Line Conventions

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Line Conventions
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Line Conventions

• Line  conventions  convey  information  as
  succinctly as a physical example of the object
  itself.    
• The  appropriate  use  of standard line
  conventions enables fabricators to replicate
  objects based solely on your drawing

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Object Lines

• Any lines visible in a view that define edges or
  outlines of objects are drawn with lines referred
  to as object lines.
• Object lines are drawn as solid, thick lines.
• In drawings that do not have cutting planes,
  visible lines will be the thickest lines drawn.

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Hidden Lines

• Lines not readily apparent in a view of an object
  are hidden lines.
• Hidden lines are evenly-spaced, short dashes that
  begin and end as a dash in contact with the line
  from which it starts and stops.

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Center lines

• Center lines are used to indicate the center of a
  circle, arc, or any symmetrical object.
• Center lines are composed of long and short
  dashes, alternately and evenly spaced, with a
  long dash at each end.
• At intersecting points, center lines should be
  drawn as short dashes

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Viewing or Cutting Plane Lines

• To give a clearer view of obscure or oblique
  planes and interior or hidden features of an
  object that cannot be clearly observed in a
  conventional outside view, use viewing or cutting
  plane lines respectively.
• Viewing or cutting plane lines are the thickest
  of all lines.

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Viewing or Cutting Plane Lines

• Cutting plane lines, together with arrowheads and
  letters, make up the cutting plane indications.
• Arrowheads at the end of cutting plane lines
  indicate the direction from which you view the
  section.
• The cutting plane may be a simple, continuous
  plane, or it may be offset to show the interior
  detail to better advantage.

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Dimension lines

• Lines that define the parameters of a dimension
  are called dimension lines. Dimension lines are
  thin lines terminating in arrowheads.
• Place dimension lines no closer than 3/8" from
  the object outline. Parallel dimension lines
  should be a minimum of 1/4" apart.

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Dimension lines

• You may place parallel dimension lines more than
  1/4" apart so long as the spacing between
  dimension lines is uniform throughout the
  drawing.
• Dimension lines are generally broken in the
  center of the line to provide a space for the
  dimension figure.
• Dimension figures for parallel dimension lines
  are staggered.

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Extension lines

• Extension lines are thin lines that extend from
  the object outline or point on the object to a
  place outside the image area.
• Extension lines define areas for dimensions.
• You should leave a 1/16" gap between the object
  outline or point on the object and the beginning
  of the extension line.
• Extension lines project 1/8" beyond the outermost
  dimension line.
• Extension and dimension lines are drawn at right
  angles to each other.

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Leader lines

• Notes or dimensions that pertain to surfaces or
  parts are lead to that surface or part by leader
  lines.
• Leader lines are thin, solid lines that terminate
  in an arrowhead or dot.
• Use arrowheads when leader lines terminate at the
  outline of an object.
• Use dots when leader lines terminate within the
  outline of the object or on the surface of the
  object

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Arrowheads

• Arrowheads indicate the extent of the dimension.
• All arrowheads on a drawing should be uniform in
  size and style.
• Carelessly drawn arrowheads make drawings look
  unfinished and unprofessional.
• When indicating the radius of an arc or circle,
  place the arrowhead at the end of the dimension
  line that touches the object outline.
• The end of the dimension line terminates at the
  centerline of the arc or circle.

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Break Lines

• When an extended part of an object has a
  continuous shape and size, you can save space by
  abbreviating the object using zigzag or wavy
  lines.
• These zigzag or wavy lines are called break lines
  because you figuratively break away an
  unimportant segment of an object.
• LONG BREAK LINES Long break lines are ruled
  lines with freehand zigzags that reduce the size
  of the drawing required to delineate an object
  and reduce detail.

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Break Lines

• SHORT BREAK LINES To indicate a short break in
  an object, use thick, solid, wavy freehand lines.
  
• Rods, tubes, and bars have additional conventions
  that not only break their length but also imply
  the material or texture of the object.

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Phantom or datum lines

• To indicate alternate positions of parts,
  repeated detail, or to indicate a datum plane,
  use phantom or datum lines.
• Phantom or datum lines consist of a medium weight
  series of one long dash and two short dashes
  evenly spaced and terminating in a long dash.

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In Review

• Though these standards relate to technical
  drawing, which is far more precise than freehand
  sketching, their conventions should be used as a
  guide when sketching.

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References

• http//www.tpub.com/content/draftsman/