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CAD Fundamentals & Orthographic Projection Cheat Sheet
A printable reference covering CAD basics, dimensioning, scale, line types, and orthographic projection for grades 8-12.
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Engineering drawings communicate how an object should be made, measured, and checked. This cheat sheet covers the CAD fundamentals students need to create clear technical drawings and interpret orthographic views. It helps students organize models, use correct drawing conventions, and avoid common projection mistakes. These skills are important for design, manufacturing, robotics, architecture, and engineering projects. The core ideas include using accurate units, drawing with standard line types, applying dimensions clearly, and choosing the correct scale. Orthographic projection shows a 3D object using flat 2D views such as the front, top, and right side. Views must align so that width, height, and depth are transferred consistently. Good CAD work depends on precision, constraints, layers, clean geometry, and readable annotations.
Key Facts
- In CAD, 1:1 scale means the digital model is drawn at its real size, and the drawing sheet scale controls how it prints.
- Orthographic projection represents a 3D object with separate 2D views, usually front, top, and right side.
- The front view should show the most detail and the most recognizable shape of the object.
- In third-angle projection, the top view is placed above the front view and the right-side view is placed to the right of the front view.
- Visible edges are drawn with thick continuous lines, while hidden edges are drawn with dashed lines.
- Centerlines use long-short-long dash patterns and mark axes of symmetry, holes, circles, and cylindrical features.
- A dimension should include the measured value, extension lines, dimension lines, and arrows or ticks, with units understood from the drawing standard.
- Scale factor = drawing length / actual length, so a 2:1 scale makes the drawing twice the actual size and a 1:2 scale makes it half size.
Vocabulary
- CAD
- CAD means computer-aided design, which uses software to create, edit, analyze, and document technical drawings or 3D models.
- Orthographic Projection
- Orthographic projection is a drawing method that shows a 3D object as multiple flat 2D views without perspective distortion.
- Dimension
- A dimension is a labeled measurement that describes the size or location of a feature on an engineering drawing.
- Scale
- Scale is the ratio between a drawing size and the actual object size, such as 1:1, 2:1, or 1:2.
- Constraint
- A constraint is a CAD rule that controls geometry, such as keeping lines horizontal, equal in length, parallel, or a fixed distance apart.
- Hidden Line
- A hidden line is a dashed line used to show an edge or feature that cannot be seen directly in that view.
Common Mistakes to Avoid
- Mixing up top and side views is wrong because orthographic views must stay aligned with the front view and preserve width, height, and depth correctly.
- Drawing the model at paper scale instead of real size is wrong because CAD models should usually be created full size, then scaled only on the drawing sheet.
- Over-dimensioning a part is wrong because repeated or unnecessary measurements can create confusion and make the drawing harder to inspect.
- Using the same line style for visible, hidden, and center features is wrong because line types communicate different kinds of geometry.
- Choosing a poor front view is wrong because it can hide important features and make the drawing require more views than necessary.
Practice Questions
- 1 A part is 80 mm long in real life. If it is printed at a 1:2 scale, how long should it appear on the drawing?
- 2 A CAD drawing shows a bracket at 2:1 scale. If a hole appears 24 mm in diameter on the print, what is the actual hole diameter?
- 3 An object has a front view width of 60 mm and height of 40 mm. Its top view shows a depth of 30 mm. What dimensions should the right-side view show?
- 4 Explain why an engineer might use hidden lines in one orthographic view but not in another view of the same object.