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CAD & Design·Lesson 2 of 31

Orthographic Projection and Engineering Drawings

Discover how engineers flatten a 3D part into a few exact 2D views that anyone in the world can build from.

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What orthographic projection is for

One photo of a part hides faces and distorts sizes — you can't build from it. The fix is orthographic projection: you look straight at the part along an axis and project its outline flat. Because you're looking dead-on with no perspective, each view is true-to-scale and you can measure straight off it.

The standard views

You could draw six faces, but most parts need only three:

  • Front — the most descriptive face, picked first
  • Top — looking straight down
  • Right side — looking from the right

These usually capture everything. Features hidden behind a face are drawn as dashed hidden lines, and a centerline (long-short dashes) marks the axis of every hole and round feature — which is most of what you'll dimension on an FRC part.

View layout: get it right or get the wrong part

There are two conventions for arranging views on a sheet. FRC and U.S. manufacturing use third-angle projection: the top view sits above the front view and the right-side view sits to the right — exactly where your intuition expects. (The other convention, first-angle, flips them; you'll only meet it on drawings from overseas suppliers, flagged by a small symbol in the title block.) Default to third-angle and you'll match every sponsor shop and CNC service you're likely to use.

Reading a drawing

A complete drawing usually has:

  1. The views with hidden lines and centerlines
  2. Dimensions (next lesson)
  3. A title block — part name, scale, units, material
  4. Sometimes a section view (the part "sliced" to show interior features) or an isometric for clarity

Why this still matters when you model in 3D

You'll model in 3D CAD like Onshape, but drawings run the build season:

  • When you hand a part to a sponsor's machine shop or a waterjet/CNC service, they often cut from a 2D drawing. If your views are unclear, you get the wrong part — and during build season you don't get that week back.
  • Reading a COTS (commercial off-the-shelf) part's drawing — a gearbox, a bearing, a wheel — lets you confirm its bolt-hole pattern and mounting clearances before you design around it.
  • Exporting a clean drawing from your model is the step that turns a nice CAD picture into something someone can actually make.

Practice this now

Take an L-bracket with one hole. On paper, draw its front, top, and right views in third-angle layout. Add a centerline through the hole and a hidden line where the hole passes behind a face. Compare with a teammate — if your views disagree, your mental model of the part needs another pass before you trust it in CAD.

Key takeaways

  • Orthographic projection uses parallel, perpendicular projectors so each 2D view is true-to-scale and measurable.
  • Most drawings use three views — front, top, and right side — with dashed hidden lines and centerlines.
  • Third-angle projection is the U.S./ASME Y14.3 standard; first-angle is the international/ISO standard, and they arrange views oppositely.
  • A truncated-cone symbol in the title block tells you which projection convention a drawing uses.
  • FRC parts sent to machine shops or CNC/waterjet services are built from these drawings, so clarity prevents wrong parts.

Go deeper

Lesson quiz

Required

Answer all 3 questions correctly to complete this lesson.

1.Which projection convention is the standard for engineering drawings in the United States?

2.What makes orthographic views measurable and true-to-scale?

3.On a drawing, what does a dashed (hidden) line represent?

Answer every question to submit.