FreeCAD: designing a parametric part for 3D printing

How a parametric part works

The FreeCAD manual explains parametric modeling with a plain example: the shape of a brick can be controlled by three parameters, height, width, and length. Those parameters are part of the object and stay modifiable at any time after it has been created. For a repair part, that is exactly what you need: if your first print shows a hole is too tight, you change one value and the model recalculates.

The FreeCAD website adds that all objects are natively parametric, that every change is recalculated on demand and stored in an undo stack, and that one object's properties can drive another object's properties. You can tie a wall thickness to a diameter, for instance, and adjust a single number.

Another point that matters for printing: everything you do in FreeCAD uses real-world units, from microns to kilometers, including inches. The manual suggests staying in MKS in the preferences to follow its examples. If you are still weighing software options, the free CAD for 3D printing page compares them before you commit to a workflow.

Finding your way around the interface and workbenches

FreeCAD groups its tools into workbenches, sets of toolbar buttons and menus organized by specialty. The manual compares them to a workshop where each trade has its own bench but everyone works on the same objects. The workbench selector is the most important control in the interface. For a mechanical part headed to a printer, PartDesign is the workbench the FreeCAD website associates with building objects from constrained sketches.

Three areas matter for this tutorial. The 3D view, where you select and manipulate geometry. The combo view on the left, whose Model tab shows the document structure and the properties of the selected object, split into Data (the geometry itself) and View (how it looks on screen). And the Tasks tab, where FreeCAD prompts you for values specific to the active tool, such as a length.

The manual also recommends opening the Report view, hidden by default, because it lists warnings and errors. That is invaluable when a sketch refuses to close or an operation fails. Screenshots and menu labels in the manual match an older release, so look for the equivalent in your version rather than the exact wording.

Step 1: draw and fully constrain the sketch

The FreeCAD documentation describes the basic PartDesign flow: create a Body, a container object that can hold 2D sketches and 3D geometrical features to build a solid shape, then create a new sketch, draw a closed wire in it, and extrude it with PartDesign Pad to create an initial solid. The FreeCAD website describes the sketcher as the main building block of the software, with a built-in constraint solver that lets you draw geometrically constrained 2D shapes. These sources do not prescribe the sketch plane: for a tab that lies flat, we suggest sketching on the plane matching the face that will rest on the build plate.

Take a deliberately hypothetical example: a 40 mm by 20 mm tab, 4 mm thick, with two 4.5 mm holes for M4 screws. Draw a rough rectangle without worrying about size yet, then add constraints: first the geometric relationships between segments and to the origin, then the dimensions (length, width, hole diameter, hole-to-edge distance). The exact constraint names depend on your version; the sources used here document the solver and the principle, not each button. The goal is a fully constrained sketch, where every element is pinned by a dimension or a relationship.

This discipline feels tedious the first time, but it is where parametric design earns its keep: when every element is pinned by a dimension or a relationship, changing one value produces the change you expect, without leaving the solver any undefined freedom. For this example, place the two circles in the initial sketch before extrusion. Then inspect the solid and the sliced preview to confirm the intended openings; adding another Pad is not a hole-cutting operation.

Step 2: add volume and name your parameters

Close the sketch and apply PartDesign Pad, the tool the FreeCAD documentation describes for extruding a sketch into an initial solid. The Tasks tab asks for a length: enter your part thickness, 4 mm in our example. You now have a solid whose sketch and length remain editable properties. Double-clicking the item in the Model tab reopens the task panel so you can change the value, as the manual notes for most tools.

To centralize dimensions, the FreeCAD documentation describes the Spreadsheet workbench: data in spreadsheet cells may be used in CAD model parameter expressions, gathering the values in one place, and changes in the spreadsheet propagate throughout the model. Create a sheet, enter each value immediately followed by its unit, for example 40mm, and give the cell an alias through its properties. The documentation recommends referring to cells by the spreadsheet label and the alias, in the form <<MySheet>>.MyAlias, rather than Spreadsheet.B1; inside cells, an expression starts with an equal sign. Then bind the Pad length and the sketch dimensions to those aliases. Two documented precautions: editing a spreadsheet triggers a recompute of the model, and deleting referenced cells can break the model without warning.

The payoff comes when you reprint. After a fit test, you edit the cell, the model recalculates, and you export again without redrawing the part. Keep in mind that final accuracy also depends on the machine: the dimensional accuracy page covers the printer side of calibration.

Step 3: export to your slicer

The FreeCAD website states that the software exports to dozens of formats, including STEP, IGES, OBJ, and STL, in addition to its native FCStd format. The manual includes a chapter on preparing models for 3D printing, covering export to slicers and converting objects to meshes. Always save the FCStd file first: it is the one that keeps the sketch, constraints, and parameters. An export is only a frozen copy.

Two limitations deserve naming. First, versions: the FreeCAD manual was written for version 0.16. On October 20, 2026, the official repository marks 1.1.4, released September 28, as the latest stable release; the 1.1 branch launched in March 2026. The steps in this tutorial follow the Body, sketch, Pad, and spreadsheet flow as described in the FreeCAD documentation, whose repository was archived on April 1, 2026 and which names no target version; that flow was not replayed in an installation for this article. Second, compatibility: the Prusa knowledge base documents which formats PrusaSlicer accepts, not the export quality of every FreeCAD version. Always open the exported file in the slicer and inspect the mesh before starting a print.

The Prusa knowledge base also lists 3MF as the preferred format, used for project files, and notes that OBJ drops material and texture information on import. If your FreeCAD version offers 3MF export, confirm the slicer opens it correctly. The STL vs 3MF guide explains what each format carries. Once in PrusaSlicer or another slicer, check the scale: if the part shows up tiny or huge, check the units set in FreeCAD and the unit the slicer expects before looking for another cause.

Checks and limitations before you print

Before exporting, review the structure in the Model tab. One body, one sketch, one pad: if the tree contains unexpected items or error icons, read the Report view messages. Confirm the sketch is fully constrained and that the dimensions match what you measured on the original part.

One documented limitation concerns the spreadsheet: FreeCAD checks for cyclic dependencies, but by design that check stops at the level of the spreadsheet object. The documentation therefore advises against mixing, in one sheet, cells that drive the model and cells that read its results, such as a volume; use two sheets if you need both. Remember too that menu names, icons, and locations may differ in your installation: neither the manual written for 0.16 nor the online documentation used here states the exact interface version.

Finally, do not expect the first part to fit perfectly. Print a test, measure, adjust the relevant cell or constraint, export again. That loop is precisely what parametric modeling was built for. If you want to compare with a simpler modeling approach, the Tinkercad page describes that other tool.

Sources and limits

• FreeCAD : votre propre modeleur 3D paramétrique
• FreeCAD — manuel officiel (version0.16)
• Supported file formats
• FreeCAD documentation — Body
• FreeCAD documentation — Spreadsheet Workbench
• FreeCAD1.1.4 — official release

We organize manufacturer and community documentation; we have not measured these products ourselves. The manual for your exact model takes precedence over general guidance.