StepSTLTools
100% Client-SideWebAssembly CAD EngineZero Cloud Uploads.step & .stp

STEP & STP to STL Converter

Convert CAD models locally in your browser. Inspect geometry, verify mesh health, and export Binary STL.

CAD Conversion and Mesh Inspection Workbench

Drop .STEP or .STP files here

Single or Batch • 100% In-Browser Memory • Zero Uploads

📂 Browse CAD Files
ISO 10303Multi-File BatchMax 50 MB/file

Large CAD files (>50MB) are recommended for desktop workstations due to mobile browser memory limits.

Tessellation Parameters

Deflection Controls
📐 Deflection Tolerances(Draft: 0.5mm • Std: 0.1mm • Fine: 0.01mm)▼
Draft
0.50 mm
~46° deflection
Standard
0.10 mm
~29° deflection
Fine
0.01 mm
~11° deflection
CAD Workbench
ISO 10303 • WASM
Inspection Viewport
Orbit: DragPan: Right DragZoom: Scroll
Inspection ViewportStandby • Load a STEP or STP file to verify 3D mesh geometry
01
Privacy First

100% Client-Side Privacy

Your CAD geometry never leaves your workstation. OpenCASCADE executes entirely inside a browser-local WebAssembly sandbox.

02
3D Inspection

Model Inspection

Inspect the exact tessellated mesh buffer in 3D before exporting. Toggle wireframe rendering, coordinate axes, and reference grid.

03
Mesh Verification

Mesh Validation

Detect zero-area degenerate triangles, duplicate facets, and non-manifold edges to prevent 3D printer slicing failures.

Dedicated CAD Tools

ISO 10303 Standards
STEP to STL Converter.step
Optimized for standard .step CAD solids
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STP to STL Converter.stp
Optimized for .stp abbreviated files
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Batch STEP to STL.zip
Convert multiple files with 1-click ZIP
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3D Print Pre-Flight FitSlicer Fit
Build volume & orientation audit
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CAD Mesh RepairWatertight
Auto-heal normals & slivers
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STEP to OBJ Converter.obj
Convert B-Rep boundaries to Wavefront OBJ format
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In-Browser CAD Architecture & Tessellation Specifications

Technical overview of client-side WebAssembly execution, ISO 10303 B-Rep tessellation, and 3D printing mesh validation.

Browser-Local Processing & Data Privacy

Conventional online CAD converters upload source files to cloud servers where geometry is processed and stored remotely. StepSTLTools executes OpenCASCADE Technology (OCCT) compiled to WebAssembly (WASM) directly inside your web browser.

  • Zero Server Uploads: Files are read via transferable ArrayBuffer memory directly on your workstation. No CAD data is transmitted over the network.
  • Isolated Worker Thread: Heavy C++ tessellation calculations run inside a background Web Worker, ensuring fluid UI interaction during conversion.
Client-Side Processing: All B-Rep parsing, face stitching, and mesh generation occur strictly within the browser tab's allocated memory.

B-Rep to STL Tessellation & Deflection Controls

STEP and STP models store continuous mathematical surfaces (NURBS, analytic cylinders, planes). Because manufacturing software and 3D slicers require faceted polygon meshes, surfaces must be tessellated into planar triangles:

  • Linear Deflection (Chordal Deviation): Defines the maximum geometric distance between the true curved B-Rep surface and any approximating facet.
  • Angular Deflection: Governs normal angle deviation between adjacent triangles, refining curves and fillets.
Calibrated Presets: Standard (0.10mm) balances smooth curved surfaces with manageable file sizes. Fine (0.01mm) is recommended for high-resolution resin prints and precision mechanical fits.

3D Slicer Preparation & Unit Normalization

Standard STL files contain no unit metadata. When imported into slicing engines (such as Bambu Studio, PrusaSlicer, Cura, or OrcaSlicer), coordinates are assumed to be in millimeters:

  • Scale Protection: The OpenCASCADE CAD engine interprets ISO 10303 unit declarations and automatically normalizes coordinates to millimeters, preventing 25.4× scale discrepancies.
  • Mesh Health Validation: Built-in checks verify facet topology, identifying degenerate zero-area triangles, duplicate faces, and open boundary edges.
Binary STL Output: Exports standard 84-byte header + 50-byte per triangle binary format for direct slicer compatibility.

Dedicated Tools & Format Support

Choose the dedicated workflow tailored to your CAD source assets and production requirements:

  • STEP to STL Converter: Optimized for standard multi-body .step CAD solids with complete tolerance calibration and benchmark metrics.
  • STP to STL Converter: Tailored for .stp exchange files, including detailed troubleshooting for external assembly references and open surfaces.
  • Batch STEP to STL Queue: Queue multiple CAD files for sequential browser-local conversion with bundled ZIP archive downloads.
Supported Schemas: Full compatibility with ISO 10303 AP203 (configuration controlled 3D), AP214 (automotive mechanical design), and AP242 (managed model-based 3D engineering).

