Lofting of hollow features

[Anonymous]

Hi all, 

I'm new to Fusion 360 (and learning CAD bit-by-bit in general); picked up a copy today through the Autodesk student program. 

What I'm attempting to figure out is something that I've never learned completely to my satisfaction - lofting of features that include hollows.

The screenshot explains this fairly well - lofting from start to finish a cylindrical structure that has hollow structures in between the concentric circles. To make the illustration easy, the two rings are 5mm and the angles and numbers of arcs are consistent between. The behavior of the lofting tools frustrates me (it also did in SolidWorks, to which I am more accustomed) - the extrusion tools obey hollows and will extrude a sketch correctly, but the lofts do not.

What is the "best practices" method for dealing with scenarios like this, especially in scenarios where the guides are not linear and the final product is expected to have axial symmetry?

(if the screenshot gives it away, I am an aerospace engineering student)

Best regards,

E.F.

[jeff_strater]

Hi @Anonymous,

Yes, this is a known limitation of Loft.  There are a couple of approaches that can work:

1. Two separate solid lofts.  This is what most people will do.  Loft the outer profile as a solid, then loft the inner profile as a subtract operation
2. Use surface loft.  Loft the inside and outside surfaces separately, then patch the ends and stitch it all back together.  
3. Or, if it is a constant thickness, just loft one side and Thicken it in the other direction.

I can make a screencast, if that will help.

Jeff

[Anonymous]

Hi @jeff_strater,

What I've thought about doing in the past is performing a rotational extrusion of the main body, lofting the internal cavity, and then using the circular pattern tools to establish the correct number of instances.

I'd love to see a screencast to see how you would approach the problem.

Thank you,

efedele 

[jeff_strater · Accepted solution]

I tried a number of approaches, but the one that got me the closest was not to use Loft at all.  As you suggested:  Use Revolve for the shape (I started with Loft, but it needs a lot of rails to get the shape I think you are after), then use Sweep for the "holes", and using a Silhouette edge project for the path.  I had to extend the path a bit to get the holes to punch through the other side.

Here is a screencast of a walkthrough of the design (I'd already created it).  There are a few kludges in it, but I think it gets close.  Model attached.

That's the best I can do for a Friday night...

Jeff