Orthographic Projection and Engineering Drawings

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.

This lesson was adapted from learnfrc.com.