Computer Aided Design (CAD) with Onshape

BME254L - Spring 2026

Author
Affiliation

Dr. Mark Palmeri, M.D., Ph.D.

Duke University

Published

January 7, 2026

Computer Aided Design (CAD) with Onshape

Why CAD?

  • Formally capture 2D projection sketches → 3D parts.

  • Dimension consistency checks.

  • Assemble multiple parts to check fit, interfaces and simulate stress/strain/movement.

  • Translate to physical realization (e.g., 3D print, mil).

  • General technical drawings for manufacturing.

  • Capture design history, while facilitating iteration / change.

Onshape

  • We will be using Onshape, a cloud-based CAD package with a similar workflow to SolidWorks.

  • You will receive an email notification about being added to Duke’s Onshape instance: https://duke.onshape.com

Note

This is a specific Duke instance of Onshape, not the public one (https://onshape.com). Your Duke account creation will also automatically trigger an account being created in the non-Duke system too, but you cannot share projects between the two instances, so please make sure that you are using the Duke version for coursework!!

General Workflow

  • Sketch 2D profiles (dimensioned).

    • Use dimensions to size parts / features.

    • Use constraints to align sketch features to one another (avoid over constraining!).

    • Use contruction lines to help with sketching.

  • Extend 2D profiles to 3D parts.

    • Extrude (new, add, subtract, intersection)

    • Revolve

    • Utilize symmetry to mirror operations

  • Modify 3D parts

    • Fillet/chamfer edges

    • Hole tool

    • Combine common modifications into single step

    • Utilize “patterns” to repeat modifications

  • Assemble multiple parts.

  • Create mechanical drawings for machining / documentation.

Tips

  • Utilize part symmetry and patterns to reduce manual effort.

  • Define new sketch planes on part references that “make sense”.

  • Practice!!

    • There are many ways to create the same parts.

    • Some are more amenable to future modification than others; those aren’t always the fastest to create from scratch.

    • Experience is highly valuable on a resume.

Mechanical Design Considerations

Modifying Edges / Corners

  • Fillet - rounded edge/corner

  • Chamfer - sloped / angled corner / edge

Why modify edges?

  • Reduce stress concentrations (fillet > chamfer)

  • Reduce sharp edges

  • Ease assembly (potentially at a cost to manufacturing)

Type of Holes

  • CAD tools have Hole tools that can be very useful.

  • Hole diameter (and threading) can be specified by ANSI (e.g., #10-32, 32 tpi) or ISO (e.g., M5-0.8, mm pitch) standards

  • Mechanical drawings typically consistent of a table of holes (that can be automatically generated when using the Hole tool)

Mechanical Drawings

  • Multiview / orthographic projection

  • ISO 8015: Geometrical product specifications (GPS) — Fundamentals — Concepts, principles and rules

  • Dimension callouts / values should not overlap any part lines!

Design For Manufacturing (DFM) (and beyond)

  • Purpose

    • Protection (e.g., water, debris, sunlight)

    • Supporting relative position

    • Mounting

  • Loading

    • Shipping

    • Gravity / Momentum

    • Falls (especially corners!)

  • Buttons / Dials / Sliders

  • Interfaces

    • Cables

    • Displays

    • Buttons

  • Minimize everything else to save on time and cost!

Subtractive vs. Additive Manufacturing

  • Machining (subtractive)

    • Milling

    • Turning

    • Drilling

    • Grinding

  • Additive

    • 3D Printing

    • Laser Sintering

    • Stereolithography

In-Class Demo

  • Give operations meaningful names

  • Use variables for dimensions that may change