Technical graphics _technical drawing__1_ by hcj

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									               Class 10_1
• Section views
• Practice drawing, sketching
• Introduction to dimensioning
Questions about DP?
                  Review
• Introduction to the nature and purpose of
  technical drawings
        Typical “projections”
• Orthographic projection (the fundamental
  engineering drawing)
• Isometric projection (a pictorial view)
• Oblique projection (another pictorial view)
      Stages in making a sketch
•   Block-out the outline with “construction lines”
•   Block-out the major features
•   Refine shapes
•   Darken part lines

• Tips: Use construction lines liberally, draw big
  (use entire page), pay attention to proportions,
  relax and practice.
                    Lines
Line types (e.g., part, hidden, center)
Line values (e.g., thick, intermediate,
 construction)

It is important to use the proper line type and
   line value in your drawings. It
   communicates important information and
   makes drawings easier to understand.
Example of lines
             Section views
• Section views “cut-away” part of the object
  so that internal details can be revealed.
             Section views
• Section view are also used to show
  assembly details
     Section view conventions
• Cut surface is filled with a “hatch”
• Part lines behind cutting plane are shown
• Hidden lines behind cutting plane are
  generally not shown
• Section view can take the place of one
  orthogonal view or can be auxiliary views
         Section view types
• Many section view types. A few
  examples…
        Review: section view
            conventions
• Cut surface is filled with a “hatch”
• Part lines behind cutting plane are shown
• Hidden lines behind cutting plane are
  generally not shown
• Section view can take the place of one
  orthogonal view or can be auxiliary views
          Drawing practice
• Freehand sketches
• Draw two views of the object, one of which
  is a full section view
• Remember: block out the entire drawing
  using construction lines, pay attention to
  proportions, use proper section view
  conventions
             Dimensioning
• Dimensioning of technical drawing is, of
  course, crucial
• There are well established conventions
  (rules) for proper dimensioning
• Brief description given on overhead
  projector, and handout
Reading of the rules…
Each feature of an object is dimensioned once, and
only once.
Dimension should be selected to suit the function of the
object.
Dimensions should be attached to the most descriptive view
of the feature being dimensioned.
Dimensions should not specify the manufacturing
method.
Avoid dimensioning to hidden lines.
Avoid placing dimension inside the object.
Dimensions should be aligned and grouped to promote
uniform appearance.
Dimension lines should be unbroken except for the number
between arrowheads.
There should be a visible gap between the object and the
extension line.
Extension lines should extend past the last dimension line.
Leader lines used to dimension circles or arcs should be radial.
Dimensions should be oriented to be read from the
bottom of the drawing.
Positive cylinders should be dimensioned in the
longitudinal view.
Diameters are dimensioned with the numerical value
preceded by the diameter symbol (f).

Radii are dimensioned with the numerical value
preceded by the radius symbol (R).

Dimension to the center of cylinders, holes, and arcs.
         Dimensioning practice

•   Draw a 3-view orthographic projection
•   Dimension fully
•   You can guess the dimensions
•   Take the hole diameter as 1 inch
•   Remember to leave room for dimensions

								
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