OpenSCAD revolve: powerful and fast module for screws and more

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This library has been made obsolete by Revolve2 ------------------------ Introducing Revolve ================ This OpenSCAD module enables rotational extrusion of generic user-defined profiles, introducing a pitch along the longitudinal axis, the most common application being the creation of screws. The solid is built as a single polyhedron by transforming the 2D points found in the profile array. No boolean operation is necessary, aiming at achieving the ultimate performance by producing the simplest possible object for the desired level of detail. --- # Arguments `revolve( profile, length, nthreads, f);` * *profile:* array of 2D points defined as [[z1, f(z1)], [z2, f(z2)], ... [zn,f(zn)]]. The function f(z) describes the shape of the thread (trapezoidal, square, triangular, sinusoidal, ...). The shape of the profile can be refined by adding more points, however this will also make it heavier to handle. The profile should be defined over a closed interval (including the extremes) representing one period of the thread. The linspace helper function might be used to create the profile from a mathematical function (see example below). * *length:* how far to go in the longitudinal direction, note that the mesh size increases linearly with this parameter. * *nthreads:* allows the creation of multiple threads, it should be an integer. Negative numbers are also accepted, generating left threads. Zero results in no pitch, similar to rotate_extrude. * *f:* the number of subdivisions in the angular direction, similar to $fn for a cylinder. Note that if this parameter is too small, the resulting mesh could be completely wrong. A sufficient condition to satisfy correctness is: f>period*nthreads/dz; where dz is the minimum z increment defined in the profile In the longitudinal direction the number of subdivisions is controlled directly by the number of points in the profile. --- # Example ```openscad use <revolve.scad> period = 6; // choose the pitch length = 30; // the tallness nthreads = 7; // the number of threads (<0 for left threads) f = undef; // angular finesse, undef for autocompute // A sinusoidal profile function... function prof_sin(z) = [z, 10+sin(z*360/period)]; // ...which becomes a profile array with the help of linspace prof = [for (z=linspace(start=0, stop=period, n=16)) prof_sin(z)]; // now the screw render(convexity=10) revolve( prof, length=length, nthreads=nthreads, f=f); ``` --- A limited set of the module capabilities can be previewed in the Customizer.