QCAD is not a parametric 3D CAD program. You have to know what your part will look like before you draw it, because all it really does is neatly draw lines and curves.
Contrast with Solvespace (or FreeCAD, or any of the popular commercial parametric 3D CAD programs), which lets you specify relationships (constraints) between elements in 2D and 3D. The shape of your part is the finished result, not the starting point.
Contrast with Solvespace (or FreeCAD, or any of the popular commercial parametric 3D CAD programs), which lets you specify relationships (constraints) between elements in 2D and 3D. The shape of your part is the finished result, not the starting point.