Orthographic Projection and the Glass Box

Each view looks straight at the part from one direction

A pictorial helps you recognize a part. A multiview drawing helps you describe its shape without the apparent shrinkage of perspective. In orthographic projection, the lines of sight are parallel and perpendicular to the viewing plane.

Choose a front direction and keep the part fixed. Look straight from the front, from above, and from the right. Do not turn the part independently to make each view look convenient.

Front and rear: Show width and height; depth points toward or away from you.
Top and bottom: Show width and depth; height points toward or away from you.
Right and left: Show depth and height; width points toward or away from you.

A face parallel to its viewing plane shows its true shape at the drawing's scale. A face tilted to that plane is foreshortened; a face viewed exactly edge-on becomes a line.

The glass box unfolds into six related views

Imagine the part inside a transparent box. For third-angle projection, trace what you see onto the box face between you and the part. Each face receives one principal view: front, rear, top, bottom, left, and right.

A fixed block inside a transparent box with front, top, and right viewing planes; beside it a third-angle net places top above front, bottom below, left to the left, right to the right, and rear beyond right. — Keep the front face fixed. Hinge the top upward, bottom downward, and side faces outward. The rear can unfold beyond a side face; this net places it beyond the right.

The names identify the direction you look from. A right-side view means you stood at the part's right, even if a different projection convention puts that view elsewhere on the sheet. Compare First-Angle and Third-Angle Projection.

Predict a view, then compare it with the same block part; Interactive

Predict a view, then compare it with the same block part

Choose a part and a viewing direction in the explorer. Before revealing the view, predict its outline and any step edges. Switch the layout convention and notice what moves on the sheet. The part and the named views stay the same.

A block with a tall left strip and a lower right shelf, extruded uniformly in depth. Front is an L-shaped outline, top is a rectangle split at the step, and right is a rectangle with a visible horizontal shelf edge. — Static example: the tall strip is on the left of the front view and extends through the full depth. The top view gives its width; the right view gives its height.

These are simple solids with constant depth. Construction guides are teaching aids. The explorer includes the step edges visible or hidden from each selected direction; it is not a dimensioned manufacturing drawing.

Use alignment to follow one feature through the drawing; Checklist

Use alignment to follow one feature through the drawing

Identify the front view and confirm the projection convention.
Track the same left-to-right position between front and top: they share width.
Track the same elevation between front and side: they share height.
Compare front-to-back positions between top and side: they share depth.
Explain each solid or dashed edge using the shape seen in another view.

At the same scale, a feature cannot be one width in the front view and a different width in the top view. A 45° miter construction can transfer depth between top and side while sketching; that construction line is not an edge of the part.

Why one view can hide an entire change in shape

Looking from the front collapses depth. A shallow block and a deep block can have identical front outlines. Looking down on them separates those possibilities. Even three matching outside outlines do not prove that internal holes or recesses are identical; hidden lines, sections, dimensions, and notes still matter.

NPTEL's projection-method lesson and Autodesk's projection-angle explanation provide another way to compare the conventions.

Next, decide which views the part actually needs.

Match the pictorial to its front, top, and right views; Practice

Match the pictorial to its front, top, and right views

Identify each numbered candidate using the viewing directions on the pictorial. These candidates are arranged as answer choices, not in a first-angle or third-angle layout.

A tall-left stepped block with front, top, and right viewing directions. Candidate 1 is a rectangle with a horizontal line; candidate 2 has a tall left step in its outline; candidate 3 is a rectangle with a vertical line near its left edge.

Use the self-checks to test your choices and read the explanations.

Identify the front Identify the top Identify the right