Lofting with point profiles fails on rails. G1 discontinuity in a curve

[jpberti]

I'm trying to create sharp and controlled automotive fairings in Fusion 360.  Starting to get some good success using precise rails and profiles and Lofting in the Patch workspace.  In this example I am trying to put a divot feature into a shape I cut from the hull.   The hole was cute by projecting a spline sketch into the face.  

I created two sketch splines in the hole that attache to the hole rails, to create the clean and controlled divot shape.  It almost works.  I can get the loft to continue from point 1 to midway profile to end point.  It fails though on attaching the rails.  I split the oval sketch on the face into two separate splines that begin and en on the end points of my loft.  One rail works fine, and then second fails with the G1 discontinuity.  

Can you explain why this is, and what can be done to fix it?

I really want to maintain this sort of control in my organic shapes, using carefully placed guid rails and profiles, and not go into the sculpt workspace, which I find to "mushy" for my purposes.  

In screen shot below is the last place before the fail.  Fails when adding rail on top of hole.

To try to isolate the problem further, I split up my ellipse rail into 4 sections.  Then tried to loft the left and then the right side of the divot shape.  It now only fails on the top right rail.  In my original drawing of the spline ellipse, that would be the first part of the drawing.  So maybe the G1 problem to do with being anchored to a start point?  Don't know.  Please help.  I keep trying to redraw the ellipse and break it up.  But nothing is fixing the problem.  

[cekuhnen]

can you share a stripped down version?

email: info@ckbrd.de 

[jpberti]

Thanks.  I've attache the Fusion350 file here.

[cekuhnen]

@jpbert I think there might be some loft issue at hand here.

I tried this approach ring loft to point + 4 rails (broken splines / arcs) and it worked in a different file.

so when I tried it on the actual file you send me I experienced the same errors with new sketches I created!

I attached the file. Some AD people should maybe join here!

Can you instead of using this loft construction work with a carefully placed ellipse solid and trim the car side with it?

in trans design I prefer working with overbuild surfaces.

[jpberti]

Thanks for the careful examination of the problem.

I know the overbuild and cutting in techniques, but i find they both lack the sort of precision I'm looking for. It's very hard to place a contour line by massaging 2 planes to intersect precisely.

Maybe Fusion is incapable of this sort of modeling. I'm hoping to find a way through it. Any ideas or examples are very welcome.

Sent from my iPhone

[wilkhui]

Thanks, we're looking in to the failures.

Indy

[cekuhnen]

@wilkhui

could you look also into this?

http://forums.autodesk.com/t5/design-validate-document/another-loft-failure-or-bug/td-p/6494943

[wilkhui]

I'll do my best, give me a nudge if I'm taking too long 🙂

Indy

[Anonymous]

I know this thread is a year old. But I'm running into exact the same error when trying to work with the Loft tool on surface projected curves. Any progress on solving this issue?

Thanks

[cekuhnen]

@Anonymous

from what I can gather AD positions Fusion for mechanical design and such surfacing objects do fit less into that area and thus Iassume’will receive less

bug fixing. Some of those sketch bugs are up to 2 years old. Sucks for all the designers that thought fusion will be the next Design platform.

[Anonymous]

It additional sucks, because AD canceled support for the Rhinocerus T-Spline Plugin. (The reason why I changed to Fusion). Now I guess I will go back again (lot of other problems with Fusion too), and just build my T-Spline bodies in Fusion and export them to Rhino. 

[cekuhnen]

@Anonymous

I understand your concerns few points to consider

Rhino has no construction history which is why i

moved from Rhino to Fusion. The timeline is a great

idea and the simplified set of surfacing tools makea

working in Fusio i feel more productive.

However the amount of bugs in the sketch engine

and certain lack of modeling tools simply make it in some

cases problematic to use. Some bugs you can workaround

but sometimes you cannot.

T-Splines was great when it came out but to be honest nearly

every cad app has a similar tool and to be honest t-splines today

is the slowest one among all. Compare fusion vs solidthinking

for example to see the speed difference.

the nurbs quality that is produced later tho is what is also important.

I feel AD with Fusion is not focusing on designers anymore and misses

out on great opportunities. However if one checks solidworks you also

will find many problems too.

so I guess we are back again at doing surfacing in a surface app like

rhino and use a parametric modeler like Fusion to create the solid model

but not create the a surface.

Many companies still work that way even Apple.

so for you you could go back to Rhino and use the upcoming subs tools

and use fusion for the rest.

cam and sim in fusion is pretty strong by itself.

instead of Rhino maybe look into solidthinking which I find is much

better than Rhino for surfacing and digital exploration of ideas in general

because it is fully parametric which Rhino is not at all.

so you work in ST a lot more efficient unlike Rhino where the lack of Design history

forces you to use labor intensive workflows when exploring ideas.

[Anonymous]

Thanks a lot sharing your expierences. Just not always the decision is free, which software to use. Especially when the customer pays for it. 😉

[cekuhnen]

@Anonymous yeah hence my curiosity why such problems are not addressed to as this would open Fusion to a pretty diverse field

of commercial users too.