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12-26-2017 08:16 AM

Hello everyone!

I am working with a part geometrically similar to the one attached below.

The problem here is I have two options to get the required surface (there are many others as well, but these match very closely with what I require).

So, essentially, I am trying to get a surface created from a set of curves. Now fill surface in this case seems to be a faster way to achieve the result compared with through curve mesh. On the other hand though, through curves mesh takes time (just a little bit more) but the end result is very different.

__Why are the results different? That's my question.__

I have kept all the parameters almost identical.

Check the part files attached & these pictures for reference.

Thanks in advance.

NX 12.0.2

Solid Edge 2019

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7 REPLIES

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12-26-2017 09:39 AM

There are thousands of shapes of surface that will go through those curves. Each surface command will use a different mathematical method, plus in your case different input constraints were defined.

Actually looking at the construction the input curves do not look right to me. You appear to be trying to define the answer in sketched analytical curves rather than the problem that is to be solved.

What is the design intent, what are the design constraints? Sketch, preferably with simple splines or just lines what is needed and fixed. Only the absolute minimum of what is required. Then can advise on the best construction method.

Steve V

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12-26-2017 11:37 AM

I'll try to answer your questions,

*There are thousands of shapes of surface that will go through those curves. Each surface command will use a different mathematical method, plus in your case different input constraints were defined.*

- Yeah, I understand that very well. There can be many solutions to even just a simple set of curves, and it all depends on the command being used and the constraints. And my question, in a way, can be considered against the mathematical (or functional differences) between the above two commands.

*Actually looking at the construction the input curves do not look right to me. You appear to be trying to define the answer in sketched analytical curves rather than the problem that is to be solved.*

- As I stated in OP, this is not the actual design I am working on but it's very similar. That too uses simple analytic curves (arcs, lines, etc).

*What is the design intent, what are the design constraints? Sketch, preferably with simple splines or just lines what is needed and fixed. Only the absolute minimum of what is required. Then can advise on the best construction method.*

- One of the thing I need maintained in the resulting surface is the G1 continuity at all the curves. I can neglect others. I found fill surface to be very efficient when tackling these kind of problems. But through curve mesh is more 'robust' and gives me more control over the output surface.

If you notice the output surface (in case of through curve mesh), you will notice that just before the corner curves (curves passing through the Datum CSYS origin), the surface is changing its curvature (there's a bump). This isn't the case with fill surface.

It would be great if you can point me out what should I change in fill surface to get the same output as through curves mesh or the reverse if former isn't possible.

Or If you can explain with some example where these two functions are viable, it would be even more better.

Thanks.

NX 12.0.2

Solid Edge 2019

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12-26-2017 12:09 PM

Through Curve Mesh creates an untrimmed surface based on four edges, in your case one edge is a point. It will use the curve to create the maths of the surface.

Fit will create a trimmed surface that passes thought the curves selected. Uses the curves just as target reference.

To see this switch on the surface poles or change to static wireframe and modify the surfaces to show u v lines.

Steve V

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12-26-2017 12:27 PM

Back to the construction task.

Does the part need to have straight edges for the triangle?

Do the corners of the triangle base really need to be fixed radius arcs?

Does the dome have to go exactly through the common topic point?

Does the dome have to be precise a radius cross section at the cross lines?

Removing any of these constraints will make a smoother surface.

Free-form surfaces are best constructed from splines.

May get better result and control if build with individual surfaces then.

Have done similar parts in the parts. Method used was to sweep curve along each side of the triangle. Revolved a top face. Trimmed and attached the four surfaces , added bounded plan base then blended the sharp edges.

Yes a different shape, but hopefully get the point, minimalist curves. Describe the intent not the answer.

Steve V

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12-26-2017 12:35 PM

I completely agree with all he writes, more I suggest not to mirror the surfaces even if symmetrical.

N-Side Surface is another command that can help you. It requires one or more control surfaces (in my case a Law Extension) and a set of curves (Outer Loop).

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12-27-2017 03:01 AM

@StevenVickers wrote:Back to the construction task.

Does the part need to have straight edges for the triangle?

Do the corners of the triangle base really need to be fixed radius arcs?

Does the dome have to go exactly through the common topic point?

Does the dome have to be precise a radius cross section at the cross lines?

Removing any of these constraints will make a smoother surface.

Free-form surfaces are best constructed from splines.

May get better result and control if build with individual surfaces then.

Have done similar parts in the parts. Method used was to sweep curve along each side of the triangle. Revolved a top face. Trimmed and attached the four surfaces , added bounded plan base then blended the sharp edges.

Yes a different shape, but hopefully get the point, minimalist curves. Describe the intent not the answer.

All points but the fourth one are important and need to be maintained as given in my sample part.

How can I remove the irregularity of the surface when it passes through the cross curves (while using through curve mesh) to make it, to an extent, visually smoother.

Your example gave me some good points. Will keep those in mind.

Thanks.

NX 12.0.2

Solid Edge 2019

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12-27-2017 03:03 AM

I needed an extension surface as well, later on. Law extension will make things easier.

Thanks for the advice.

NX 12.0.2

Solid Edge 2019

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