Morph circle to oval in openscad

Question

I am trying to create a fan duct in openscad, flattening the duct from circular to oval. Is there a way to do this in openscad? If not, is there any other programmatic way to generate this type of 3d model?

Thanks Dennis

Answer 1

Assuming by 'oval' you mean elipse, then the following creates a solid tapering from a circle to an ellipse:

    Delta=0.01;

    module connector (height,radius,eccentricity) {
        hull() {
          linear_extrude(height=Delta)
             circle(r=radius);
          translate([0,0,height - Delta])   
             linear_extrude(height=Delta) 
                scale([1,eccentricity]) 
                   circle(r=radius);
        }
      }

      connector(20,6,0.6);

You could make the tube by subtracting a smaller version:

module tube(height, radius, eccentricity=1, thickness) {
     difference() {
       connector(height,radius,eccentricity);
       translate([0,0,-(Delta+thickness)]) 
         connector(height + 2* (Delta +thickness) ,radius-thickness, eccentricity);
     }
   }
   tube(20,8,0.6,2);

but the wall thickness will not be uniform. To make a uniform wall, use minkowski to add the wall:

module tube(height, radius, eccentricity=1, thickness) {
    difference() {
      minkowski() {
        connector(height,radius,eccentricity);
        cylinder(height=height,r=thickness);
      }
    translate([0,0,-(Delta+thickness)]) 
        connector(height + 2* (Delta +thickness) ,radius, eccentricity);
    }
  }

tube(20,8,0.6,2);