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Loft tool help- design strategy for complex shape

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I am attempting to model an injection molded instrument case that has a quite complex shape- essentially two cylindrical tubes (for batteries) blended into an upper section that is an elongated curved (submarine hull) shape. It needs to hold an LCD, circuit board, and batteries and be as small as possible given the components. There is a cap on one end and a threaded fitting on the other.

I'm using VW 10.1 Mechanical, Mac OSX 10.2.6, G4/ 500/ 1G ram.

My strategy was to

1) Place the components that I need to house in a 3D drawing

2) Draw smooth polyline contours in 2D to determine clearances and general shape

3) Use this shape to determine the boundaries of my cross sections

4) Draw a polyline cross section at the largest diameter

5) Duplicate this polyline and edit the (bezier) vertexes to describe several other cross sections

6) Convert the polyline cross sections to NURBS, and place the NURBS cross sections in 3D space where they belong.

7) Use the loft tool to create the shape.

8) Shell the solid

9) Section the solid to create two halves and an opening for a clear screen.

10) Add separately drawn interior details, supports, ends, etc with the add solids command.

Right now I am breaking down with the Loft tool. If I loft only the three cross sections that are very close in size and shape, a smooth shape is created. If I add another cross section- one where the shape changes, the loft yields a twisted or creased and unfair shape, and I can't seem to untwist it. The object is symmetrical, like a boat hull. The NURBS curves have exactly the same number of vertexes and are all variants of the same basic shape. I try to specify the alignment in the loft creation dialog so the points on the guide line line up- say along the top centerline, where they should be exactly in a straight line. But adjusting in 1 degree increments does not give me the ability to line them up exactly, and the lofted shape appears to have some "wrinkles" in it. I've tried to attach an image that shows how the lines don't quite line up.

I feel there must be something I am not understanding about how to use the Loft tool- or perhaps my strategy is not the best? Would another tool or approach such as creating surface from curves be more appropriate, or would it be better to loft the shape in sections and then combine them? I would appreciate any comments about the overall strategy, as well as any insight into the loft tool and aligning points.


RonR -

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