topic Remixing an STL and Loft Tool error: "Would flow in an invalid direction"? in Fusion Design, Validate & Document Forum

Remixing an STL and Loft Tool error: "Would flow in an invalid direction"?

mallerya — Wed, 22 Jul 2020 12:28:43 GMT

Hello! 🙂

Project description:
I'm remixing a fan attachment for my 3D printer from an STL file. The overall goal was to simply shift the fan on attachment fitting from the center point location to instead be positioned at the top perimeter's side of the adapter. The final result should have the top perimeter side of the fan at a 90 degree angle to the C-shaped fitting, thus dropping the fan by a few millimetres and allowing better clearance for other components on the print-head.

The problem:
I projected the side of the model of where the fan fits to a new sketch and I did this with the other side where the fitting attaches to the heat spreader separately. After extruding the fitting's length to match the original model's specifications, I performed a point-to-point move and shifted it toward the top perimeter of the fan-facing side. Now, I am trying to loft the remaining faces from fan facing side alongside the fitting, but then I run into the following error:

"Warning: The loft would flow in an invalid direction.
Try adjusting the continuity settings. If two adjacent profiles are on the same plane, try moving one of these."

I am not sure how to begin fixing this issue. Googling did not get me very far. In my experience, solving problems in Fusion 360 is a bit tricky since the errors are all different on a case-by-case basis.

Sometimes when using the project tool in Fusion, I notice that some of the points may not line up super accurately. I tried merging some of the faces of the C-shaped body since this has fixed some things in the past for me. However, this did solve the issue.

Why is this happening and how do I solve it? Images and videos are highly appreciated 😄 (visual learner here)

Re: Remixing an STL and Loft Tool error: "Would flow in an invalid direction"?

TrippyLighting — Wed, 22 Jul 2020 12:12:47 GMT

@mallerya wrote:

I am not sure how to begin fixing this issue.

I am.

Use the .stl file strictly as a visual reference and create the design from scratch using Fusion 360's native solid modeling or surface (or T-Spline ) tools.

.stl files contain triangulated meshes, the least common denominator of 3D geometry. Finite resolution without topology.

CAD software, on the other hand, works with BRep and NURBS geometry. Mathematically precise, resolution free surfaces. When those are converted into .stl a substantial and essential amount of information is lost and cannot be 100% re-created.

Re: Remixing an STL and Loft Tool error: "Would flow in an invalid direction"?

TheCADWhisperer — Wed, 22 Jul 2020 12:38:34 GMT

@mallerya wrote:
I am not sure how to begin fixing this issue.

The geometry for this one is so simple, yet interesting enough that it will make an excellent example for learning how to use Fusion 360.

Have you created any previous projects in Fusion?

Step 1.

Start a new file.

Step 2.

Create the sketch shown on the XY plane.

Re: Remixing an STL and Loft Tool error: "Would flow in an invalid direction"?

mallerya — Wed, 22 Jul 2020 12:40:40 GMT

Right, I understand the issues of an STL file in general. But this is why I simply tried projecting the model's geometry to a sketch and began working from there. I am skeptical that starting completely from scratch would just solve the issue, as I also attempted merging many of the triangular faces which should repair many of the triangles that could cause a potential issue with lofting (from what I understand).

Re: Remixing an STL and Loft Tool error: "Would flow in an invalid direction"?

TheCADWhisperer — Wed, 22 Jul 2020 12:50:45 GMT

@mallerya wrote:
I am skeptical that starting completely from scratch would just solve the issue...

OK.

Re: Remixing an STL and Loft Tool error: "Would flow in an invalid direction"?

TrippyLighting — Wed, 22 Jul 2020 20:55:31 GMT

@mallerya wrote:

Right, I understand the issues of an STL file in general. But this is why I simply tried projecting the model's geometry to a sketch and began working from there. I am skeptical that starting completely from scratch would just solve the issue, as I also attempted merging many of the triangular faces which should repair many of the triangles that could cause a potential issue with lofting (from what I understand).

You clearly don't understand the implications of trying to use a triangulated mesh file and your skepticism is unwarranted.

The two other dudes in this thread have a combined 70 years of professional experience in CAD. @TheCADWhisperer teaches it at the college level.

Re: Remixing an STL and Loft Tool error: "Would flow in an invalid direction"?

mallerya — Thu, 23 Jul 2020 00:30:28 GMT

Pardon my ignorance...

I was never doubting their experience. Their solution was just not the one I was hoping for.

What if there comes a time where I need to remix another model but with much more complicated geometry? There has to be a way how to do it without completely reconstructing it...! 🤔

I attempted to repair the faces so that there are much less joints/triangles (see pic below), but lofting will not cooperate. Merging faces has fixed this issues in the past for me on other remixes. Otherwise, I would have to shave off a little bit of the object and extrude them out again to repair it...

Maybe guide rails would help the lofting a bit better work? I am open to suggestions but I would rather not have to remake it from scratch. It would be more time expensive than to remix the existing model.... The inside air duct shape of the fan would be easy, but the outer "bowl" shape, the shape & distance of the clamp fitting, and the distance of the holes/threads for the fan would all take a lot of time to figure out/recreate (for me at least).

Re: Remixing an STL and Loft Tool error: "Would flow in an invalid direction"?

mallerya — Thu, 23 Jul 2020 01:00:49 GMT

Okay! So while writing my last reply and glancing at the screenshot included, I think I saw a relationship issue between the two faces I was trying to loft from.

Correct me if I am wrong, but the highlighted yellow sections are the "problematic" parts that fusion is trying to inform me as to why the loft will not work. When looking at the points that are attached, there was a lot of them being cast from the rounded cornering section of the sketches face. These were also trying to connected to the bottom section of the C-shaped fitting which, just by looking at the vector between the two points, did not seem right. That is when I remembered that I used a project-to-sketch for this face, and the rounded corners I had mentioned earlier did not create a smooth round corner. Instead, it consisted of many small points to emulate a "rounding" shape. So the body of the model in this particular case, may not have been the problem. It could have been the sketch's face instead...

All I needed to do to fix this was to create a new sketch on top of the projected one, stencil out the straight lines from the projected sketch, then use a tangent arc to round the corners (see below).

And before performing the loft, I also undid the face-merging I did previously, because it was causing some minor artifacts in the rounding shape of the object.

And the result.....

Ta-Da! This was all I needed to proceed forward in my remix. I understand that I am not the most well-versed with Fusion 360, but hopefully this solution will prove useful to someone else searching for an answer. It's a shame I couldn't get a suggestion like this sooner, but I thank all the Fusion360 veterans that replied for encouraging me to learn new things anyways despite it going against the attempted workflow.

Re: Remixing an STL and Loft Tool error: "Would flow in an invalid direction"?

TrippyLighting — Thu, 23 Jul 2020 09:51:03 GMT

@mallerya wrote:

It's a shame I couldn't get a suggestion like this sooner, but I thank all the Fusion360 veterans that replied for encouraging me to learn new things anyways despite it going against the attempted workflow.

I would not consider that a shame. A bad workflow even when seemingly successful is still a bad workflow. Obviously our encouragement went absolutely nowhere!