An STL stores triangles approximating a surface. A converter can write that geometry into a STEP file without knowing the original sketches, constraints, dimensions, features or design sequence. Check the resulting content, not just its extension.
Download the English project worksheet. Open it as UTF-8 CSV, replace the guide context with your project inputs and record observations separately from acceptance decisions. Blank cells do not indicate a passed check.
Establish why the recipient needs STEP
Do they need a file their software opens, inspectable facets or editable design features? Direct conversion may be sufficient for the first two if the recipient accepts that content. For dimension-driven changes, remodelling from design intent is often the clearer route.
Inventory the source before converting
First inspect the STL. Record filename, revision, hash, triangles, shells and dimensions, with confirmed units and closure. A converter can carry a source defect into the result without an obvious error.
If only one dimension needs changing, compare a bounded STL edit with remodelling. A different container is not always necessary; what matters is whether the change and preserved features can be verified.
Understand the missing design information
A triangle gives three vertices. It does not say whether it once belonged to a cylinder, extrusion, fillet or parameter-controlled feature. Twelve triangles forming a block cannot reveal the original sketch or feature sequence. “STEP created” therefore does not mean “original CAD restored”. Associations and design history do not automatically return.
Inspect the controlled conversion example
| Check | Source STL | Converted STEP |
|---|---|---|
| Dimensions | 40 × 20 × 10 mm | 40 × 20 × 10 mm |
| Triangles | 12 | Reopened as 12 triangular meshes |
| Representation | Closed mesh fixture | Compound of 12 planar faces |
| Sketches and constraints | Absent | Not recovered |
| Certified solid | Not claimed | Not claimed |
The conversion used replicad 1.1.0 and replicad-opencascadejs 1.1.0, with readback through occt-import-js 0.0.23. That reader also uses the OpenCascade family: it is a second reader, not an independent CAD kernel. This is digital file evidence for one simple block, not a physical print or a result for arbitrary complex meshes.
Open the source STL and faceted STEP locally. You do not need to execute a downloaded website script to inspect them.
Audit the conversion and make an explicit decision
Keep the original. Record converter, version and settings, then reopen the export in a second reader. Compare dimensions, object or shell count, orientation and facets. Save hashes, observations and the decision. A file that opens but changes size, loses parts or develops unexpected holes is a no-go until units or topology are resolved.
Decide whether facets or remodelling meet the need
Accept faceted STEP only when the recipient explicitly can use it and the geometry checks pass. Choose remodelling when diameters, radii, walls or linked features need reliable editing, or the recipient needs a suitable solid with editable features. Record expected content, actual result and the reason for accepting or rebuilding.
Request the editability you actually need
If the checked faceted STEP is sufficient for inspection, a new parametric design is not automatically necessary. For later changes to diameters, walls or connected dimensions, send the STL and a marked sketch to 3D modelling. Agree which features must be editable and which source and exchange files are delivered. Do not request “recovered original CAD” when that source is missing.
If the rebuilt design will be printed, check its STEP-to-STL export, especially curved mating features.