The directrix should simultaneously translate n units in parallel to the y-axes, so its equation is l: y = n - 1/4a.
Using the above considerations, the focus and directrix are described in Figure 4.
2], we managed to find a focus and a directrix that do not depend on the selection of points on [[lambda].
The constructive parameters of the workpiece and tool and also the generation ones determine the form of the directrix
and generatrix of the polygonal processed surface.
When students have found the points that are twice as far from the focus as they are from the directrix
(r = 2 l) they can join them to form an hyperbola with eccentricity e = 2.
Use [constructions] parallel to find another point, P', which is the same distance from the directrix and from the focus.
Choose the pointer and use it to move the point A up and down the directrix.
Thus P is on the locus of points equidistant from the directrix plane through D and the focus point F.
Practically, at the generation of the complex real surfaces the curve C as circular helix is generated as directrix D of the surface.
The most extended application of this case of simple movements composition is represented the generation of the directrix D at the generation of the main extended complex surfaces in techniques, the helical cylindrical surfaces with all kind of profiles.
The aspects shown in this paper represent original contribution concerning the cinematic generation of the circular helix used as directrix D at the generation of real complex surfaces of the type cylindrical helical surfaces.