What an AI CAD generator does with a drawing
A 2D drawing describes a 3D part in projections: a front view, a top view, a side view, sections and details, each with dimensions, tolerances and notes. A person reading it builds the part in their head and then in CAD, one feature at a time. An AI CAD generator automates that reading and building. Done well, it produces the model a careful CAD designer would, with a record of where each value came from. Done badly, it produces a model that looks right and is not.
Generators differ most in two places: how they read the drawing, and whether the geometry is built from approved values or generated directly by a model. The first decides how many values are right. The second decides whether you can tell which ones are.
From 2D drawing to 3D STEP, step by step
The steps follow one worked example: a machined aluminium manifold block, drawn in three views and a section, with two intersecting Ø10 bores, a pocket, 1 mm fillets and six M5 tapped holes. Complex parts: in development. Today TruePart builds one part family: rectangular plates with a centered bore and a hole pattern.
01 Classify the input
Is the PDF vector or a scan? One sheet or several? Millimetres or inches? A vector PDF with real text lets software read callouts exactly; a scan has to be recognized from pixels, and every value needs checking against the image. The vector versus raster guide shows how to tell.
02 Find the views
Identify each view, its projection, its scale, and the sections and details that belong to it. A feature drawn in two views is one feature: a circle in the top view and two hidden lines in the front view are the same hole. See first and third angle projection.
03 Read the callouts into requirements
Turn each dimension, callout and title-block field into a requirement with its value, tolerance, units and place on the sheet. On the example block: Ø10 THRU for each bore, 6X M5 with its thread depth, the pocket's depth and corner radius, R1 for the fillets, the material and the general tolerance. The hole callout guide lists what a hole callout can carry.
04 Ask about what the drawing does not state
Check every feature for size and location. On the example block, a bore position shown only by a centerline, a pocket with no depth or a chain of dimensions that does not add up becomes a question for the drawing owner, not a default. The missing dimensions checklist covers the common cases.
05 Approve the specification
A person reviews every requirement with its source, the answered questions included, and approves one revision. Nothing should be built before this point.
06 Build an exact solid
Build the B-rep from the approved requirements. A deterministic CAD engine executing a typed plan gives the same solid every time; a model that writes geometry or code directly needs its output checked like any other untrusted input.
07 Measure it against the specification
Check the envelope, volume, feature counts, positions and diameters of the solid against the approved requirements. This shows the solid matches what was approved; it cannot show that the approval was right. The verification guide lists the checks.
08 Export STEP, and keep the drawing with it
Export the solid as STEP for CAD, CAM and inspection, and as STL only where a mesh is wanted. A STEP file at nominal size is not a release to manufacture: send the drawing, or the requirements with their tolerances, alongside it.
Where AI helps, and where it should not decide
| Step | Where a model can help | What stays deterministic or human |
|---|---|---|
| Classify the input | Recognizing a scan, a rotated sheet, a title block | Refusing an input outside the tool's scope |
| Find the views | Proposing view boundaries and links between views | The projection and scales the drawing states |
| Read the callouts | Recognizing symbols and text on scans; proposing which feature a dimension belongs to | Recording exactly what the sheet states, with its source |
| Ask about gaps | Spotting values a feature needs that are not stated | The value itself: the drawing owner answers |
| Approve | Ordering the review by uncertainty | The approval: a qualified person |
| Build | Proposing a feature sequence for review | Executing it: a deterministic CAD engine |
| Verify | Nothing that replaces measurement | Measuring the solid against the requirements |
The pattern is the same throughout: a model can propose, and a person or a deterministic process decides. A generator that lets a model's output become geometry with no approval and no measurement in between gives you speed and takes away your evidence.
Which inputs work best
- Native vector PDF exported from CAD. The best case: exact lines and real text.
- DXF or DWG. Exact geometry, but often without a title block, or with dimensions as loose text. Check which formats a tool accepts.
- Scanned PDF or photo. Readable, with recognition errors that depend on the scan. Review every value.
- Hand sketch. Sketch-to-CAD tools can propose a shape from a sketch, but a sketch rarely states the dimensions a part needs, so most values will be the tool's choice.
The value no generator can supply
A drawing can omit a dimension, contradict itself, or cite a standard the shop does not use. A generator can point at the problem. Only the drawing's owner can decide the answer, and a STEP file built on a guessed value carries no mark of the guess.
For the wider category, from text-to-CAD to assistants inside CAD systems, see What is AI CAD? and the AI CAD overview.
What TruePart does today
TruePart follows this order: it reads the drawing, asks about every value it cannot prove, builds nothing until those are answered and the specification is approved, then builds the solid with a deterministic CAD engine and measures it before STEP and STL are exported. In the Technical Preview it reads native vector PDF drawings of one part on one sheet, in millimetres, and builds one part family: rectangular plates with a centered bore and a hole pattern. Current public demo: deterministic drawing reader. AI-assisted interpretation: in evaluation, not enabled in this preview. The checks measure the envelope, volume, hole count, and each hole at planned position and diameter; they do not check tolerance bands, material or manufacturability. Complex multi-view part families are in development and not yet offered. See AI drawing to CAD and PDF to STEP.
Questions
Can AI turn any 2D drawing into a 3D model?
Not reliably. Clean vector drawings of the part families a tool handles can be read well; scans, unusual conventions and parts outside its scope are where errors and silent guesses appear. A good tool stops or asks instead of inventing.
Is the generated 3D model editable?
A STEP file holds the solid's exact geometry but usually not a feature history, so it opens as a solid you can change with direct modeling. If you need a parametric history, test that export on its own.
How do I check a generated STEP model?
Open it in your own CAD system, confirm it is one closed solid in the right units, and compare its overall size, volume, feature counts, positions and diameters with the drawing.
Does a 2D to 3D generator read tolerances?
Some record them as data. A solid is normally built at nominal size, so tolerances have to travel with the drawing or the requirements, not inside the geometry.
Sources
- ISO 5456-2, Technical drawings: Projection methods, Part 2: Orthographic representations · ISOFirst- and third-angle projection, for finding the views.
- ASME Y14.5-2018, Dimensioning and Tolerancing · ASMEThe dimensions, tolerances and callouts a generator has to read.
- ISO 10303 (STEP), Industrial automation systems and integration: Product data representation and exchange · ISOSTEP as the exchange format for the exact solid.
What TruePart does today
- LimitComplex parts: in development.
- LimitToday TruePart builds one part family: rectangular plates with a centered bore and a hole pattern.
- TodayTruePart follows this order: it reads the drawing, asks about every value it cannot prove, builds nothing until those are answered and the specification is approved, then builds the solid with a deterministic CAD engine and measures it before STEP and STL are exported.
- LimitIn the Technical Preview it reads native vector PDF drawings of one part on one sheet, in millimetres, and builds one part family: rectangular plates with a centered bore and a hole pattern.
- TodayCurrent public demo: deterministic drawing reader.
- In evaluationAI-assisted interpretation: in evaluation, not enabled in this preview.
- LimitThe checks measure the envelope, volume, hole count, and each hole at planned position and diameter; they do not check tolerance bands, material or manufacturability.
- LimitComplex multi-view part families are in development and not yet offered.