Symmetric modeling in X-form?

[CNSZU]

I've been looking at Class-A surfacing techniques used by Alias Automotive and trying to use NX to accomplish the same tasks. Since Class-A modeling is essentially controlling the pole structure of 3D surfaces, the principles should be exactly the same regardless of software.

One obstacle I've come across in NX is the ability to move poles in a symmetrical fashion. See the attached image for what I'm trying to do. (The reason why it's done this way rather than modeling one side, then mirroring, is to end up with a smooth curvature across the center plane.) With X-form I want to move some poles (move by polygon, proportional) on one side, and have the poles on the other side move symmetrically with the center plane as reference. However, I cannot find a way to achieve this. Is this functionality not yet implemented in X-form, or does NX have other tools to achieve this?

NX9 Win8.1 64bit i7-3770K 16GB Quadro2000

 

[kapmnit123]

Hi,
As far as i know it is not there yet but it seems to be a good enhancement request for sure.
Optionally you can use STEP VALUE in MICROPOSITION for getting a quantitative measure of the movement and then apply the same to the other end.

Best Regards
Kapil

 

[KhimaniMohiki]

1. Divide the surface using Isoparametric tirm at 50%
2. Sew 2 surfaces back to gether to get 1 body with 2 faces
3. in X-form, under Face Finder tick Select Symmetric
4. Make sure you have at least degree 3 in the direction normal to the centre-line
5. apply a boundry constraint G2 at the centre line, whether that be U or V min
6. Edit poles as desired

Khimani Mohiki
Design Engineer - Aston Martin
NX8.5

 

[kapmnit123]

Thanks for this good tip Khimani....... Just to add
Since CNSU is on NX9 so he can use EDIT/SURFACE /SNIP SURFACE (with the DIVIDE option on in the setting) instead of the isoparametric trim.
Thanks and Best Regards
Kapil

 

[KhimaniMohiki]

Ive never used Isoparametric trim so not sure why I decided to write it, yeah I would use Snip or just divide face maybe.

Ive made a video but I cant directly upload so hopefully the photobucket link works

Khimani Mohiki
Design Engineer - Aston Martin
NX8.5

 

[CNSZU]

Kapil, using Micro Position Step value is a good idea, but is unfortunately not available for polygon move mode.

Khimani, your method is a good workaround. A drawback however is that you need to add lots of additional poles to create G3 continuity across the center plane using two separate surfaces. Also, because you freeze almost all the poles due to keeping G3 continuity, you lose the ability to edit a lot of the shape. Therefore you need at least two X-form features to edit the shape: one for editing the general shape with a single simple surface that extends across the center plane, and another for making detailed, symmetrical changes with two surfaces. It is a pain, but doable I guess.

NX9 Win8.1 64bit i7-3770K 16GB Quadro2000

 

[KhimaniMohiki]

Why not turn off associative freeform edit, why do you need to record the history of the X-form? I dont even bother with history anymore when surfacing, I use History Free Mode, then swith it back when im ready to make a solid part, any tweaks can then be made with ciative freeform edit OFF. Otherwise you will end up with a huge string of commands.

Working without creating features (either in history free or with associative freeform edit turned off) will allow you to work as one would in Alias/ICEM Surf/Rhino (ie Direct or Explicit surfacing), where you might perform the same commands over and over (X-form > Match edge > X-form > Match Edge > X-form > Match Edge and so on) until your happy with your surface, constantly monitoring your curvature combs and reflect line.

Regarding G3 continuity, you cant have it both ways, if you want to keep flow continuity you require a minimum number of poles, you could change the pole structure so they are closer to the centre-line, alomost like changing the magnitude? It sounds like you might be trying to get too much form into a single patch, if you dont have enough poles to get the required shape then create a new patch.

Khimani Mohiki
Design Engineer - Aston Martin
NX8.5

 

[CNSZU]

It has never occurred to me to use History Free mode. The one thing i disliked about Alias when I used it was the lack of history - when the model was finished and I wanted to change the overall size a little, there was no choice but to rebuild the whole thing. What I love about NX is the ability to turn on/off features or edit them to make modifications - and everything will magically update itself.

As for the G3 issue, yes, that is the problem with creating two patches instead of one. Alias has a wonderful function called symmetric modeling which can be turned on to constrain poles symmetrically, which allows you to create a single surface with the absolute minimum number of poles, and yet obtain perfect smoothness across the center plane.

NX9 Win8.1 64bit i7-3770K 16GB Quadro2000

 

[kapmnit123]

Hi CNSZU,
Please find a video attached herewith. I am not sure if this is an elegant way of doing it but i hope it can be replicated to some real patch editing also.
Sure if you find it too cumbersome then it would be good to initiate an enhancement request for the same.

As a user i can co-relate to with Khimani stated . I used to work on some other software for CLASS-A surfacing projects and most of the time i preferred creating the primary patch from scratch (deleting the old one) rather then doing re-editing. This sometime ensured that i keep my file size small and save me from any confusion from multiple copies. In addition associative free-form (or pole editing in general) is not common in most of the other software (probably NX is one of the few software to have this. It may be my ignorance but i cannot think of any other at the moment.)

But i also agree it comes in quite handy while doing a smart concept creation (you can keep multiple copies in the same model and it surely saves time if you need to add some feature up in the timestamp order before doing the x-form).

Thanks and Best Regards
Kapil Sharma