Loft, change form while maintaining proportions

[melfio]

I'll try to explain myself briefly:

I'd like to loft between these three sketches (see image), I want to follow the curvature set by the curves joining the bottom corners and the curve joining the top angles. The thing is I want the whole shape to follow this convex curvature in a proportionate way. As of now, the two rounded corners takes a "shortcut", creating a more narrow convex curve, and results in a slanted edge.

I've tried creating "Plane at Angle" and drawing a curve there, joining the curved ("top") corners of the two closest sketches, but that seems to be too many rails for the Loft tool to handle.

It is important that the bottom of the body follows the path set by the two curves on the XZ-plane and that the sides are vertical (up to the fillet). Otherwise I'd just use "Create Form" tool and get the requested curvature of the top side, unfortunately I dont know how to make Create Form follow the shape of a sketch precicely, definitely not on both the XZ and YZ axis. But maybe that is a better path to take?

[jeff_strater]

the main tools in Loft for changing the shape are:

1. adding more sections.  This can help in some cases, or actually make the problem worse, because Loft does go exactly through those sections.
2. using centerline rails.  The difference between a centerline rail and a "regular" rail is centerline is really more of a guideline than an actual constraint.  From your description, this sounds it may help you get the shape you are looking for
3. Adding more "regular" rails.  This is probably the most fine-grained control that we have in Loft.  You can really control the shape by adding more rails.  There should be no limit to the number of non-centerline rails allowed in Loft.  However, rails tend to be a bit harder to use.  You have to make certain that the rail intersects the profile exactly.  This usually requires you to use the Project command (or Project Intersect) in sketch to create points that are exactly constrained to be on the profile.

Hope this helps to explain the range of possibilities for complex shapes in loft.  There is sometimes a bit of trial-and-error to get it to exactly the shape you want.  And, sometimes, depending on your requirements, using a Sculpt body is the best way to get a more-complex (but less-precise) shape.

Jeff Strater (Fusion development)

[Anonymous]

my Keyboard is bad, but also look into two rail sweep, which scales based on spacing between rails.  I used this in example here

http://forums.autodesk.com/t5/design-and-documentation/fillet-rounded-corners-issue/td-p/5739569/pag...

Jesse

[melfio]

Brilliant, thank you both, jeff.strater and jjurban55. Now for the next problem in my work flow.. But I'll post another thread for that issue. 🙂

[gautham_kattethota]

Hi,

To get better control over the shape of the loft near the rounded corners, it would be better if you could add one or more rails on each side of your apparently symmetrical profiles.  This will add more shape contraints for the loft.  There is no limit to the number of rails that can be defined for a loft.

You dont need to add a Plane at an Angle.  You could rather create a "Plane through three Points", by selecting a point on each of the three profiles. Then project those points on to the sketch defined on that plane and use them to define the rails.  

Hope this helps.  If not please post your file and we can take a closer look.

Regards

Gautham (Autodesk)