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CAD & Tools

Which design software to use for printable parts, how to fix broken meshes, and which file format to send to the slicer (or to another person). Licence terms change — the notes below were checked in October 2026; confirm on the vendor's page before relying on them commercially.

CAD comparison

Tool Cost / licence Parametric? Platform Learning curve Best for Export (3D)
FreeCAD 1.x Free, open source (LGPL-2.1) Yes — sketches + feature history Windows, macOS, Linux Steep Mechanical parts, fully offline/open workflow STEP, IGES, STL, OBJ (+ many more)
Autodesk Fusion Free Personal Use tier (limits below); paid subscription for commercial Yes — history-based, plus direct/T-spline modelling Windows, macOS Moderate Mechanical parts and assemblies; most tutorials online STEP, STL, 3MF, OBJ, F3D (personal tier)
Onshape Free plan is non-commercial and every document is public; paid plans for private docs Yes — history-based, cloud Web browser (plus mobile apps) Moderate Mechanical parts, collaboration, any OS incl. Linux/Chromebook STEP, Parasolid, IGES, STL, 3MF, OBJ
OpenSCAD Free, open source (GPL-2) Yes — by code (CSG script) Windows, macOS, Linux Moderate (easy if you code) Simple parametric/customisable parts, "configurator" models STL, 3MF, AMF, OFF — mesh only, no STEP
build123d / CadQuery Free, open source (Apache-2.0) Python libraries on the OCCT kernel Yes — by code, true B-rep Anywhere Python runs Steep (Python + CAD concepts) Scripted, version-controlled, generated parts STEP, STL, 3MF, plus glTF/OBJ/DXF/SVG (varies by library)
Blender Free, open source (GPL) No — mesh modelling (modifiers/geometry nodes are procedural, not a CAD history) Windows, macOS, Linux Steep Sculpting, organic shapes, figurines, texturing STL, OBJ, PLY, glTF and more
Tinkercad Free (Autodesk account) No — combine primitives Web browser Very easy Beginners, kids, quick simple parts STL, OBJ and others

Fusion Personal Use limits

Autodesk's free tier is for home-based, non-commercial use by people generating under US$1,000 a year from it. It is limited to 10 active editable documents (others are stored read-only until you swap them in), drops some commercial translators and advanced CAM, and has community-only support. STEP, STL, 3MF and OBJ export remain available. Check Autodesk's current terms — they have changed several times.

Onshape free = public

On Onshape's free plan anyone can find and copy your documents. Don't put anything confidential, or anything you intend to sell, in a free account.

Notes on each

  • FreeCAD — 1.0 (November 2024) largely tamed the long-standing topological naming problem (references breaking when you edit an earlier feature) in Sketcher and PartDesign, and added a built-in Assembly workbench; 1.1 (March 2026) added transparent Part Design previews and on-model draggers for fillet/chamfer. Still the most capable fully free/offline option, with the steepest learning curve.
  • Fusion — the de-facto hobby standard: the most YouTube tutorials, good sketch constraints, assemblies and joints, built-in mesh tools. Cloud account required.
  • Onshape — the same history-based workflow as Fusion but runs entirely in the browser, so it works on Linux and low-power machines. Built-in version control and branching.
  • OpenSCAD — you write a script (cube, cylinder, difference()…) and it renders a mesh. Excellent for parametric boxes, spacers and customisable models; awkward for fillets and organic shapes. Output is a mesh, so you can't hand someone a STEP file.
  • build123d / CadQuery — Python CAD on the same OpenCASCADE kernel as FreeCAD. You get real B-rep solids (proper fillets, STEP export) and code you can diff, test and keep in git. build123d is the newer, more "Pythonic" API and derives from CadQuery.
  • Blender — a mesh/sculpt tool, not CAD. Great for organic forms; poor for dimensioned mechanical parts. Two add-ons help printing: 3D-Print Toolbox (manifold checks, wall thickness, overhangs, export) and CAD Sketcher (constraint-based 2D sketching that can be extruded non-destructively). Blender's default unit is the metre — set the scene to millimetres (or check scale on export) or parts arrive 1000× too big or small.
  • Tinkercad — drag-and-drop primitives in the browser. The fastest way to start; you'll outgrow it as soon as you need precise fillets or editable dimensions.

Which should I use?

Tinkercad. Free, runs in a browser, nothing to install. Move to Fusion, Onshape or FreeCAD once you want dimensions you can change later.

Fusion (if the personal-use terms fit), Onshape (if public documents are fine, or on Linux) or FreeCAD (if you want fully free and offline). All three are parametric: change one dimension and the model rebuilds.

