The True Length

  • When a drawing is made without any dimensioning, it can be hard to tell actual length of a side due to projection.
  • The true length of a line is its actual length and can be found in an orthgraphic drawing's top and front views.
    • Principle lines are lines on the drawing that already give the true length
      • These lines can be identified by looking for a line that is:
        • a dot/invisible in one view
        • parallel to an axes in one view
      • The true lengths of the lines are in the other view.
    • For a diagonal line, there are many ways to find its true length, but for now we look at the radial method.
      1. Take a compass, and make the diagonal in one view the "radius"
      2. Draw horizontal line from one of the end points (Referred to as A) of the diagonal.
      3. From A, use the compass to draw an arc from the other point(B) to the horizontal line.
      4. At the point of intersection, draw a vertical line down to the other view.
      5. Draw a horizontal line from B on the OTHER VIEW to that vertical line.
      6. Join the point of intersection with point A in this other view.
      7. This line is the true length of line AB.