Hi Kreten. Rhino 3 will develop the 45 degree miters by sweeping a single profile curve along these rails. In R4, a 2-rail sweep will produce the frame as a single creased surface (point editable). It's not necessary to rotate profile curves 45 degrees to make the mitered joints in Rhino. So not sure where Amapi has any advantage... Or maybe you just meant to say not necessary to align the profile curve perpendicular to the rail curve (90 degrees)?... I prefer to draw the profile curve in place on the rail curve (perpendicular to the curve). It helps me visualize exactly the proportion of the two curves. Drawing a flat profile which will be swept in a vertical position along a rail which is away from my drawing space feels very disconnected to me. So i hope to see c-plane orientation tools in Moi soon...

jonah