topic Re: Chain selection doesn't seem to be always working in Fusion Design, Validate & Document Forum

Chain selection doesn't seem to be always working

gamelife4dns — Fri, 25 Sep 2020 14:04:16 GMT

Hello,

I can't use the "chain selection" in some strange circumstances.

I attached a f3d file. Please try to make a pipe by selecting the (obvious) path at once from the whole waved spiral projection of the latest sketch.

Thank you.

Steve

Re: Chain selection doesn't seem to be always working

ritste20 — Fri, 25 Sep 2020 15:16:36 GMT

So I think there are a couple of things going on here that would prevent the chain selection from working. See the images and descriptions below.

First off, Sketch 1 you have geometry drawn in 2 planes but it was not a 3D sketch. That is asking for trouble down the road. So I split the YZ geometry with your upward arc into a separate sketch and was able to fully define it with your parameters.

The next thing I did with your mirror function was to change the mirror objects to features which prevents the lofted surface from "flipping normal" and putting the top of the plane on the bottom if that makes sense. Then all good up till the stitch operation. This is when I noticed a small overlap between the patterned features.

After the stitch, and I'm assuming this is from the overlap but it again flips the normal side of every other surface as well as creates a disjointed path in your final sketch.

Chain selection requires a perfect tangent condition of an unbroken path. Something else I am suspect is causing issues, are your 3 profiles for the original lofted surface. Because they are constructed on 2D planes and do not follow the contour of the "would-be" radius of the spiral at that location, they are not a true projection of the profile and maybe causing the overlap as well as additional problems with tangency conditions. This is not a terrible thing to fix but it would probably involve a surface extruded at the radius curvature for the centerline of the path, and using "Create->Project->Project to surface", then lofting through those profiles instead of the 2D splines.

Back to your original question, I was able to place a round profile at the inside beginning of your spiral in the original version of the file and select sequential path segments so the mismatch must be small enough that the sweep function can still solve it but it cannot recognize a continuous path from those sketch objects.

Hope this helps,

Re: Chain selection doesn't seem to be always working

gamelife4dns — Sat, 26 Sep 2020 16:22:49 GMT

Thanks a lot for having looked into it so deeply.

I guess I was making some assumptions about the Stitch feature. I thought the feature would manage any (small) gaps or (small) overlaps the “best” it could, with a smooth result. So I left approximate 2D profiles drive a Loft to obtain a quite close surface of the “would-be” as you say. Bad assumptions.

So indeed the issue is the Stitch which isn’t as smooth as I thought, and my profiles.
I solved it (attempt) by skipping the Mirror feature (of the “half wave”) and making the Circular Pattern directly. This results in missing surfaces in the resulting rounded shape. They are modeled with a couple of features, a Loft (between 2 surfaces now, G1 option) and a Circular Pattern of this Loft.

A note about sketches which are always 3D as I understood. I think it was Jason from Autodesk who explained it in an advanced sketching webinar. The 3D checkbox is there only to show or hide the 3D manipulators.

Solved, thanks again !

Steve

Re: Chain selection doesn't seem to be always working

ritste20 — Sat, 26 Sep 2020 17:01:36 GMT

Yes, the sketches basically are always 3D as you say, but I still try to limit sketches to 2D geometry whenever possible. 3D sketch geometry opens up a whole new can of worms if you don't know what you're doing. I'm not calling you out, just saying in general the simpler the geometry, the more options available when it comes to the 3D creation commands and manipulating the model in the future.

I'm glad you were able to make some improvements and get it modeled.