Next shell question..

chriss_ko

Hi *,

I have two lofts following two 3D fit splines and I want to transform them into a "pipe" with the shell function. That works with one of the two but the 2nd looks a bit strange:




Closeup:



Here is the sketch:


Here is the link to the document:
https://cad.onshape.com/documents/fa4bce245ef9d6596f869a94/w/2937cd3cfb02db366ad4770f/e/d8de7c90881730ef750c7d2b


Cheers, Chriss 

chriss_ko

S1mon said:

Can you loft the square profiles and then add fillets after before shelling? Loft or sweep can often create funky surfaces.

I'm not sure what you mean with "loft" in this context? "Base" where the two "horns" are starting is a separate part till I merge the three.

The "horns" are 0.8mm now, I think that this will be robust enough anyway. But I'm always open for new/better techniques to solve that problem. This will not be the last part where I will have this problem.

nick_papageorge073

Well, your general approach to the shape is much times better than the last one:) Good job.

nick_papageorge073

It might help if the profile you draw for the loft is more perpendicular to the path curve. Right now it is very angled to the path curve. You can draw it perpendicular, and make the loft longer. Then trim the loft to the desired angle with a split feature.

As before, any problems with shell have to do with the root outer surfaces. In this case, you are asking the outer surfaces to follow your loft path, twist along the way, end at very sharp angles, and change radius along the way. This all can cause funny defects in the surface, especially when the surface is offset, which is what the shell does. If you make the twisting more "gradual" that might solve the issue. That's the idea with making the end profiles more perpendicular to the path curve. It will make all the twists more gradual.

You may also solve the problem simply by changing the radius at the profile rectangles.

chriss_ko

Thanks Nick! I really appreciate your input. You are right, it is the far better way, but I have to admit that I have stolen it from a other dude. But I think that this is normal, isn't it?

> You may also solve the problem simply by changing the radius at the profile rectangles.
I do not think so to be honest. The other "horn" the same radius, bend etc but not that "problem".


Anyway, I still do not understand why it is working at the "right" side but the left side has this problem. I made a new face which is perpendicular with the other sketch for testing and the duct does not nor at all anymore. That made me give up for now. I will clean up the sketches on the "Connector" part first. I have the feeling that the multi use of one sketch brings in a unnecessary complexity.  I will come back later.....

chriss_ko

The current solution does not make me very happy to be honest. I think that I will add a 4th point the left curve to change the angel more perpendicular to the starting sketch. The "start direction" modification did not help my in my case unfortunately.

S1mon

Can you loft the square profiles and then add fillets after before shelling? Loft or sweep can often create funky surfaces.

[edit] Looking at your model quickly, I wonder if you tried adding connections in your lofts? You might get something more like what you intended.

chriss_ko

S1mon said:

Can you loft the square profiles and then add fillets after before shelling? Loft or sweep can often create funky surfaces.

I'm not sure what you mean with "loft" in this context? "Base" where the two "horns" are starting is a separate part till I merge the three.

The "horns" are 0.8mm now, I think that this will be robust enough anyway. But I'm always open for new/better techniques to solve that problem. This will not be the last part where I will have this problem.

glen_dewsbury

Here's a sample that may help to simplify using surfacing tools. I found that your radii had to be reduced to make this method work. The original filets over lapped  at locations along the sides. I'll leave you to determine if variable fillets can be adjusted to sizes you like.
https://cad.onshape.com/documents/a06a050f379f472ab93ce664/w/9707f8de7e7b36c8cb97e42b/e/86e6c3a26f490355765c7ee8

chriss_ko

I think that we close this case. I relocated the pints which guide the splines so the shell is smooth now and I was able to make it 1mm now. Thanks for your help guys.

S1mon

Here's another approach. I got rid of the center paths, simplified the loft sections to rectangles, created 3Dfitsplines through the rectangle corners, and added variable rounds after lofting (plus some other fixes).

https://cad.onshape.com/documents/2be4bde2e50306b735cfe9d6/w/30cc517f709a327a57d80695/e/80cb090adf5914dedc3358f0

nick_papageorge073

What does this part do anyway? Cool prints faster/enable faster printing speeds? Are you trying to make a better design? Or are you trying to save money and not buying one off-the-shelf? I'm only curious your reasons for designing and printing rather than buying.