STEP file to a 2D drawing your shop can actually build from

You have the model. The shop wants a drawing.

STEP is the universal handoff between CAD systems, which is exactly why it turns up in inboxes with no drawing attached. Opening it just to produce three views and a dimension set means finding a licence, waiting for it to load, and remembering which menu the drawing template lives in.

A real projection, not a viewport screenshot

Ortho2D reads the STEP through an OpenCascade reader, builds the geometry, then removes hidden lines by testing visibility per edge. The result is line work — vector, layered, exportable to DXF — not a raster picture of a viewport.

AP203, AP214, AP242 — what your file is actually carrying

STEP is not one format. AP203 carries geometry and assembly structure and nothing else. AP214 adds colour, layers and presentation data, which is why parts out of automotive CAD arrive looking the way their author saw them. AP242 merges the two and adds PMI: dimensions and geometric tolerances embedded as machine-readable annotation rather than as a picture.

Ortho2D reads the geometry from all three. It deliberately does not import PMI. Embedded annotation is attached to faces in three dimensions and rarely lands where a flat view needs it, so the dimensions on your sheet are measured from the solid itself. The practical consequence is worth knowing: a fully annotated AP242 model still receives Ortho2D's own dimensions, not the ones its author placed.

Why a solid draws better than a mesh

A STEP file is a boundary representation. A cylindrical hole is stored as a cylindrical surface with a radius, not as a ring of triangles pretending to be round. Nothing has to be inferred: the circle on your drawing is the circle in the model, at full precision, and the ⌀ callout is exact rather than fitted.

That difference shows up in three places in particular. Small holes survive at any size instead of degrading into visible polygons. Fillets and rounds keep their tangency, so an outline does not develop flats where a curve meets a face. And thin walls stay two edges apart, where mesh tolerance can otherwise collapse both surfaces onto a single line and quietly lose a feature.

Sections, and where you put the plane

You position one cutting plane in the 3D viewport — slide it along its normal, rotate it, flip which side survives — and every view on the sheet regenerates from the cut solid. Cut faces are hatched. Faces behind the plane are drawn as ordinary visible edges and left unhatched, which is the distinction most automatic sectioning gets wrong and the one a fabricator notices immediately.

A worked case: on a 60 mm bracket with a 6 mm slot whose floor sits 12 mm above the base, running the plane through the slot centre produces a section that dimensions the slot depth directly. Without it, the reader has to subtract two numbers off the elevation and hope they picked the right pair. The section is labelled A-A and the cutting plane is drawn on the parent view with standard arrow ends.

Projection and line weight, to standard

First-angle projection (ISO, usual in Europe and Asia) and third-angle (ASME, usual in North America) are both selectable, and the matching truncated-cone symbol is drawn into the title block so nobody has to guess which convention a sheet follows.

Line weights follow ISO 128-20, which pairs a wide and a narrow line in a two-to-one ratio rather than specifying absolute thicknesses. Ortho2D ships selectable groups starting at 0.25 / 0.125 mm, and applies the wide weight and the narrow weight to elements as below.