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Maintaining design intent with Lofts?

Question asked by Stephen Stickel on Dec 21, 2016
Latest reply on Jan 12, 2017 by Stephen Stickel

I'm in trouble. I had some parts modeled for machining, but recently was convinced to redesign them for investment casting. This means that I've run out of skills and need help.

 

I have already added sketch pictures (in 2 axis) to my part to help me determine its contours. I have set up multiple planes along an outer curve, onto which I intend to sketch Profiles (cross sections) so that I can use the Lofted Base feature. Now, I'm stuck.

 

I have no way to know what shape (height and width) to sketch onto each plane. In other words, I don't know the 'envelope' that each Profile has to fit into. I have no reference. Every Loft tutorial I can find makes it look easy... because they're free-forming it, they're not trying to match a predetermined shape. My desired shape transforms from horizontal rectangle to vertical rectangle to almost-quarter-ellipse as it moves through 3 curves.

 

I can make a basic solid shape that defines the 'envelope', but when I used that part as a guide for my Profiles, i ran into big problems with Parent/Child. I used section views of the solid shape to show me my 'envelopes', and that worked great; I just sketched the refined shape within each 'envelope'. When I was done, my desired form was buried inside the solid shape, unfortunately. Suppressing or deleting the solid shape (parent) wrecked everything else. I'm using 2006, BTW.

 

I tried making 3D curves that defined the form (edges)of the desired part, hoping that I would be able to snap to them where they passed through each new plane, again in hopes of defining the 'envelope'. Nope, they won't snap, and trying to create relations between the 3D curve and my sketched lines is a nightmare.

 

Any ideas on how to accurately replicate complex forms using lofts? Any help would be greatly appreciated. Thanks.

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