Using interpart expressions

[SiW979]

I've always been very cautious about using interpart expressions, I only really use them between the master model and associated drawing in order to dispay a components weight etc. Am I right in thinking that unless you work in a super close knit engineering team such as F1 etc, they are just to dangerous to use to control component form? Also I have recently found them quite useful for specifying distance mating conditions (referencing a material thickness in another part in order to positon a washer by distance correctly. Is this wise?

Any thoughts anyone?

many thanks in advance

Simon

 

[hudson888]

Recalling (not personally) events surrounding how the Arrows F1 team demise unfolded maybe I'll just leave that aspect alone.

I have used interpart expressions in the past for passing parameters between files. Part deformations do something similar in a more manageable and reliable way after a fashion, (that is they do more than just interpart expressions). Anyway both of these methods work well enough. The consequences that come about if upon loading the assembly a vital part cannot be located are usually minor; just a warning message at most. You have the opportunity to remedy it quite easily by manually loading the missing part for example. So for all your purely geometric needs it works pretty well.

You used to have to load components fully and/or avoid partial loading of you used interpart expressions under earlier versions of NX. I think that ticking "load interpart data" in the load options may alleviate that, but I'm not entirely sure if it deals with just wave data or picks up on linked expressions as well.

You might want to test this, and I know it is a bummer if it proves to be still a problem, but we previously stopped users from adding assembly weights to the drawing in the manner you described. The reason was because whenever a component could not be located the drawing would refuse to allow you to open it. This was being done by taking a body measurement to store the mass data under expressions in modeling, and using that as relationship based note on the drawings in the form of "<X0.2@mass> Kg". Now I have just tested one of those old drawings in NX-5 and it appears to be perfectly stable. Being able to report mass in this way is a pretty desirable thing so I'd do it anyway with the proviso that you can always delete the mass notes if they start to cause problems.

For the non-cumulative masses of individual components we just use the parts list.

Best Regards

Hudson

 

[SiW979]

Hudson

Once again thank you for your time and information. Because we are so 'scared' of the potential problems this could cause, I haven't really looked into interpart expressions very much at all. One of the problems we have here is that we have a very broard spectrum of NX competance coupled with the fact that engineers roles hear are very fluid and people tend to flit about all over the place where as within other oganisations people tend to stick to owning one area of a machine. Some one could theoritcally design something with interpart expressions quite successfully, release the part and then move on to another project, then someone else may come along and make a mod' to the part which contains a referenced expression and they me not have the experience of foresight to check for IPE's, then they release the part and not realise that they have affected another part without knowing, then drawings and CAD models are suddenly out of sync.

Dooom!!!!!!

 

[hudson888]

Simon,

I know we'll all try to fight it but sooner or later you can't avoid that some of your data becomes your legacy. Something that has to be maintained against your fervent wishes to have everything ideally constructed. The virtual ideal mindset that flows from anything CAD or computer based turns out to be somewhat elusive. That human nature prevails to reveal the frailties of even the data that we create is probably at least a positive in that it belies the ability of technology to dehumanize us.

Regards

Hudson

 

[DavidTolsma]

Interpart expressions are great if used consistently and cleanly.

What I mean by this is to drive expressions down, but not rely on expressions. So override expressions in components but not link expressions in a higher level.

I've found that to work best and less likely to fall apart. Deformation parts and other core NX features make this less necessary. Others just like to link what ever and in any order. It would work until you try to reuse it another assembly or make any large changes.

-Dave Tolsma
Tolsnet LLC

http://groups.google.com/group/NX_CAX/

http://groups.google.com/group/plm-exchange/

 

[hudson888]

Yes when you use interpart expressions to override you are effectively creating a context which applies differently depending on how the components are loaded with or without the assembly. Generally I'd say that this is an intended consequence, but one would have to argue that in most cases the part deformation may be a better choice. The only drawback with part deformation as I see it as that it can be recreated but not edited.

As with all things keep it simple. You can create a tangled web of interdependencies that serve no positive role in maintaining your design successfully. I would even go so far as to admit to doing so, but in layout work rather than final released designs. "Horses for courses" as the saying goes.

Regards

Hudson