Issue with loft rail

[jphalip]

Hi,

I'm trying to create a loft between two profiles (a circle and a rectangle with rounded corners) using a spline centerline. My issue is that, even though I've selected a centerline, it still creates another rail on the side. And unfortunately I can't seem to move that rail to when I'd like.

Here's the issue:

I tried to edit the loft and drag the rail's position:

But then after clicking 'Ok', the rail returns to the wrong position:

How can I fix this? Please see the problematic Fusion 360 file attached.

Thanks in advance!

Julien

[wersy]

I just found out, it makes a difference depending on where you place the seam.

[jphalip]

Thank you all for the thoughtful replies.

I recreated the whole design from scratch and constrained all the sketches (except the splines one). Hopefully that resolves any potential misalignments between the sketches themselves. I also tried creating the centerline with arcs instead of a spline, as suggested by @TheCADWhisperer. See the new file attached.

However, even with all of that, the resulting loft still isn't symmetrical... How strange!

Let me know if you can think of a way to make this work. Otherwise I'll try some of the workarounds that have been suggested earlier in this thread.

[jphalip]

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@wersy wrote:

I just found out, it makes a difference depending on where you place the seam.

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Yes, that's what I had found too, which is why I was asking about how to fix the seam in my original post. My guess is that Fusion 360 takes two points (source and destination) randomly as a guide for the extrapolation. And the fact that the rectangle has rounded corners makes it pick the wrong points. That's fine as a default behavior, but what puzzles me is why it won't save the new point after you drag it and click 'Ok'.

[HughesTooling · Accepted solution]

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@jphalip wrote:

Thank you all for the thoughtful replies.

However, even with all of that, the resulting loft still isn't symmetrical... How strange!

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Did you see my post about spitting the circles in half so you can pick a seam at any quadrant?

Actually seems to work well in the middle of one of the long edges. See attached file,

[jphalip]

Very interesting. I confirm that this works, thank you!

By the way, how did you split the circles? By deleting the circles and recreating them using 4 arcs?

Using your method, the seem is correctly centered by default, which is great.

However, one thing I still don't quite understand. Why isn't it possible to move the seam and then save the new seam? If Fusion 360 properly saved the change, I think the original sketch would have worked too.

[HughesTooling]

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@jphalip wrote:

Very interesting. I confirm that this works, thank you!

By the way, how did you split the circles? By deleting the circles and recreating them using 4 arcs?

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@jphalip All I did was extend the construction line you had then used break from the modify menu. Also note the Extend option on the same menu.

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@jphalip wrote:

However, one thing I still don't quite understand. Why isn't it possible to move the seam and then save the new seam? If Fusion 360 properly saved the change, I think the original sketch would have worked too.

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I think the solid version of loft is just finding the simplest answer, with the surface version you have more control. There are a few situations where the surface tools give better results.

[daniel_gladyshev]

spliting the circle is a hack, but the real problem is how to move the line on the surface, or better simple get rid of it.
i have a similar situation, and it driving me nuts why the surface created by loft on a round object has a line on it.

loft from circle to slot form so they are perfect curves

[TrippyLighting]

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@daniel_gladyshev wrote:

spliting the circle is a hack,

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No, it isn't

You are also using the wrong loft setting if you are only getting 1 edge.

If you enable the Keep tangent edges, then you'll get 4 edges with tangent surface transitions and better surfaces.

Then spitting the circle will provide you with better control over the shape.