Sketch Edit Power

Overview

Students learn to modify OnShape sketches by changing dimensions and constraints (position/shape relationships), then connect those edits to drawing-geometry reasoning. This lesson builds from earlier sketch creation skills and prepares students for more complex CAD modeling.

Learning intentions

Students will be able to identify how changing a sketch measure affects the resulting triangle/shape geometry.
Students will be able to edit a sketch by updating dimensions and constraints in OnShape.
Students will be able to determine whether the given conditions produce a unique sketch configuration, multiple possibilities, or no valid configuration.
Students will be able to explain their editing choices using geometry language.

Success criteria

I can change a sketch dimension in OnShape and predict what will change in the sketch.
I can use constraints to reposition geometry correctly (without “breaking” the sketch).
I can classify a set of triangle/shape conditions as: unique, more than one, or no triangle.
I can justify my OnShape edits with references to angle/side measures or relationships.

Curriculum links

Geometry: Draw geometric shapes with given conditions, focusing on when conditions determine a unique triangle, more than one triangle, or no triangle.
Geometry: Solve problems involving scale drawings of geometric figures, including computing actual lengths and reproducing a scale drawing at a different scale.
Geometry: Use properties of angles in figures to write and solve simple equations for an unknown angle.

Lesson structure (45 minutes)

0–5 min · Hook + goal check. Teacher shows a screenshot of the same OnShape triangle sketch before/after edits and asks: “What do you think changed—size, position, or both?” Students share quick predictions, then the teacher states the lesson goal: edit sketches by modifying dimensions/positions and explain the effect.
5–12 min · Mini direct teach: “Edit = conditions.” Teacher demonstrates on a projector: select sketch → edit sketch → adjust a dimension → observe constraint/shape update; also shows an example where conflicting constraints produce a warning. Students follow on a device (or watch only if devices are limited) and record two “edit moves” they notice (dimension change vs. constraint change).
12–20 min · Guided practice: controlled edits (OnShape). Teacher gives a step-by-step task card for Sketch A: “Make this triangle match target measures.” Students open OnShape, find the provided starter part, and update: one side length and one angle (or one side and one angle relationship) to match given target values.

Teacher circulates with prompts:

“What constraint is being satisfied?”
“If you change this dimension slightly, does the sketch still look valid?”

20–28 min · Geometry reasoning check (unique / multiple / none). Teacher places three condition sets on the board (no calculator):

Set 1: three measures that should determine a unique triangle (e.g., SSS).
Set 2: two angles and a side that can lead to more than one configuration if scale/placement is not fixed in the sketch.
Set 3: incompatible angle/side measures that should produce no triangle. Students use a quick “thumbs” response (unique / multiple / none), then discuss with a partner how that relates to OnShape (constraints either lock the shape or conflict).

28–37 min · Independent task: “Fix the sketch” challenge. Teacher provides a second sketch (Sketch B) with a goal: “Your sketch is wrong—fix it by editing dimensions/constraints until it matches the target diagram.” Students identify what is off (e.g., a dimension not matching, wrong position of points, or angle not achieved), then perform the minimum number of edits to reach success. They must update at least two constraints/dimensions and keep the sketch fully defined as required.

Teacher checks for the reasoning requirement: students write a 1–2 sentence explanation in their notebook: “I changed ____ because the conditions indicate ____ (unique/multiple/none) and OnShape showed that ____.”

37–45 min · Share-out + exit ticket. Students submit an exit ticket on paper or LMS:

“In one sentence, explain the difference between changing a dimension and changing a constraint.”
“Given your Sketch B conditions, circle: unique / multiple / none, and explain why in 1–2 sentences.”

Resources

OnShape accounts and teacher-provided starter files (Sketch A and Sketch B)
Projector or teacher screen for demonstration
Student devices (laptop/tablet) and headphones if needed
Task cards for Sketch A and Sketch B
Geometry reasoning condition cards (unique/multiple/none)
Notebook or worksheet for explanations
Exit tickets (paper or digital)
Optional: protractor/straightedge handout for quick reference

Assessment

Formative checks during circulation: verify students can edit a dimension/constraint and predict sketch changes.
Quick partner discussion at the unique/multiple/none step to catch misconceptions.
Exit ticket responses: measure understanding of (1) edit types and (2) reasoning about conditions determining triangle configuration.

Differentiation

Support: Provide a “Constraint vs. Dimension” sentence starter bank (e.g., “Changing a dimension changes…, while a constraint forces…”). Offer a checklist for OnShape steps (select sketch → edit sketch → update dimension → verify constraints).
Support: For students who finish early, allow them to replay the guided demo recording and compare with their own steps.
Extension: Students who complete Sketch B early can attempt an additional variation: change one target measure slightly and predict whether the sketch should remain valid or become over/under-constrained.
EAL/SEN: Use visual arrows on task cards (what to click) and include a minimal word bank (dimension, constraint, angle, length, position, conflict).

Exit ticket prompt (for quick printing)

Sentence 1: “Changing a dimension is different from changing a constraint because ________.”
Sentence 2: “My Sketch B conditions are most consistent with a ____ triangle because ________.” (unique / more than one / no triangle)

Teaching Instructions