Choosing Modeling Software

Three kinds of modeling software

Modeling programs differ less by brand than by how they store a shape, and that decides what they are good at.

Kind	How it stores the shape	Strong at	Weak at
Solid (parametric) CAD	Exact surfaces built from sketches and features, with a history you can edit	Measured functional parts, fits, holes, threads, design changes	Organic, sculpted shapes
Mesh modeler	Vertices, edges and triangles or polygons	Sculpted and organic shapes, editing and repairing existing STL files	Precise dimensions and true curves
Beginner block tool	Simple shapes combined and subtracted	First designs, quick simple parts, teaching	Complex or precise parts

FreeCAD's documentation explains the split well. Meshes are simple data that are easy to create, modify and pass between programs, which is why animation and film tools favor them, but in engineering they cannot accurately define curved surfaces, so FreeCAD uses boundary representation (BRep) instead. For printing, everything ends as a mesh in the end; the question is where you want to do the design work. See Meshes, Manifolds and Normals for what that mesh must look like.

The programs most guides mention

Tinkercad (beginner, browser)

Prusa's guide to creating your own models calls Tinkercad the easiest way to start: an online editor that runs in a browser with no installation, free and easy to operate. You build parts by combining simple shapes. It exports OBJ, STL or GLTF for 3D printing, either the whole design or only the selected shapes; Tinkercad notes that all shapes are grouped as a single part on export.

Autodesk Fusion (parametric CAD)

Prusa lists Fusion as another popular choice, available for PC, Mac and iPad, more complex than Tinkercad but with official guides and video tutorials. Its thread tool is covered in Threads and Snap Fits and its mesh export settings in Converting CAD Models and Exporting for Printing. Check Autodesk's current license options for your use before you commit to it.

FreeCAD (parametric CAD, open source)

FreeCAD describes itself as a parametric 3D modeling application made primarily for mechanical design, for modeling with precision and control over modeling history. It is open-source software for Windows, Linux and macOS. Its PartDesign and Part workbenches are the usual starting points for solid parts, and its Mesh Workbench converts solids to meshes and evaluates and repairs meshes.

Blender (mesh modeling, open source)

Blender's manual calls it the free and open-source 3D creation suite, covering the whole 3D pipeline from modeling, rigging and animation to simulation, rendering and video editing, on Linux, macOS and Windows. For printing it is strongest at organic shapes and at fixing existing meshes, helped by the 3D Print Toolbox extension; see Repairing Broken Meshes. It is not a parametric CAD program, so exact fits are more work than in FreeCAD or Fusion.

Others

Prusa's list of further options includes OpenSCAD (free), DesignSpark Mechanical, SketchUp, Maya and 3ds Max. Each has its own license and file export options; check them before you choose.

Choosing for the job

You want to make	Start with
A bracket, enclosure, replacement part or anything that must fit something else	Parametric CAD (FreeCAD, Fusion or similar)
A figure, sculpture, character or organic decoration	A mesh or sculpting tool (Blender or similar)
A first simple design, a name tag, a classroom project	A block tool (Tinkercad or similar)
A fix to a downloaded STL	Your slicer first, then a mesh tool
Many versions of one part with different sizes	Parametric CAD, where dimensions drive the model

What to look for, whatever you choose

• Units you can set and export in millimeters, or 3MF export; see Model Scale and Units.
• Control over export resolution so curves come out smooth.
• A way to check meshes for holes and flipped faces, built in or as an add-on.
• A file you can keep editing. Save the native project, not just the STL; changing a design is far easier in its source file.
• Learning material. Official manuals and tutorials matter more than feature lists when you start.

A slicer is not a modeling program, but it is the last step for every design; CAD, Slicing and the Path to a Print explains how the two fit together, and STL, 3MF, OBJ, STEP and G-code which files pass between them.