Attempting to do a curved ramp to a curved (non planar) end profile

[eSonOfAnder]

I feel like I must be missing something simple here, because I feel like this shouldn't be this difficult. I am attempting to create an incline that runs along a curved shape, but the thing that none of the solutions I've found online doesn't address is that the endpoint of the incline in my scenario is a curve, not a straight line / plane, which means I cannot just do a loft from one to the other.

This article suggests that you should be able to select an edge or vertex to use as a loft profile??? I've never been able to do that here, and suspect that if I could, that would address my needs, as I'd be able to just select the starting segment and end segment arc as the loft profiles, and then use the curves as guide rails.

I'm sorry if the answer is obvious, but I really am just not seeing it. I thought that maybe I could just use two sketches and loft between them, one that includes the curved segment and the circle on the right side at the base, and the second sketch that just includes the circle at the height where I want it to end, but that produces some bizarre results that I didn't see any way of cleaning up to be what I wanted, because pretty much nothing here is planar. (The results of using these as profiles for a loft are also inconsistent - sometimes it gives me a strange stretched out shape, sometimes it literally does nothing after performing the exact same steps.)

Base profileat base heightLoft profileat loft height

If anybody has any suggestions, please let me know! It really seems like the issue is that I'm trying to end at the circle/cylinder rather than a straight planar surface, and I just can't figure out how to deal with it.

[jhackney1972]

Please attach your model. 

If you do not know how to attach your Fusion 360 model follow these easy steps. Open the model in Fusion 360, select the File menu, then Export and save as a F3D or F3Z file to your hard drive. Then use the Attachments section, of a forum post, to attach it.

[eSonOfAnder]

Attached is a simplified model with just the component involved in the question posted. (The original design is for a commercial product that I am designing, so not really something I am comfortable attaching to a public forum post.)

[davebYYPCU]

You haven’t said, how the incline has to transition at each end of this rib.

Is the top face to be tangent to the lower rib, tangent to top circular face?  

Just this one, or to the mirrored one on the left as well?  

Will it be part of a pattern?

[jhackney1972]

I am not sure the model you attached is representative of what you need.  You original screen capture shows a sloped path.  Anyway, on the model you supplied, I think this is a Sweep and not a Loft.  Model is attached.

[davebYYPCU · Accepted solution]

I must be missing something simple here,

You can Loft from model faces, too.

Might help...

[eSonOfAnder]

Yes, this is exactly the result that I was describing. The primary missing piece for me was the 0mm surface offset and extension at the intersection of the curved segment and the cylinder. I knew there had to be a pretty simple way of accomplishing this. Thank you.

[eSonOfAnder]

Take a look at davebYYPCU's second reply: https://forums.autodesk.com/t5/fusion-design-validate-document/attempting-to-do-a-curved-ramp-to-a-c...

[eSonOfAnder]

Sadly that only works for the shorter segment. Attempting to do the same thing around the outer, longer segment produces... interesting results.

Oh well, I opened a ticket with support to see if they can give any guidance on how to get the tools to act as expected. Thanks anyway.

[davebYYPCU]

Yeah, Loft is not as stable as other tools, has a tendency to shrink wrap, but not seen weird like that.

needs more geometry to control it.

All is not lost, 

use one original curve as the Rail, and one connected edge of the surface face, 

Surface Loft for the outside wall, 

Thicken.

Adjust end faces as necessary.

There is something wrong with the outside curve, had to use the inside curve.

Might help….

[eSonOfAnder]

Yeah, the problem with the outside curve is that it was created as an offset from the inner ellipse, and when you trim an offset ellipse, it creates a break at the major axis radius (This does not happen when you trim a segment from an ellipse created with the ellipse tool, which is why the inner curve is a single piece). I also saw one other minor difference between my example file and the original - the two starting points for the lofts were straight lines, therefore were planar surfaces, but in my actual design file, they are curved segments where the ellipse had been cut by a circle not a straight line. That really appears to just throw a huge spanner in the works. I tried out the surface loft, and it gets as close as I've seen so far, but for whatever reason, it curves downward towards the outer edge of the ellipse before then angling back up to the endpoint, and I cannot see any particular reason for that.

[davebYYPCU]

Not here.

Might help...

[eSonOfAnder]

If you're still using the first f3d file I attached titled Loft Example, then yes, it works just fine there because the two end segments on the far end away from the circle are straight lines. If you look at the new file that I attached, you can see that if those segments are curved where the ellipse has intersected with a circle, it does the dipping down before curving back up thing. Basically, this only ever works if one end or the other is a planar surface; they cannot both be curved faces. I used the point along path tool to find the midpoints of both the inner and outer curve to create a straight line, and extrude a planar surface up; since I knew it was the midpoint on both curves, it would also be the midpoint in elevation. I could then use that planar surface to do lofts in both directions and ensure a smooth incline from beginning to end of the full face.

TL;DR Fusion really does not like working with non-planar surfaces.

[davebYYPCU]

You may be suffering an illusion, the Loft running from each end, is on a taper, I do not see the dip lower in height except for the lowest profile.

Edit the solid loft, remove both rails, and replace with a centreline rail off the good ellipse.

Looks Ok to me.

[eSonOfAnder]

No, it's not an illusion, you can see in this screenshot with the upper and lower curves selected that the minimum distance between them is 2.4mm for a loft that is going from a 3mm tall face to a 5mm tall face. It is sloping down and then back up.

I redid the solid loft like you described and switched it to centerline instead of rail, and that does somehow work. That doesn't even make logical sense considering that line is at the edge of the faces being lofted, not the center, but the important bit here is that it works. You can see in the new screenshot the difference between attempting to use the surface lofts and the "centerline" solid loft.

[davebYYPCU]

Centre line works, because you have not got enough rails for the other version. (Normal rails)

To use normal rails, you will need all 4 rails, each corner of the profile.

(I encountered bad geometry from the outside ellipse - offset yep known reduction of quality)

You are correct the curved face profiles are contributing, but the centre line rail behaves correctly, no surprise to me.

I could not find the dip because I used the centre line.  Catch 22.

Might help....