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# how Divide Face works

Genius

I'm a little confused about how Divide Face works.

Please refer to the example below.

1. Face_A is divided into two halves.

2. One half of the divided face is extracted to give Face_A_half_1.

3. Face_A_half_1 is untrimmed to give Face_A_half_1_untrimmed.

I thought Face_A_half_1_untrimmed would be identical to Face_A. But it is not.

6 REPLIES 6

# Re: how Divide Face works

Siemens Esteemed Contributor

Maybe if you read the documentation on Untrim it will help you understand the behavior/result of the command.

The Untrim command enables you to remove imposed boundaries and extends planar, cylindrical, and conical faces in the linear direction of the selected face.

It's not restoring the face adjacent to the one you copied using Extracted Face, it's extending the Extracted Face (and does so in both directions):

Regards, Ben

# Re: how Divide Face works

Genius

I tried "Trim Sheet". The result is same as that with "Divide Face".

Yes. My past understanding about "Untrim" was problematic. I thought "Untrim" would restore 100% the original boundaries before trimming/dividing. Now this is apparently wrong.

It's not restoring the face adjacent to the one you copied using Extracted Face, it's extending the Extracted Face (and does so in both directions)

To what extent would "Untrim" extend the trimmed surface? Thanks!

# Re: how Divide Face works

Siemens Phenom

Many surface objects are mathematically larger than what they appear.  That is they often extend beyond what would seem to be the 'edges' of the surface, but in reality these are what are called 'PC' curves which are used by whatever function was used to create the surface object to define the physical limits of the surface.  But as I stated before, the mathematical limits may be greater.  In other words, even a surface which from looking at the Model tree does not appear to be trimmed, might in reality be trimmed due to how it was constructed and the type of data used to create the surface in the first place.  When you perform a 'untrim' function, it's NOT undoing an explicit trim operation, it's actually removing ALL trimming operations, whether they were user applied or system applied.

If your goal was to return the original, as created, surface to the state prior to an explicit Trim or Divide feature was created, there are only two actions which will do that.  The first is the most obvious, simply Delete the Trim or Divide feature.  If however there is either the need or desire to retain the feature tree without disrupting any of the previously created features for whatever reason, you could try to 'remove' the Trim or Divide feature using the 'Delete Feature' function.  This adds a new feature to the feature tree which basically acts as if the 'deleted' feature never existed in the first place, but it will remain in the tree, able to be 'resurected' by simply Suppressing the 'Delete Feature' feature.  I hope that's not too confusing

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA

# Re: how Divide Face works

Genius

Hi @JohnRBaker   Very clear and thorough explanation. Thanks!

# Re: how Divide Face works

Gears Phenom

If you follow your second method and use Trim Sheet, there is no need to Untrim the sheet - just delete the Trim Sheet feature.

For me, Untrim (back when Isoparametric Trim/Divide was still around) was only useful when given a surface model and I needed to untrim a sheet beyond its original boundary.  The results were usually unpredictable and sometimes extending beyond what I know were the original sheet boundaries.

Tim
NX 11.0.2.7 MP11 Rev. A
GM TcE v11.2.3.1
GM GPDL v11-A.3.5.1

# Re: how Divide Face works

Genius

Hi @TimF   Thanks for sharing your practice and observation with Untrim!