STEP to STL, tessellated at a tolerance you can see

Everything that made it CAD. A cylinder becomes strips, an edge becomes a chain of segments, the assembly tree becomes one lump, and the declared unit disappears — STL states none, which is why the same file can arrive at the wrong size in the next program. The geometry that survives is an approximation, chosen at a tolerance. That is not damage: a printer needs triangles and cannot use surfaces. It is simply one-way, which is why keeping the original STEP matters.

Relative to the part rather than absolute, which is the difference between a converter that works on one size of thing and one that works on all of them. The chord deviation is held to roughly a thousandth of the model's largest dimension, so a hole in a 20 mm bracket and the same hole in a 2 m frame both come out with a sensible number of segments. A fixed tolerance either makes small parts blocky or turns large ones into files a slicer chokes on.

No, and that is unusual. Reading STEP properly means evaluating NURBS surfaces, trimming them against their real boundary curves and triangulating the result in parameter space, which is why almost every browser converter either uploads your file or ships tens of megabytes of WebAssembly. The reader here was written for this site and runs as plain JavaScript. It is checked against OpenCascade on eleven fixtures — face counts match exactly and volumes land within 0.7%, the residual being inscribed tessellation rather than error.

Yes. Components carry their own placement transforms and those are applied, so the parts arrive positioned as they were authored rather than piled on the origin. The names are read too, and shown in the panel — but they cannot go into an STL, which has no place for them. If you need the parts to stay separate and named, convert to OBJ instead.

The panel counts them rather than hiding them. A face fails when its boundary cannot be resolved into loops that close in parameter space — usually a trimming curve that does not quite meet its neighbour, which is common in files exported through several packages. The rest of the model is unaffected, and a handful of failures out of hundreds of faces normally leaves a printable result. If most of them fail, the file is damaged and no converter will do better without repairing it first.

No. The parsing, the surface evaluation, the tessellation and the STL writing all run in this tab. That matters more for STEP than for most formats: a STEP file is usually somebody's actual product, and the commercial converters that ask you to upload one are asking for the most sensitive file in the project.