How do I Read Metal Fabrication Blueprints?

Written by edith hignutt
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How do I Read Metal Fabrication Blueprints?
Blueprints show how to fabricate steel items. (large steel girders image by Yali Shi from

Large buildings contain steel skeletons. Every "bone" or piece of steel carries a piecemark, or label, to differentiate it from the others. Each piece of steel started as a single blueprint, or detail drawing, before becoming part of the whole. A detailer laboured over that drawing, providing hole sizes, dimensions, and carefully labelling each and every part. Reading metal fabrication blueprints requires knowledge of standard detailing practices.

Skill level:

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  1. 1

    Place the blueprint on the table with the title block on the lower right side. The bill of materials, traditionally located above the title block on the right side of the paper, provides a list of the exact sizes and lengths of steel required to assemble the pieces drawn on this blueprint.

  2. 2

    Locate the piece mark. Each drawing will be labelled with a piece mark such as 1C1, 2B4, A6 or a similar designation with a letter and a number. The bill of material will provide a breakdown of material for each of the piece marks shown on this detail drawing.

  3. 3

    Look at one of the pieces drawn. Steel measurements are taken from left to right using running dimensions taken from the start of the steel or from a noted workpoint. For straight items or uncomplicated steel pieces, assume running dimensions begin at the start of the steel. If the detailer used a workpoint, a "wp" or a circle with an arrow will point to the workpoint from which dimensions are taken.

  4. 4

    Note the overall dimension traditionally located below the drawn piece. This information provides the total length of the piece from outside edge to outside edge when complete. The main member size will be listed here providing a double-check against the bill of material list.

  5. 5

    Look for arrows pointing to additional pieces. Parts such as angles or plates that attach to the main steel member will be labelled with part numbers using lower case letters and a number, such as pb2. The first letter indicates "a" for angle, "p" for plate, or other designations for less commonly used items.

    Locate the running dimension, which will labelled on a line drawn to the start of the attached piece.

  6. 6

    Find any holes to be drilled. The detailer provides running dimensions for holes by labelling them above the drawn piece and provides dimensions from the top of the main member to locate the holes on the piece.

  7. 7

    Read the boxes above the title block. This area contains miscellaneous drawing notes, such as whether the steel requires any paint and how many coats. This area also supplies the number and type of bolts the field will need to connect this piece to the building.

Tips and warnings

  • Metal fabrication shops fall into two main categories: a welded shop or a bolted shop. Welded shops attach primarily by welding as many pieces as possible. Bolted shops prefer to bolt items together.
  • Detailers generally start running dimensions at the end of the main steel member for bolted shops. Verify your shop's particular practices on running dimensions, as no industry standard exists.
  • While certain drawing elements remain common practice, the industry offers no specific detail drawing standards or requirements. Each detailer and each detailing company frequently has their own way of presenting information. Take a few minutes to peruse each drawing. Look for boxes with specific notes where special information such as certain paint types or connection requirements may be spelt out.

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