How Onshape Fixes the Broken Promise of Model-Based Definition

For all the incredible advancements in 3D CAD over the last few decades, a fundamental disconnect still plagues the manufacturing process. Engineers design in rich, three-dimensional spaces, yet the crucial instructions on how to actually build and inspect those parts are often siloed, disconnected, or lost in translation.

The industry’s proposed solution to this problem—Model-Based Definition (MBD)—isn't a new concept. In fact, it has been around for decades. Yet, despite its obvious logical appeal, MBD has struggled to achieve widespread adoption in mainstream CAD workflows.

Let's explore what MBD is supposed to be, why the traditional approach failed to launch, and how a modern approach is finally making it practical.

What Exactly is MBD?

At its core, Model-Based Definition is the practice of capturing the design intent and the limits of requirements directly within the 3D model, structuring it so that it can be easily utilized by both humans and machines downstream.

To break that down:

• Design Intent: The physical reality of the part—its sizes, positions, and shape characteristics.
• Limits of Requirements: The allowable tolerance ranges permissible for each of those physical requirements.
• Downstream Utilization: The ultimate destination for this data. MBD data feeds into 2D drawings, design reviews, CAM and manufacturing software, and QA/inspection processes.

Instead of treating the 3D model as a mere geometrical placeholder while the "real" manufacturing data lives entirely on a disconnected 2D drawing, MBD makes the 3D model the single source of truth.

The High Cost of Bad (or Missing) Data

When MBD data is missing, incorrect, or poorly communicated, the ripple effects are felt throughout the entire production cycle. A beautifully modeled part is useless if the manufacturing floor doesn't know the precise constraints required to make it function.

The implications of flawed MBD data are severe:

• Poor or Impossible Fitment: Parts that look perfect on a screen may clash or fail to assemble on the factory floor if tolerances aren't accurately captured and communicated.
• Misinterpreted Intent: Ambiguity leads to assumptions. When machinists have to guess what the engineer intended, errors are inevitable.
• Failing Inspections: QA teams cannot properly validate a part without clear, accessible requirement limits, leading to unjustified part rejections or—worse—passing defective parts.
• Cost Inefficiencies and Overruns: Every misinterpretation, scrapped part, and failed assembly compounds into massive financial losses and delayed time-to-market.

Failed Implementations: Why Isn't MBD Everywhere?

STEP AP242 Export for Automated Inspection

If bad data causes so much pain, and MBD solves it, why isn't every engineering team using MBD today?

The truth is, legacy CAD providers have fundamentally misunderstood what it takes to make MBD functional for the modern enterprise. By relying on disconnected desktop files, rigid interfaces, and manual processes, MBD has historically been treated as a cumbersome chore rather than an accessible, automated, and seamlessly integrated tool.

Here is why it hasn't caught on:

• Accessibility: Traditional CAD locks MBD data behind expensive software licenses and heavy desktop installations. To succeed, modern manufacturing requires anytime, anywhere access to a guaranteed single source of truth. If a machinist or QA inspector on the shop floor cannot easily open and interact with the latest annotated 3D model on a tablet or web browser, the system fails. This lack of true accessibility not only causes daily friction but also threatens overall business continuity when teams are distributed or unexpected disruptions occur.
• Ease of use: In legacy systems, applying Product and Manufacturing Information (PMI) is a notoriously tedious, manual process. Instead of having essential ASME and ISO standards embedded natively into the software, engineers are forced to constantly input and configure baseline geometric dimensioning and tolerancing (GD&T) rules that should simply be available by default.
• Customization: Manufacturing isn't one-size-fits-all. Legacy MBD tools often force engineers into rigid, hard-coded annotation styles that don't align with their company's specific drawing standards or manufacturing realities. Without the ability to flexibly capture and codify internal best practices directly within the MBD environment, organizations struggle to standardize workflows and ensure repeatable project success across different teams.
• Automation: Engineers spend hours manually detailing models because legacy tools lack the ability to create and deploy custom CAD features with Product and Manufacturing Information (PMI) built right in, forcing them to repeat the same tedious annotation steps for every new part rather than automating the workflow.
• Integrations: MBD is supposed to serve as the foundational data layer for the entire enterprise. But if the CAD data cannot seamlessly flow into PLM, ERP, and MES systems via modern, robust APIs, the "model-based" workflow hits a brick wall. Without automated, system-to-system connectivity, organizations are forced to fall back on error-prone manual data entry and disconnected 2D PDFs.

A New Paradigm: Why Onshape Gets MBD Right

Inspection Table and Annotations shared as an Onshape Publication.

To succeed, MBD requires a fundamental shift away from legacy, file-based architectures. With Onshape, MBD is a natural part of everyday workflows, featuring sketches and features that are tolerance-aware at their core.

Because it is a cloud-native platform, Onshape delivers unprecedented accessibility and true anytime access. Through view-only support for light users and Onshape Publications, the 3D model acts as a single source of truth available anytime, anywhere. Rather than relying on static views, the shop floor can dynamically filter the exact model data they need on any device.

Onshape also reimagines ease of use and customization. Organizations can define and store default tolerances in company libraries, natively capturing internal best practices and eliminating repetitive, manual baseline inputs.

Through automation, custom CAD features can actively write MBD data to speed up the detailing process. Finally, Onshape provides seamless enterprise integrations via robust APIs and native STEP AP242 exports, ensuring your MBD data flows effortlessly into PLM, ERP, MES, and downstream CAM and CMM systems.

The industry has waited long enough. By making MBD highly accessible, customizable, and connected, Onshape finally delivers on the promise of a true single source of truth.

(Disclaimer: For MBD annotations to appear in the above examples, you need to have an Onshape account, then open the Inspection Table. See instructions.)