OpenSCAD for simple customisable models; build123d/CadQuery when you want real fillets, STEP output and code under version control.

Blender (sculpt, then check with 3D-Print Toolbox). For hybrid parts — an organic shell on a mechanical mount — model the mount in CAD, export it, and combine in Blender or the slicer.

Small tweaks: the slicer (cut, add negative volumes, scale). Bigger changes: Fusion/FreeCAD mesh-to-solid tools work on simple meshes, but it's usually faster to remodel from measurements. If you can get the STEP file, ask for it.

Design for the process

Whatever tool you use, apply the rules in Design for Printing — tolerances, overhangs, orientation — before you export.

Mesh repair

Slicers need a watertight (manifold) mesh: every edge shared by exactly two faces, normals pointing outward, no self-intersections. Exports from CAD are usually clean; downloads, scans and Blender models often aren't. Typical symptoms are missing layers, unexpected holes or "lids" in the sliced preview — see Troubleshooting.

Tool Status (2026) Notes
Slicer built-in repair (PrusaSlicer, Bambu Studio, OrcaSlicer) Current All auto-repair simple errors on import. The extra "Fix model" / "Fix by Netfabb" button uses Microsoft's Windows repair API, so it is Windows-only, and can take a long time on big meshes. Save/export the repaired model, or it is lost.
Microsoft 3D Builder Effectively gone Was a free Windows app with a one-click repair; it has been pulled from/broken in the Microsoft Store. Don't plan on it.
Autodesk Meshmixer Discontinued Still downloadable, but Autodesk says it is no longer in development or supported. Make Solid still rescues hopeless meshes (at a resolution cost). Many of its tools moved into Fusion's mesh workspace.
Blender 3D-Print Toolbox Current (Blender 4.2+ extension) Checks for non-manifold edges, intersections, thin walls and overhangs; Make Manifold fixes common faults. Free and cross-platform.
Fusion mesh tools Current Mesh workspace → Repair and mesh-to-B-rep conversion for simple meshes.
Netfabb Desktop product only The old free Netfabb online repair service was retired in 2021; Autodesk pointed users to Fusion's mesh repair. Netfabb itself is a paid professional package.
Online repair sites Varies Several free web services exist (Prusa's KB lists a couple); upload only models you're happy to share.

Fix it at the source

If you designed it, fix the model in CAD rather than patching the mesh — re-export with a finer tolerance, close open sketches, and union overlapping bodies before exporting.

File formats: STL vs 3MF vs STEP vs OBJ

Format Stores Units Colour / multi-material Slicer settings Editable as CAD?
STL Triangle mesh only (surface facets + normals) None — the slicer assumes mm No (non-standard colour hacks exist) No No
3MF Triangle mesh(es) in a ZIP of XML; multiple objects + build plate layout Yes (default mm) Yes — base materials/colours, per-object materials Yes — slicers save full projects (plates, modifiers, paint, profiles) in it No
STEP (.step/.stp) Exact B-rep solids (true curves and faces), assemblies Yes Face/part colours (AP214/AP242) No Yes — imports as solids in any CAD
OBJ Polygon mesh + optional UVs/normals; materials in a side .mtl file None Via .mtl/textures; some apps add vertex colours No No
  • Mesh vs B-rep. STL/3MF/OBJ store an approximation made of triangles; a circle becomes a polygon at export. STEP stores the actual cylinder, so it can be re-edited, re-meshed at any resolution, or machined.
  • Units. Because STL and OBJ have no units, a part modelled in inches or metres can arrive at the wrong scale — if it is tiny or 25.4× too big, that's why. 3MF and STEP carry units.
  • Slicer projects. A .3mf saved from PrusaSlicer, Bambu Studio or OrcaSlicer is a full project: plate layout, painted colours, modifiers and the print/filament/printer profiles used. Opening one may replace your settings with the author's — read the import prompt.
  • STEP in slicers. PrusaSlicer (2.5+), Bambu Studio and OrcaSlicer can import STEP directly and tessellate it on import, which avoids coarse STL faceting — the slicing itself still works on a mesh.

When to share which

You want to… Share
Let someone print it as-is 3MF (with sensible plate layout) — or STL for the widest compatibility
Share a multi-colour / multi-part print 3MF project
Let someone modify the design STEP (plus the native CAD file if they use the same tool)
Send to a machinist / CNC / injection-mould shop STEP
Textured or colour models for rendering/games OBJ (+ .mtl) or glTF

Sources & further reading