B-Rep Surface Mathematics & Polygon Repair Architecture

Standard interchange formats like STEP (ISO 10303) store exact mathematical geometry. Understanding boundary representation fundamentals ensures your physical 3D prints match original design intent.

Boundary Representation (B-Rep) Topology

Unlike mesh files that only know flat triangles and vertex coordinates, B-Rep models maintain strict topological relationships: Vertex → Edge → Wire → Face → Shell → Solid. Each face is bounded by trimmed NURBS (Non-Uniform Rational B-Splines) curves evaluated with double-precision floating-point polynomials.

When adjacent B-Rep surface patches do not share identical boundary curves within 0.001mm tolerance, translation algorithms generate disconnected edge seams. Our in-browser OpenCASCADE WebAssembly engine executes automated vertex welding to bridge tolerance gaps without manual stitching.

Watertight Manifold Topology for Additive Slicing

3D printer slicers (Bambu Studio, PrusaSlicer, OrcaSlicer, Cura) rely on the Jordan curve theorem during 2D layer slicing. For every horizontal cutting plane, the slicer computes ray-triangle intersections to determine interior infill boundaries versus exterior shell perimeters.

If a model contains inverted facet normals, open boundary holes, or internal intersecting walls (non-manifold geometry), the parity calculation inverts: solid plastic prints as hollow cavities and infill is generated in thin air. Pre-validating mesh watertightness eliminates 99% of print failures.

Sagitta Deviation & Chordal Deflection Math

Converting a continuous cylinder or sphere into planar facet triangles introduces geometric error known as sagitta (chordal deflection). The maximum deviation distance is given by e = R × (1 - cos(θ/2)).

Our converter allows precise linear deflection limits down to 0.005 mm (5 microns). This eliminates faceted cylinder flats on cylindrical bearing fits without inflating file size beyond the processing limits of modern 32-bit motion controller boards.

Zero-Egress Client-Side WebAssembly Architecture

Proprietary industrial CAD models, military components under ITAR compliance, and unpatented mechanical inventions require absolute data security. Most web converters upload files to remote servers where files are stored in cloud storage buckets.

StepSTLTools executes the full OpenCASCADE C++ geometric modeling engine compiled directly into WebAssembly (Wasm). All parsing, facet generation, and binary STL encoding occurs exclusively in your workstation's CPU and RAM.

Technical Documentation

Featured Engineering Guides

View All Guides →
CAD Repair

Fix Non-Manifold STEP & STL Errors

Eliminate open boundary holes, inverted normals, and unsliceable geometry for 3D printing.

Read guide →
Meshing Physics

Chordal Deviation & Tessellation

Master linear and angular sagitta parameters to balance curve smoothness with file weight.

Read guide →
Tool Guide

Best Free STEP File Viewers

Inspect and measure 3D models without $4,000/yr licenses. Local Wasm vs cloud security.

Read guide →

CAD Conversion, Repair & Analysis Suite

Client-side WebAssembly tools for STEP and STP files. Instant 3D processing, zero server uploads.
Convert STEP to STL.step to .stl

Tessellate standard .step CAD solids into clean, high-resolution binary STL files.

Open tool→
Convert STP to STL.stp to .stl

Full support for aerospace & industrial AP203/AP214/AP242 STP assemblies.

Open tool→
CAD Mesh Repair & Normal HealingWatertight

Auto-repair inverted facet normals, cull degenerate slivers, and make STL watertight.

Open tool→
STEP File Analyzer & CaliperB-Rep Inspection

Extract volume, surface area, bounding box calipers, and open edge diagnostics.

Open tool→
Batch STEP to STL ConverterMulti-File .zip

Queue multiple CAD files and download converted STL models in a single ZIP archive.

Open tool→
STEP to 3D Print Slicer PrepBambu & Prusa

Verify build plate envelope fits and optimize orientation for Bambu Studio, PrusaSlicer, and Cura.

Open tool→
STEP vs STL Comparison GuideEngineering Guide

Deep dive into mathematical B-Rep curves vs planar triangular facets for additive manufacturing.

Open tool→

Frequently Asked Questions

How does StepSTLTools protect confidential CAD data?

Unlike conventional converters that upload files to external servers, StepSTLTools executes OpenCASCADE locally in your browser via WebAssembly. Your engineering files never leave your device.

What CAD formats are supported?

Standard ISO 10303 STEP (.step) and STP (.stp) application protocols including AP203, AP214, and AP242 with output to compact Binary STL or plaintext ASCII STL.

Can I inspect the tessellated mesh before downloading?

Yes. The integrated Three.js viewport provides interactive orbital rotation, wireframe overlays, coordinate axes, and mesh quality diagnostics.