SolveSpace

What SolveSpace is

SolveSpace is a parametric computer-aided design program built on a constraint solver. Instead of drawing fixed geometry, you describe relationships: this line is horizontal, these two edges are equal, this point sits at the midpoint of that one, this angle is thirty degrees. The solver then finds the shape that satisfies all of them, and every later change propagates through the model. The whole application is a single small executable with no installer and no runtime dependencies, which makes it unusually portable for a CAD tool, and it manages a full parametric history, three-dimensional booleans, assemblies with moving parts and export to both mesh and STEP formats.

How a modelling workflow runs

Modelling starts on a workplane. You draw lines, rectangles, circles and arcs, then constrain them until the sketch is fully determined; the program changes the colour of the sketch when every degree of freedom has been resolved, which is the signal that the geometry is stable enough to build on. Dimensions are added as constraints, either as numbers you type or as expressions that reference other dimensions, so a part can be driven by a handful of controlling values. Groups then stack: a group can extrude a sketch into a solid, revolve it around an axis, create a helical thread, or perform a boolean union, difference or intersection with another solid. Each group keeps its own history, and suppressing or editing an earlier group propagates through everything below it.

Because the same solver works in three dimensions, SolveSpace is also a mechanism simulator. A new group in assembly mode links a copy of a part and constrains it against the rest of the model, and the resulting degrees of freedom can be dragged interactively to see how the linkage moves. That makes it practical to check whether a four-bar linkage locks up, whether a hinge swings clear, or whether a slider reaches the end of its travel, all before any material is cut. Output options cover the range most small workshops need: STL and other mesh formats for printing, STEP for exchanging real solid geometry with industrial CAD, and DXF, SVG or PDF of projected views for laser cutting and technical documentation.

Practical settings and limits

The trade-off for the small footprint is a narrow feature set. There are no fillets or chamfers as operations, no sheet metal tools, no surface modelling beyond swept, revolved and extruded shapes, no drawing sheets with dimensions and annotation, and no assembly bill of materials. The interface is idiosyncratic, mouse-driven with a sparse toolbar, and newcomers often spend the first hour learning where the constraint buttons live. Models with hundreds of features become slow to rebuild, and the solver can fail to converge on over-constrained sketches, in which case the offending constraint must be found and removed. Sketch import is limited compared with commercial software, so importing a complex STEP assembly and editing it feature by feature is not realistic.

Who should choose something else

If you need production drawings with tolerances, large assemblies or surface modelling, a full parametric CAD package is the honest answer, even if it costs money. If your work is mesh sculpting rather than engineering geometry, a polygon modeller fits better. If you would rather describe parts as code, a script-based solid modeller is faster for parametric families. SolveSpace earns its place for small mechanical parts, linkages and quick parametric experiments that need real solids and STEP output without a licence fee.