25 Blueprints

There are three main types of blueprint drawings: mechanical/engineering, architectural, and shop/fabrication. Welders will most often have to read and interpret shop or fabrication drawings. Drawings can be done in isometric view (a three-dimensional view showing three sides in a single drawing) or orthographic view (a two-dimensional view, requiring multiple views to show the whole of a part).

When using blueprints in the welding shop, remember that drawings are expensive to both produce and to copy. Do not write unauthorized notes on a drawing, always protect drawings from dirt and liquids, never fold a drawing, and be sure to store them in a safe, easily accessible area.

Types of Blueprints

Mechanical or engineering drawings have been used for centuries (see: Leonardo da Vinci’s notebooks). They are often a set or group of drawings and may contain various pages. Mechanical drawings are often used for bidding contracts or for developing fabrication drawings (the design of the building’s skeleton, mechanical systems, electrical, ventilation, or plumbing systems).

Architectural drawings show the initial design of a structure. They allow architects to match what the customer wants, ensure the building looks good in its immediate surroundings, and check that the building meets building codes. Architectural drawings often show building elevation and floor plans.

Fabrication or shop drawings provide information to the fabricator (the person doing the construction). They include details on building individual parts, such as dimensions, connections, welds, holes or cuts, and finishing requirements. These drawings allow the fabricator to select the proper steel shapes and sizes from stock.

Dimensions

The most important information on any drawing is probably the dimensions. These are numerical values that describe the size, location, geometric characteristics, or surface textures of various features. Dimensional tolerances show how much or how little you can deviate from the written value, and are usually expressed as +/- the maximum amount of deviation allowed. When creating a blueprint, always remember to:

• Place dimensions so it is easy to determine what is being measured,
• Avoid using different units of measure on the same blueprint (metric vs English, fractions vs decimals, etc.),
• Avoid running dimension or extension lines (see below) across or through each other, and
• Keep the drawing clean and easy to read.

Types of Lines

Blueprints use different lines for different purposes. To review a few of the line types:

• Cutting plane lines: used to show imaginary cuts (that only exist in the blueprint, not in the actual part) to reveal more details
  • These lines are thick, with their ends at 90° and arrowheads showing direction from which the view is taken.
• Object or visible lines: used to outline visible edges and contours
  • These lines are thick and continuous.
• Hidden lines: used for hidden edges and internal features, such as the internal workings of a hollow object
  • These lines are medium weight, typically 1/4″ dashes separated by 1/16″ spaces.
• Center lines: used to show the center of symmetrical objects or features such as holes
  • These lines are fine and dark with alternating short and long dashes.
• Section lines: used to show interior features, cut surfaces, or the type of material being cut
  • These lines are typically fine and dark, but otherwise can vary depending on the company that drew the blueprint.
• Break lines: used to remove sections for clarity, to provide a clearer view of parts below the removed part, or to shorten long parts
  • Short break lines show a partial section, while long break lines show a shortened section of a longer part (to conserve paper space).
• Leaders and arrows: used to point out more details, an important idea, or otherwise add a note
  • These lines are fine with an arrowhead on only one end.
• Phantom lines: used to show adjacent positions of related parts, alternate positions of moving parts, repeated details, or filleted and rounded corners
  • These lines are thin and dark with long dashes alternating with pairs of short dashes.
• Dimension lines: used to indicate extent and direction of a dimension
  • These lines are capped on each end with arrowheads and placed between extension lines. The dimension is usually placed at the midpoint of the line and can show the tolerance with +/-.
• Extension lines: used to indicate the termination of a dimension
  • These lines have the same line weight as the dimension line.