Shell a body or Thicken a surface

[mr.rickwright]

Ok experts I think I need help!
I have tried, read, tried again and can't seem to figure out what I am doing wrong (maybe a sliver I'm not seeing).

Objective:   create a kayak driven by a few user parameters 

Status:  created the base sketches needed for lofting a surface of the kayak and got the loft to successfully follow the rails from one pointy end to the other over the 4 profiles.

Problem 1:  Unable to thicken the surface outward (or in any direction) by the desired 0.1875".  Fusion just bombs when I try.

Problem 2:  Since I couldn't get thicken to work on the surface I successfully used boundary fill to create a body inside the surface, thinking I could shell out the inside leaving a 0.1875" wall.   

No such luck. That Bombs out too.

If anyone can advise what I'm doing wrong or a better way to approach this I would be very appreciative.

Copy of component is attached below.

Thanks 

Rick W

[Johnc911 · Accepted solution]

Looking at your sketches. Do you see how your boat comes to an infinitely thin point at both ends? This isn't a geometry that the CAD kernel is able thicken or shell. Try to make a more real-world profile at the ends and then you should have no problem thickening or shelling the geometry. This will be achieved by changing your rails to give some thickness at the bow and stern. Also check your main keel curve it seems to have some very aggressive curvature at the ends, use the curvature combs to make your curves smoother.

[TrippyLighting · Accepted solution]

Lofting creates NURBS surfaces. The shape of NURBS surfaces is controlled by a quadrilateral mesh of control points with (mathematical ) weighs.

When lofting into a single point the weights in these control vertices approach infinity. The software can then either

1. Crash

2. Refuse to complete the operation

3. Approximate

Fusion 360 approximates, but the result is that the curvature of the surface approaching that curvature gets increasingly worse and that is the reason you cannot thicken these surfaces. Lofting such surfaces is really and advanced topic 😉 

The image hopefully shows how these control points all seem to flow toward the tip of the loft.

[mr.rickwright]

[...]Lofting such surfaces is really and advanced topic.

Peter; thanks I love how you explain the why behind the answer. Once I take the points off I have no problem with the thicken command.   I will work on adding some Thickness to the point.   In wood working we are always seeking an infinitely sharp point on our blades so we can make infinitely thin shavings but in reality the best is about 5 microns   In my reality it's about two thou'.

I assume the Shell command has the same problem on the body that was formed from the lofted surface.

Thanks again.

Rick W

[mr.rickwright]

John;

Thanks for taking a look.    I tried lofting without the points and the thicken worked fine, I will work on providing some thickness to the pointy ends so that I don't have the infinity asymptote. 

As to the keel sketch the design intent is to have a sharp curvature at the fore foot so I will explore alternative ways to develop it with perhaps a CV spline or an arc.

As to the shell failure, I assume it is the same infinity problem.

Thanks again for the quick and "to-the-point" response! 

Rick W