18.3.1                    Parabolic reflector

To create parabolic reflector, we will use Create an arc of parabola tool - on the toolbar, we pick Sketcher −→ Sketcher geometries −→ Create an arc of parabola. This tool creates an arc of parabola by focus, vertex and endpoints.

We will create two arcs, with a spacing equal to the reflector thickness parameter (QW Vars.refl thick). The wire must be closed in order to obtain a solid by revolving the sketch.

Figure 1: Initial sketch - geometrical constraints were used so the wire is closed.

To parametrize the geometry of the model, we should use dimensional constraints - these are constraints associated with numeric data, for which you can use the expressions. The data will be taken from a QW Vars and Spreadsheet.

Figure 2: Clicking f(x) icon the Formula editor dialogue will appear and we can define the variable or formula that will be used.

Fully constrained sketch is shown below:

The orange color of datum constraint in edit mode means that it is expression dependent.

After finishing the sketch, we see in Solver messages that it is fully constrained (it has 0 degrees of freedom) - we pick Close and leave the sketch - which means we change the active workbench to QW-Modeller again. We can now rename the sketch.