Hans-Werner nous apporta ses lumieres ainsi en ce 2004-09-24 18:27... :


>I head the idea to construct a screw and the opposite part; a nut ? (Sorry,

>For this I had the idea to contruct a flat polygon (6 corners), cut off a
>circle inside, sweep it to the third dimension and then use CSG to do the
>remaining.
>But how to cut off the circle inside the polygon ?
>So, the first step is to define the polygon.
>
># declare Radius_Aussen = 0.5;
># declare Radius_Innen  = 0.3;
># declare Anfangswinkel = 0.0;
># declare Mittelpunkt   = <0.0, 0.0, 0.0>;
># declare Winkel = Anfangswinkel;
># declare Increment = pi/3.0;
># declare X_Koordinate  = 0.0;
># declare Y_Koordinate  = 0.0;
># declare Eckpunkt      = array [6];
># declare Index         = 0;
>
>
># while (Index < 6)
>  # X_Koordinate = Mittelpunkt.x + Radius_Aussen * Winkel; // This does not
>work
>  # Y_Koordinate = Mittelpunkt.y + Radius_Aussen * Winkel; // This does not
>work
>  # Eckpunkt [Index] = <X_Koordinate, Y_Koordinate>;
>  # Index = Index + 1;
>  # Winkel = Anfangswinkel + Index * Increment;
># end
># declare Grundflaeche =
>polygon
>{
>  6, Eckpunkt[0], Eckpunkt[1], Eckpunkt[2],
>     Eckpunkt[3], Eckpunkt[4], Eckpunkt[5]
>}
>
>Thank you
>
>
>  
>
Planes are objects that can be intersected (intersection{}) or 
diferenced (difference{}), they do have a deffinite interior and exterior.
In your case, you can start with a cylinder or a sphere, use 6 planes to 
chop off the faces and a cylinder to bore the hole.
You can also start with a prism from whitch you subtract a cylinder.

Alain

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