3D Feature Foundations

Overview

In this lesson (7 of 15) from “Mastering OnShape CAD Basics,” students learn how sketches become 3D objects using basic features. The focus connects geometry measurements and conditions to real modeling steps in OnShape.

Learning intentions

• Students will be able to explain how 2D sketches define 3D shapes using feature operations.
• Students will be able to construct (or choose) consistent sketches that support correct 3D results.
• Students will be able to identify when a set of sketch measurements would determine a unique shape or multiple possibilities.
• Students will be able to use geometric reasoning to predict what changes in a sketch will do to a 3D model.

Success criteria

• I can describe the relationship between sketch geometry and a 3D feature (extrude, cut, or revolve conceptually).
• I can interpret given angle/side conditions and predict whether a triangle sketch would be uniquely determined, multiple, or impossible.
• I can update a sketch constraint/measurement and correctly predict how the 3D model will change.
• I can check my model by verifying dimensions/angles against the plan.

Curriculum links

• Geometry — drawing and constructing triangles from angle/side measures and analyzing uniqueness or nonexistence.
• Geometry — describing 2D cross-sections from 3D slices using right rectangular prism/pyramid examples.
• Geometry — solving area/volume problems involving composite shapes including right prisms built from polygons/triangles.
• Geometry — using scale drawings and reproducing figures at different scales.

Lesson structure (45 minutes)

1. 0–5 min · Hook (real-world prompt). Teacher displays a finished OnShape part and a screenshot of its sketch, then asks: “What information in the sketch controls the final 3D size?” Students do a quick think-write: list 2 sketch details they think matter (e.g., dimensions, angles, constraints).

2. 5–12 min · Mini direct instruction (3D features from sketches). Teacher explains: a sketch is a 2D “plan,” and 3D features pull/cut/revolve that plan into shape; students learn the vocabulary “extrude,” “cut,” and “profile.” Students follow along by labeling on a printed diagram: profile region, direction/axis, and the idea of “depth” or “height” for features.

3. 12–20 min · Geometry reasoning check (uniqueness). Teacher gives two short scenarios on the board:

• Scenario A: “A triangle is given two angles and a side length between them.”
• Scenario B: “A triangle is given three sides that are all different.” Students answer: Which scenario leads to a unique triangle, and which could allow multiple arrangements? Teacher connects to “conditions determine unique triangle vs more than one vs no triangle,” emphasizing measurement consistency. Then teacher bridges to CAD: “If your sketch is under-constrained or inconsistent, OnShape may let choices move—or refuse to build.”

4. 20–33 min · Guided build in OnShape (sketch → feature). Teacher assigns a starter file (or teacher-created template) and guides steps:

• Open Part Studio
• Create a sketch on the correct plane
• Draw a simple profile (rectangle or right-triangle-based profile)
• Apply constraints/dimensions (students match a “spec card”)
• Create a feature (extrude or cut) using the sketch profile Students work in pairs: one drives mouse/typing, the other checks dimensions against the spec card; they must complete one working 3D feature.

5. 33–40 min · Cross-section prediction (2D from 3D). Teacher presents a right rectangular prism picture and asks: “If we slice it at a certain height, what 2D shape appears?” Students sketch the expected cross-section shape on their paper and connect it to the idea of “plane sections” from 3D objects.

6. 40–45 min · Exit ticket (quick assessment). Students submit a short response:

• “Describe one sketch measurement that controls the 3D feature.”
• “If I change that measurement, what happens to the volume/size, and how do you know?”
• One sentence answering the uniqueness question: “Do the given conditions determine a unique triangle, more than one, or no triangle?”

Resources

• OnShape accounts/logins and Part Studio template files for the lesson
• Projector/teacher display showing sketch and 3D feature
• “Spec cards” with dimensions/constraints for each pair (consistent, age-appropriate profiles)
• Printed diagram of profile vs feature direction
• Geometry scenario cards (uniqueness triangle conditions)
• Student paper and pencils for cross-section sketches
• Exit ticket slips or a digital form (teacher choice)

Assessment

• Teacher circulates during the guided build: checks whether sketches are constrained/dimensioned to spec before creating the feature
• Quick oral checks in the geometry uniqueness discussion (students justify unique vs multiple/no triangle)
• Exit ticket checks for correct explanation of sketch-to-3D control and a reasonable prediction about size/volume change

Differentiation

• Support: Provide a “constraint checklist” (e.g., right angles, locked lengths, angle given) and sentence starters for exit tickets.
• Support: Pair students strategically so one is comfortable with geometry vocabulary and one with OnShape navigation.
• Extension: Students who finish early can attempt a second feature (a small cut) that uses the same sketch profile and record one prediction they made before changing anything.
• EAL/SEN: Offer a word bank for feature language (sketch, profile, extrude, cut, dimension, angle, constraint) and allow drawing answers (cross-sections) instead of only writing.