topic Re: Loft along closed loop guide rails in Fusion Support Forum

Loft along closed loop guide rails

afgoody — Tue, 03 Jun 2025 17:10:24 GMT

Please reference the attached file. In the Loft feature (third from last in the timeline), you'll see I'm using four guide rails that all form a closed loop. I'm able to get what I need through subsequent mirror and combine operations, but don't understand why this is necessary. Shouldn't I be able to check Closed in the Loft options and then select all of the guide rail segments? Autodesk's Fusion guide says "To create a closed loop Loft, check Closed to connect the first and last profiles to each other."

When I try that, I get an error "Invalid rail geometry. Try using an open rail."

Re: Loft along closed loop guide rails

TheCADWhisperer — Tue, 03 Jun 2025 18:16:33 GMT

@afgoody

If you zoom in here - these curves do not line up.

Is this your true Design Intent?

Re: Loft along closed loop guide rails

afgoody — Tue, 03 Jun 2025 19:01:49 GMT

Yes, those are two separate sketches. I had to do it this way because Project (the function) projects normal to the target sketch plane with no apparent option to project normal to the source plane.

Re: Loft along closed loop guide rails

TheCADWhisperer — Tue, 03 Jun 2025 19:36:24 GMT

@afgoody

I would do an intersection curve projection instead. (This will be a bit tricky - I will have to make a demonstration model.)

On these Loft profiles, do you want these two top lines to be Horizontal, or do you want them to follow the angle of the angled plane?

For some reason the forum is really slow today.

Re: Loft along closed loop guide rails

afgoody — Tue, 03 Jun 2025 20:29:16 GMT

Sure, if we can address two issues in one, that'd be great. But, I think my original issue will persist regardless of the exact geometry of the rails, as long as they still intersect the profiles of course. I think the top of those profiles needs to stay horizontal, but it's hard to tell exactly. I won't know for sure if I got it right until I run some test prints. Here are some pictures of the actual product. I know some of my dimensions are off, but I'm away from home right now so I'm just working on the method more than the exact design at this point.

Re: Loft along closed loop guide rails

davebYYPCU — Wed, 04 Jun 2025 03:58:02 GMT

Like this?

The Lens is not going under at the moment.

Might help...

Re: Loft along closed loop guide rails

afgoody — Wed, 04 Jun 2025 15:07:22 GMT

@davebYYPCU Thank you. I see how you used sketch lines to create surface tools to be used back in the solid workspace and you segmented the higher profile sketch to break down the more complicated geometries into smaller "challenges." Lessons learned.

What are the construction lines you added here?

While this proved to be the better approach - one in which a closed loop loft would not have resulted in the proper geometry (at least not without more profiles along the path) - I'd still like to understand the answer to my original question...Shouldn't I be able to check Closed in the Loft options and then select all of the guide rail segments?

Re: Loft along closed loop guide rails

davebYYPCU — Wed, 04 Jun 2025 15:37:22 GMT

Construction lines are points for the Hole Tool.

Opinion : Closed Loft - would work if you have more than 2 profiles, (did you select the loop of 3 profiles?) otherwise the Loft without rails, would be a straight 180 deg line, and has no details how to get past that proposal. At the same time, the rails at the profiles, are crossing the profile in both directions. In short - not enough construction articles for that request.

Might help…

Re: Loft along closed loop guide rails

afgoody — Wed, 04 Jun 2025 16:39:50 GMT

Ah, missed that (point for the hole tool). I'll need to measure those if I end up even needing them for my actual intended project. But, again, thanks for the head start!

OK, I created a simpler file (attached) to try and demonstrate what I think you're saying is a limitation of the Loft command on a closed loop.

Using that saved state (three profiles and a guide rail) as a starting point, checking or unchecking Loft: Closed does not change anything:

But, if I remove the rail, it does affect the result:

CLOSED DESELECTED

CLOSED SELECTED

But, the use case I originally asked about was having only two profiles w/ at least one guide rail. In this case, it seems to me that Loft should be able to use the guide rail to achieve something other than lofting along a 180° line (which of course would be the case without any guide rails). As we saw in the original file, it can do this, but seemingly not when the rail is closed.

I think I understand this limitation now and can work around it, but still think Fusion could add this to the Loft command.