Text-to-CAD vs Drawing-to-CAD: Two Kinds of AI CAD Compared

What is being compared

Text-to-CAD takes a description in words, such as “a machined aluminium part 120 mm wide with a central boss, two pockets, 3 mm fillets and four M6 tapped holes”, and generates a 3D model. Some tools write a parametric feature sequence or a CAD script and run it to get an exact solid; others generate a mesh directly. The prompt is the only specification, and it is almost always incomplete.

Drawing-to-CAD takes an existing 2D engineering drawing, usually a PDF, and builds the 3D model the drawing defines. The drawing was made to be complete: views, dimensions, tolerances, notes and a title block. The work is to read it correctly, and to notice where it is not complete enough to build from.

Both sit under the AI CAD label, alongside assistants inside CAD systems and models that generate geometry from CAD data. The AI CAD overview maps the whole category, and the guide What is AI CAD? explains each kind. This page compares the two that turn an input into a part.

Text-to-CAD

What it does well

• A first shape, fast. A described part can appear in seconds, which suits concepts, fixtures, enclosures and quick what-ifs.
• No drawing needed. It fits work that starts from an idea rather than from a released design.
• Iteration in words. For simple parts, changing “four holes” to “six holes” and generating again can be quicker than editing a sketch.

Its risks

• The gaps are filled for you. A prompt never states every dimension, tolerance and edge treatment, so the generator supplies them. The model looks complete either way, and nothing in it marks which values were asked for and which were chosen.
• No source to check against. With no drawing behind it, “correct” means what the person meant, which only that person can confirm, value by value.
• The output type varies. A mesh, or a solid made of approximated surfaces, can look right on screen and still be unusable for CAM or inspection. Check that the file is an exact B-rep solid before relying on it.
• Repeatability. The same prompt can give different geometry on different runs. Keep the model you checked, not the prompt.

Drawing-to-CAD

A worked example. A machined flanged bearing housing, drawn in three views and a section: a Ø52 H7 bearing bore, a bolt flange with 4X M8 tapped holes, two pockets and 2 mm fillets. Drawing-to-CAD has to read each callout into a requirement, tie the bore in the section to the circle in the top view, and ask about any value the views leave open. Complex parts: in development. Today TruePart builds one part family: rectangular plates with a centered bore and a hole pattern.

What it does well

• The specification already exists. Every value can be traced to a callout on the drawing, and a reviewer can check it there.
• Gaps are visible. Because the drawing is the authority, a value it does not state can be named as missing and asked about instead of being made up.
• It fits released work. Shops, buyers and engineers who receive drawings, rather than prompts, need a model of that part, not of a similar one.

Its risks

• Misreading. A dimension attached to the wrong feature, a Ø read as 0, or a missed count such as 4X gives a confident, wrong model. Scanned drawings make this more likely.
• Silent fills. A tool that never asks is filling missing values itself: the text-to-CAD risk again, with a drawing as cover.
• Narrow scope. Each part family and drawing convention has to be handled on purpose. Ask which are handled today, and test them.

Side by side

Where review is required in both

Neither approach removes the engineer. In text-to-CAD, a person has to check every value that matters against what they meant, because nothing else records it. In drawing-to-CAD, a person has to approve the values that were read and answer the questions about the values that were not, before anything is built for manufacture. In both, a STEP file is an exchange of geometry, not a release to manufacture: tolerances, material, finish and inspection still come from the drawing or the approved specification.

How to evaluate either kind

For a full test set, scoring and the questions to put to a vendor, see the evaluation criteria for AI drawing-to-CAD software.

Choosing between them

If the part does not exist yet and you want to see a shape quickly, text-to-CAD is the faster start, as long as someone dimensions and checks the result before it is used. If the part is already defined by a drawing, which is the normal case in quoting, purchasing, machining and legacy re-modeling, drawing-to-CAD is the approach that keeps the drawing as the authority. Many teams will use both: one to explore, the other to rebuild what has been released. The AI CAD generator guide walks through drawing-to-CAD step by step.