Drawing Fundamentals: Orthographic Projection and Views

Why Welders Need to Read Drawings

Every structural steel component you weld starts as a drawing. Before a single arc is struck, fabricators, fitters, and welders must agree on exactly what shape a part has, how big it is, and where every hole, notch, and weld joint falls. Blueprint reading is therefore a core trade skill tested by AWS SENSE, NCCER, and every structural employer you will encounter. This lesson focuses on the foundational system behind all engineering drawings: orthographic projection.

What Is Orthographic Projection?

Orthographic projection is a method of representing a three-dimensional object on a flat, two-dimensional surface by projecting parallel lines from each surface of the object onto a flat plane. Think of shining a light perfectly perpendicular to one face of a part and tracing the shadow — that shadow is an orthographic view. Because the projection lines are parallel (not angled as in perspective drawing), every feature is shown at its true size and shape on the plane that is parallel to it. This accuracy is why engineering drawings use orthographic projection instead of artistic perspective.

The Six Standard Views

An imaginary transparent box is placed around the object. Each of the six interior faces of the box receives one projected view:

| View Name | What You See |

|---|---|

| Front | The most descriptive face; chosen by the drafter |

| Top (Plan) | Looking straight down |

| Bottom | Looking straight up |

| Right Side | Looking from the right |

| Left Side | Looking from the left |

| Rear | Looking from behind |

When the box is unfolded flat, the six views arrange themselves in a fixed pattern around the front view. In practice, most structural steel drawings show only the front, top, and right-side views — the three that together fully describe the part. A drafter adds other views only when needed to show a feature hidden by those three.

First-Angle vs. Third-Angle Projection

Two international conventions exist for unfolding the projection box:

• Third-angle projection is the US standard (ASME Y14.3). The view is placed on the same side as the direction you look. The top view appears above the front view; the right-side view appears to the right of the front view. You will see the third-angle symbol — two circles forming a truncated cone — in the title block of US structural drawings.
• First-angle projection is used in much of Europe and internationally. The view is placed on the opposite side from the direction you look. The top view appears below the front view. Its symbol shows the same cone from the opposite end.

As a welder in US structural work, you will almost always work with third-angle drawings. Always check the title block for the projection symbol before interpreting any view arrangement.

Reading a Three-View Drawing

Follow this systematic process:

1. Orient yourself. Locate the front view — it is typically the largest and most complex view.

2. Align views. In third-angle projection, the top view sits directly above the front view and shares the same width. The right-side view sits directly to the right of the front view and shares the same height.

3. Project between views. Any vertical line in the front view projects straight up into the top view. Any horizontal line in the front view projects straight across into the right-side view. Features must line up across views — use a straightedge.

4. Interpret line types. Solid visible lines show edges you can see. Dashed hidden lines show edges behind a surface. Center lines (alternating long and short dashes) locate holes, round features, and symmetry axes.

5. Build the mental 3-D model. Combine information from all three views to determine the true shape. No single view tells the whole story.

Auxiliary Views

When a structural part has a surface that is angled relative to the standard planes — such as a gusset plate welded at 45° — none of the six standard views will show that surface in its true size and shape. A drafter adds an auxiliary view projected perpendicular to that inclined surface. Auxiliary views are labeled with a viewing direction arrow and a letter (e.g., "VIEW A-A").

Welding Symbols and Views

Welding symbols are placed on the drawing view that shows the joint most clearly. An arrow points to the joint; a reference line carries the symbol elements. You will study welding symbols in depth in the next lesson, but recognizing which view the symbol appears on — and therefore which surface carries the weld — depends entirely on your ability to read orthographic views correctly.

Safety in the Drawing Area

Blueprint reading is a classroom and shop-office activity, but a few safety habits apply:

• Never mark on or fold original fabrication drawings. Work from prints or digital copies. Altered drawings can cause mis-cuts, wrong weld sizes, and structural failures.
• Confirm revision status. Always verify you are reading the current revision number (found in the title block). Fabricating from a superseded drawing is a common and serious error on structural job sites.
• Carry rolled drawings carefully in the shop — sharp tube cores and large format paper create trip and laceration hazards near moving equipment.

Key Takeaway

Orthographic projection gives every trade on a construction project — welders, fitters, ironworkers, inspectors — a single shared language for shape. Master the three-view layout and the rules of third-angle projection, and every structural fabrication drawing you encounter will begin to make sense immediately.