topic Re: Shell works only to the outside after loft in Fusion Design, Validate & Document Forum

Shell works only to the outside after loft

MartinMajewski — Mon, 28 Sep 2015 06:56:28 GMT

Hi all,

I have an strange behavior of the shell operator after I created a (relative) simple object with the loft operation.

My loft object is build of three profiles. Each profile is a simple rectangle with fillets on each corner.

The first rect has fillets with 10mm, the second with 1mm and the third with 0.5mm radius.

The first profile lays flat on the ground, the second is 7mm above the first and the third is 1mm above the second.

I can not create a 1mm thick shell towards the inside direction, but it works towards the outside direction. Thinner shells seams to work, but I wonder why its not possible with thicker shells, because it is completely counter intitive. The error message doesn't help either.

Here are some pictures:

Re: Shell works only to the outside after loft

TrippyLighting — Mon, 28 Sep 2015 07:17:46 GMT

Try to increase the radii on your rectangles and see if that helps. To me it sounds like the inward shell would create self-intersecting geometry if it's 1mm thick but the smallest radius is only .5mm.

Re: Shell works only to the outside after loft

gautham_kattethota — Mon, 28 Sep 2015 14:29:38 GMT

Hi Martin,

When shelling inwards, the shell thickness could be greater than the radius of some of the fillet faces. Fusion detects this and removes those faces from consideration while creating the offset faces for shell. However, I can see a problem in a case I constructed based on your description. But the error I see with shell appears to be different than the one you see. There might be some other problem here that is leading to the error you are seeing. Would it be possible for you to attach your file so we can take a look at it?

Thanks

Gautham

Re: Shell works only to the outside after loft

MartinMajewski — Wed, 30 Sep 2015 08:14:57 GMT

Since the example above was meant to be an experiment for another design, I closed the design without saving. 😞

It took me a while to get another design that produces the same error, because it seams that it depends highly on the right ratio between layer distances, fillet radii and rectangle measurements. If not correct the error just says that no valid result was found for the shell width, but not that the topology has to be altered.

So here you have the example that produces the topology error message.

You have to apply the shell modifier to the bottom face and give it e.g. 1mm width.

http://a360.co/1YO3HXY

Martin

Re: Shell works only to the outside after loft

gautham_kattethota — Wed, 30 Sep 2015 20:45:31 GMT

Hi Martin,

The problem is the large transition loft has to do along the corners as it goes along the filleted corners - from 0.5mm to 1mm to 10mm. In simple terms, this results in the loft face having a "pinched" surface near the area with the smaller radii. Upon shelling this body, this area leads to problems with offsetting the faces.

One workaround that was suggested internally, is to build the body using two loft operations. One loft goes from the profile in Sketch 3 to the profile in Sketch 2. The second loft uses the end face generated by the first loft as its first profile and uses the profile in Sketch 1 as the second profile (turn off visibility for Sketch2 when you are trying to pick the face). And add tangency take-off (in the dropdown next to the profile in the loft dialog) for the face profile of the second loft. This results in a body that is more suitable for shelling. Even with this though, I am able to go upto 0.8mm shell thickness. Not the perfect solution for you, but hope it helps.

Doing the same steps in the other direction - from Sketch 1 to Sketch 2 to Sketch 3 leads to an error in loft. I have reported this to the relevant team.

Thanks for reporting this issue.

Regards,

Gautham