⚙️ CAD Scripting & Automation: Macros, APIs, and Generative Design for Engineers

Why Automate CAD Work at All

Most CAD work is genuinely one-off design judgment: deciding how a bracket should be shaped, how a cable should route around an obstruction, or how a mechanism should articulate. None of that is a good candidate for automation, because the actual bottleneck is engineering judgment, not the mechanical act of clicking through menus. But a meaningful share of everyday CAD work is exactly the opposite: repetitive, mechanically consistent, and differing only in input values — generating a family of similar drawings, exporting a folder of assemblies to a neutral format for a supplier, renaming hundreds of files to match a new part-numbering scheme, or applying the same title-block update across every drawing in a project. This is precisely the kind of work that CAD scripting and automation exists to eliminate, freeing engineering time for the judgment-driven work that actually needs a human.

Macro Recorders: The Easiest On-Ramp

Every major MCAD package — SolidWorks, Inventor, Fusion 360, and others — includes some form of macro recorder, a tool that watches a user perform a sequence of actions in the normal interface (creating a sketch, applying a fillet, changing a dimension, exporting a file) and automatically generates working script code that reproduces that exact sequence. This is the lowest-friction entry point into CAD automation available, because it requires no prior programming knowledge at all to produce a first working script — a user simply turns on the recorder, performs the task once by hand the normal way, and stops recording.

The recorded script is rarely useful completely unmodified, however. A macro that fillets a specific edge on a specific part typically hardcodes that part's file path and that edge's internal reference, so running the raw recording again only ever repeats the exact same operation on the exact same file. The practical next step, requiring only modest scripting literacy rather than formal programming training, is editing the recorded code to replace hardcoded values with variables — for instance, wrapping the recorded steps in a loop that iterates over every file in a folder, or replacing a hardcoded fillet radius with a variable read from a spreadsheet — which turns a single-use recording into a genuinely reusable automation tool. This "record, then edit" workflow is how the overwhelming majority of practical, individually-built CAD automation gets written, and it is well within reach of an engineer with no formal software development background.

Native APIs: SolidWorks, Fusion 360, and Inventor

Beyond simple macro recording, each major CAD platform exposes a full Application Programming Interface (API) — a structured set of programmatic commands that let external or embedded code control essentially everything the graphical interface can do, and often more, including things with no direct menu equivalent at all.

SolidWorks exposes its API primarily through VBA (Visual Basic for Applications, the same macro language embedded in Microsoft Office) for quick, embedded scripts, and through a full COM-based API accessible from more capable languages like C# or Python for larger automation projects, such as standalone applications that batch-process files without SolidWorks's interface even being visibly open.

Fusion 360 takes a cloud-native, Python-first approach: its API is accessed by writing Python scripts (or add-ins, which are persistent scripts with their own UI elements) in an integrated script editor, giving direct programmatic access to sketch and feature creation, the parametric timeline, assembly structure, and export functions. Because Python is a widely-used general-purpose language well beyond CAD, engineers who already know some Python from other contexts (data analysis, general scripting) find Fusion 360's API comparatively approachable, though it does still require genuine programming literacy rather than the simplified rules-based approach some other platforms offer.

Inventor offers two distinct automation paths that suit different needs. Its full API, similar in spirit to SolidWorks's, is accessible via VBA or .NET languages for deep, code-first automation. But Inventor is also well known for iLogic, a rules-based automation layer built directly into the modeling interface, using simplified syntax (based on VB.NET but presented through an accessible rules editor rather than a separate coding environment) specifically aimed at parametric design logic — for example, a rule that automatically suppresses a mounting-hole feature, or swaps in a different fastener component, based on a configuration parameter the user selects from a dropdown. iLogic sits deliberately between a full API and a plain macro recorder: more powerful and reusable than a raw recording, but far more approachable than writing a standalone program against the full API.

Common, High-Value Automation Patterns

A handful of automation patterns recur across nearly every engineering team that adopts CAD scripting, because they map directly onto the most tedious, most repetitive categories of CAD work.

Batch export and format conversion. A script iterates over every file in a folder (or every configuration within a multi-configuration part) and exports each to a target format — STEP for a supplier, PDF for a drawing package, STL for 3D printing — applying consistent export settings across all of them, which a human doing this by hand would inevitably apply inconsistently across dozens of files.

Design table / parameter-driven part families. Rather than modeling twelve nearly-identical bracket sizes as twelve separate files, a script (or a built-in design-table feature, which is itself a lightweight form of automation) drives a single parametric model through a spreadsheet or table of dimension values, generating the full family of sizes from one master model and one data table, which also means a single design fix only needs to be made once rather than replicated across twelve files.

Drawing and title-block automation. A script populates drawing title blocks, revision tables, and balloon/reference-designator numbering automatically from the model's own metadata (part number, description, material, mass properties), eliminating both the manual data entry and the class of errors where a drawing's title block silently drifts out of sync with the actual model it depicts.

Custom validation and standards checking. A script scans a model or an entire assembly for rule violations before release — unfilleted sharp internal corners, missing material properties, drawing views without dimensions, non-standard fastener sizes — catching the kind of standards violations a design review would otherwise need to find by eye, and catching them earlier and more consistently.

How This Connects to Generative Design

Ordinary CAD scripting and generative design both use code and rules to create or modify geometry instead of manual clicking, but they sit at fundamentally different points on the automation spectrum. A recorded macro or a scripted batch process is deterministic and human-directed: it automates a specific sequence of modeling steps a human already knows how to perform by hand, executing that known design intent faster and more consistently than manual repetition would, but a human still fully decides what the final geometry should look like before the script ever runs.

Generative design inverts that relationship. Instead of specifying the geometry, an engineer specifies the problem — the applied loads and constraints, the manufacturing method (machining, casting, additive manufacturing), allowable material, and a design space or "keep-out" envelope — and the software's optimization algorithms then explore a vast space of candidate geometries, running structural or performance simulations against many of them, to propose shapes that meet the specified performance target with minimum mass or material use. These results are often organic, topology-optimized forms that a human designer likely would not have arrived at through direct manual modeling. Generative design tools are increasingly built into mainstream MCAD platforms (Fusion 360's generative design workspace is a widely used example), and they typically demand substantially more computational solving time than a simple recorded macro or batch script, since evaluating many candidate geometries against real physics is inherently far more expensive than replaying a fixed sequence of modeling operations.

Getting Started Without Over-Investing

The practical path into CAD automation almost never starts with learning a full API from scratch. It starts with recording a macro for the single most tedious, most frequently repeated task in a specific workflow, examining the generated code, and making one small, useful edit — hardcoding one value out and replacing it with something that varies. That single successful edit is usually enough to reveal whether a given repetitive task is genuinely worth automating further. Not every repetitive task is: a task performed only occasionally, or one where every instance differs enough that a generic script would need constant rewriting, may simply not be worth the setup investment. The tasks worth genuinely investing in — writing a proper standalone script against the full API, building a reusable design table, or eventually exploring generative design — are the ones repeated often enough, and consistently enough, that the time saved over dozens or hundreds of repetitions clearly outweighs the time spent building and maintaining the automation in the first place.