Blueprint Line Types Explained | Visible, Hidden, Center, Section and Dimension Lines

Main ideas and lessons

• Engineering drawings/blueprints are a “graphical language” that transfer design intent from the engineer to the people who will manufacture the part.
• Line types and their consistency/quality are critical so the blueprint accurately represents the final product.
• The specific line styles described are standards/conventions, but individual drawing specifications may vary.

Line types (concepts + how they’re used)

Visible / Object lines

• Appearance: Solid lines with a thick weight
• Purpose: Show the edges/lines on the actual object (visible features)

Hidden lines

• Appearance: Short dashes, evenly spaced
• Purpose: Show features not visible because they’re inside/behind the object
• Rule of dash start: Begins with a dash that is in contact with the line it originates from, unless that would create a continuation of a full line

Center lines

• Appearance: Alternating long and short dashes, evenly spaced; long dash at each end
• Special case: Very short center lines may be unbroken if it avoids confusion
• Usage notes:
  • In a front view, center lines cross without voids
  • In a side view, a center line can indicate the center of a hole

Section lines

• Appearance: Generally thin full lines, with variation depending on material
• Purpose: Show exposed surfaces in a sectional (cut) view
• Interpretation: Indicate where material would be if the part were cut “as if with a saw”
• Multiple sections: Different patterns/directions denote different sections

Dimension lines

• Appearance: Typically arrowheads at each end
• Purpose: Indicate the measured dimension value of a part
• Rule: Usually unbroken, except where space is needed to place the dimension text/number

Extension lines

• Appearance/position: Small visible gap from the part outline, usually perpendicular to the associated dimension line
• Purpose: Show the limits/extent over which the dimension applies

Leader lines

• Appearance: Unbroken lines ending in an arrowhead
• Purpose: Connect a number, note, or reference to the part/portion it applies to
• Common reason for use: When the dimension can’t fit within the dimension line

Cutting plane lines

• Purpose: Indicate the plane(s) along which a section is taken
• Direction meaning: Arrows show the view direction (where the viewer’s eyes go after the cut)

Viewing plane lines

• Difference from cutting plane lines: They do not actually cut the part; no full section is generated
• Purpose: Allow an interior/detail view to be shown when a full section isn’t necessary

Break lines

Used to show portions of the part where detail isn’t useful, typically to save space or to reveal further details.

• Two types:
  • Long break lines
    • Appearance: Full ruled lines with freehand zigzags
    • Purpose: Breaks in shafts, rods, tubes, rope, etc., removing a portion for convenience
  • Short breaks
    • Appearance: Solid freehand lines
    • Purpose: Smaller section views where removing material clarifies features

Phantom lines

• Appearance: Alternating one long and two short dashes, evenly spaced; long dash at each end
• Three main uses:
  1. Indicate the alternate position of moving parts
  2. Show the position of related parts to clarify interfaces (especially with existing or missing parts)
  3. Show repeated detail
     • Example: A spring where not every coil must be drawn; phantom lines indicate the pattern continues

Speakers / sources featured

• No individual speakers or external sources are mentioned in the provided subtitles.