the cylinder.
• The length of the development is equal to the
  circumference of the cylinder plus the seam
  allowance.

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Quick Quiz
?

• What is the test to determine if an object is
  developable?

• If a thin sheet of flexible material, such as
  paper, can be wrapped smoothly about its surface.

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23-5 Radial Line Development of Conical Surfaces

• Right cones
• Truncated cones
• Oblique cones

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Development of a right circular cone

• A right circular cone is symmetrical about the
  vertical axis
• Development is a sector of a circle

• Radius is the slant height

• Length around perimeter is the circumference of
  the base

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23-6 Development of Transition Pieces by
Triangulation

• Square to round transition pieces
• Offset transition pieces
• Transition pieces connecting two circular pipes

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Triangulation

• Nondevelopable surfaces can by developed
  approximately by triangulation.
• Surface is made from a series of triangular
  surfaces laid side by side.

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23-7 Development of a Sphere
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Methods for approximate development of a sphere

• Gore method

• Zone method

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23-8 Intersection of Flat Surfaces--Lines
Perpendicular

• Intersecting prisms

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Orthographic drawings of intersecting parts

• Lines of intersection must be plotted on the
  orthographic views.
• A numbering technique is valuable in plotting
  lines of intersection.

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23-9 Intersection of Cylindrical Surfaces

• 45? reducing tee
• 90? reducing tee

Nick Rowe
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90? Reducing Tee

• Element or reference lines are established about
  the cylinders.
• Element lines for the small cylinder are drawn to
  touch the large cylinder.

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90? Reducing Tee

• Each point of intersection is then projected down
  to the front view to intersect the corresponding
  element line, establishing the height at that
  point.

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90? Reducing Tee

• The points of intersection are connected by an
  irregular curve to produce the line of
  intersection.

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23-10 Intersecting Prisms

• Hexagon and cone
• Cone and cylinder
• Pyramid and cylinder

Daisuke Morita
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Intersecting cone and cylinder

• Intersections of the cone and cylinder elements
  in the top view are found and then projected down
  to the front view.

• A smooth curve is drawn through these points.

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23-11 Stampings

• Stamping terms
• Design considerations

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Definitions

• Stamping The process of pressworking sheet metal
  to change its shape by the use of punches and
  dies.
• Forming Stampings made by forming sheet metal to
  the shape desired without cutting or shearing the
  metal.
• Shearing Stampings made by shearing the sheet
  metal either to change the outline or to cut
  holes in the interior of the part.

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Definitions

• Blanking Shearing or cutting out the size and
  shape of a flat piece necessary to produce the
  desired finished part.
• Punching Forming a hole or opening in the part.

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Example of a typical stamping part
A preliminary sketch is made.
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Example of a typical stamping part

• Chamfers and circular holes are added for flange
  relief.

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Example of a typical stamping part

• The finished working drawing consists of a front,
  top, and two partial side views.

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Quick Quiz
?

• What is the process for approximately developing
  a nondevelopable surface?

• Triangulation