Large STEP assemblies no longer hang in 3D CAD Converter 1.0.21

September 2026 • ContentaSoft Team

3D CAD Converter 1.0.21 shipped on 22 September 2026. Big STEP files open and convert faster, and the one case where a conversion could run for more than half an hour without finishing is fixed. For normal files the output is byte-for-byte the same as in 1.0.20: only the waiting changed.

Every number below was measured on real files on one Windows test PC, running the 1.0.20 and 1.0.21 builds on the same files one after the other.

Before and after, measured

Meshing itself is about 30 % faster: 227 → 158 ms on a small part, 1,855 → 1,238 ms on the 19 MB assembly. A whole conversion gains less, because reading a large STEP file still takes 10 to 15 s of the 12 to 18 s: converting the 19 MB assembly to GLB went from 31.0 to 27.2 s of CPU time.

What changed

• STEP files are meshed once. The engine turned every STEP surface into triangles twice and threw the first result away. It now does it once. The triangles are identical, checked on 17 files in 7 output formats.
• The preview reads a STEP file once. Opening a preview started the engine three times: for the geometry, the file information and the parts list. It now runs once and keeps the result, so opening the same file again does not read it again.
• A new OBJ writer. OBJ export no longer goes through the general-purpose 3D library. The new writer produces the same bytes (91 of 91 test files identical) in about a quarter of the time: 19.8 → 4.8 s of CPU time on the 28 MB STL.
• Thumbnails really use Draft quality. They asked for Draft but got Standard meshes. The thumbnail of the 19 MB assembly now uses 134,000 triangles instead of 486,000.

Bill of Materials: one row per part, with a quantity

Engineers use the BOM export to count parts before a quote or an order. Up to 1.0.20 an assembly collapsed into its top node: our 19 MB test assembly, with 65 solids, came out as a single row.

In 1.0.21 each unique part gets one row with a Quantity column. Quantities multiply through sub-assemblies: a bolt used 4 times in a sub-assembly that appears twice counts 8. The same assembly now lists 47 parts whose quantities add up to 65.

• The CSV export has a Quantity column right after the part name, followed by the solids, faces and size of one copy.
• The parts panel in the 3D preview has a Qty column. On Windows it often stayed empty before, because file paths broke the parts data. That is fixed.
• The JSON export is valid JSON: Windows paths and part names are escaped.

No more endless meshing at Fine quality

Some STEP assemblies never finished at Fine quality. We traced it to single faces. In our test assembly, one curved face has an outline with a 0.0005 mm gap where two edges cross. The mesher does not fail on it: it keeps working, with no progress and no way to cancel. A twin face without the gap meshes in 79 ms.

1.0.21 puts a 30-second limit on meshing for previews and for Fine-quality conversions:

1. If the mesh finishes within 30 seconds, nothing changes: same triangles as before.
2. If the file has faces with open outlines, a copy with those gaps closed is meshed at the same time and used when the 30 seconds run out. It keeps full Fine detail: 339,392 triangles for the 4 MB assembly.
3. If that copy cannot be meshed either, the file is meshed at Standard quality instead.
4. When step 2 or 3 happens, the file's row in the list shows a note that says so. The command line prints the same note.

A model without damaged faces is never made coarser, however long it takes. Standard, Draft, custom settings and UltraFine are not limited: at UltraFine both test assemblies finish on their own in 85 and 104 seconds, and a 30-second limit would have dropped them to Standard.

With the limit, the 4 MB assembly converts to STL at Fine in 33.5 seconds and the 19 MB assembly in 85.2 seconds. Before, neither conversion finished.

Smaller fixes

• The conversion engine no longer crashes silently on a bad file. An invalid or missing STEP file, or a mistyped number on the command line, now ends with an error message that names the problem.
• The preview now shows file information for IGES files too. Before, stray messages from the CAD kernel made that information unreadable for the app.

How to get 1.0.21

Already installed? Start 3D CAD Converter. A banner shows that version 1.0.21 is available; click it to download the update.

New to 3D CAD Converter? The free trial gives you 10 conversions on your own files, with no account or credit card. After that it is a one-time licence, no subscription. Download the free trial

Learn more: High-quality STEP to STL  ·  STEP file won't open?