Changing number of bodies causes update failure

[CNSZU]

Hello,

Suppose we create an extruded block. Next we create a feature consisting of 2 extruded holes on each side of the block. Now we make the first block the current feature and create a split feature splitting the body in half. After that we make the last feature in the part navigator the current feature. Now we have a problem. The last extruded feature of the 2 holes has failed to update properly, showing only one hole instead of two.

This behavior is strange and illogical. Why does changing the number or bodies cause the dependent features to fail to update? It is obvious that one hole is missing, why doesn't NX deal with this problem correctly?

This is only a very simple example, often when creating parts I will later change the design by splitting or merging bodies at the beginning of the part navigator. The problem is that every time I do this, I need to redefine every dependent feature and re-select the body which the feature is acting on. This is very tedious and time consuming.

What should I do to avoid this?

http://files.engineering.com/getfil...1-6462-4482-9f19-87ddaca0d2b8&file=Split1.PNG

http://files.engineering.com/getfil...f-1659-42c0-ac97-655a3ce501c2&file=Split2.PNG

NX8 Win7 i7-3770K@4.3Ghz 16GB Quadro2000

 

[JohnRBaker]

This so-called "behavior" is NEITHER "strange" nor "illogical". It's working exactly as designed and exactly the way ANY history-based modeler would work.

When the original second extrude was created and subtracted from the first extrude, there was ONLY a SINGLE body to interact with. However, when you went back and CHANGED HISTORY, by setting the first extrude to be the 'Current Feature' and then splitting it into TWO bodies, when you then set the second extrude to once more be the 'Current Feature' you created a situation where one of the bodies from the second extrude was no longer able to intersect with the what was NOW the first extrude. No mystery there.

As for what you should do, if you wish to take maximum advantage of the way history-based modeling systems work then the 'Split Body' operation needs to be performed AFTER the second extrude was created and subtracted from the first extrude.

Alternatively, if you really must be able to work in an environment where you will be going back and CHANGING HISTORY, particularly changing the number of bodies which downstream features will need to interact with, then I would avoid creating more than ONE body per feature, such as an extrude. In other words, the 'holes' really should have been created as TWO separate extrude features. Now granted, if you did this and then went back and performed the same 'Current Feature' change and performed the same 'Split Body' operation and then set the last extrude to be the 'Current Feature', you'd still get an update failure, but at least since there are now TWO extruded 'hole' features you'll be able to 'reparent' the one that failed by editing that feature, deselecting the original body and selecting the new body which was created as a result of the 'Split Body' operation.

And of course, there is always the option of using NX in a 'history free' mode where the order in which you create 'features' is no longer a limiting factor. Granted, the idea of 'features' and 'associativity' takes on a whole new meaning, but with judicial use of the Synchronous Modeling tools NX can still be a very effective design system even when working in a 'history free' mode.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
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[CNSZU]

Thank you John, for the comprehensive answer.

Well, I was hoping something like the option to select "all bodies in part" instead of a single body in the boolean section of the extrude feature. That way, the extrude feature would cut through any body(ies) regardless how the number of bodies is changed later. This also applies to the Unite and Subtract features. This would make it a lot easier to change the design at a later stage, which after all is what is great about history-based modeling.

NX8 Win7 i7-3770K@4.3Ghz 16GB Quadro2000

 

[JohnRBaker]

Unfortunately, while you can have multiple TOOL bodies, with a Boolean operation, you must have a single, explicit TARGET body. Actually the system is much more fault-tolerant than it was years ago when failed Booleans were a much more common occurance.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.