I just developed a new feature that I think will be useful for many
different design applications. I am calling it webbing (as in webbed-toes) and the general idea is that you have two circles of given diameters "d1" and "d2" on a plane. The first circle is centered at the origin, and the second circle is centered at the 2D point "c2". And you want to connect these circles as one object, using smooth continuous curves that neck down to minimum thickness "th" in between those circles. The way it forms this shape is by making a polygon out of circular arcs that alternate between convex and concave. The hard part is calculating the necessary radius r3 for the arcs that form the concave portion that will give the desired minimum thickness th. I spent some time working out the geometry equations involved, with some help from mathematics software to solve for r3, the final equation was pretty messy, but the results are worth it. Since it bulids on top of some of the base functions in my FunctionOpenSCAD library(mainly 'arc'), I decided to commit it to the same github project. https://github.com/thehans/FunctionalOpenSCAD/blob/master/webbing.scad The main function signature is function webbing(d1, d2, c2, th, r3) which will return a list of points for use with polygon. r3 is optional and is intended to override the r3 that would normally be calculated based on th. This is primarily because specifying a minimum thickness to neck down doesn't make sense for certain cases of overlapping circles where one is overlapped more than half. If a th is given that is larger than either d1 or d2 then it will be limited to the smallest diameter. The webbing function can be used to help model many kinda of shapes such as connecting rods, dumbbell like shapes, lever handles, parallel connected tubing, etc. Attached is an animated gif of the webbing_demo in webbing.scad, which shows the function being used with various combinations of parameters, and applied in a few different ways as examples. The leftmost shape in the animation is just to visualize the diameters and thickness that are being input to the webbing functions, with some different combinations of solid and hollow webbing shapes to the right. The other image is an example work-in-progress for a sort of motor cooling duct I'm designing. The flange is a union of a bunch of webbing between the various air holes and mounting bolt holes on the motor face. The webbing is only used for this flange feature of the model, as the other parts(not yet designed) will be tubular pipes sweeping around some curves. The end result is intended to resemble some types of automotive exhaust headers. Let me know what you think of this feature concept, or if you use it in any designs of your own! Hans _______________________________________________ OpenSCAD mailing list [hidden email] http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org |
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