To Sketch, or not to Sketch

[phillpd]

In the attached image, you'll see 3 versions of the same model.

I'm looking for the simplest method of being able to vary the two cylindrical diameters, so that they are equal, or one (could be either) is larger than the other.

A cylinder, boss and 2 chamfers would work, but I'd then need to use suppression by expression for the chamfers, based on the diameters.

A sketch would be an option too, but what becomes of the edge that drives the conical face when the diameters are equal ? It does actual update fine, and the edge becomes zero length, but I don't know whether that's good practise.

Anyone have any ideas, or suggestions ?

http://screencast.com/t/VKe6NNkyB9L

NX 6.0.5.3 (NX 8 Testing)
Windows 7 64

 

[JohnRBaker]

OK, I used the sketch approach and while you may wonder about how the multiple sketch segments are merged into a single face, don't worry about it. NX was designed to work that way, that is, merging coincident faces into a single face when it's possible. The result is a perfectly valid solid model.

See the attached model. There are two user defined expressions, Dia_A and Dia_B. No matter what values you give them, the model should always be what you'd expect.

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

http://www.siemens.com/plm

UG/NX Museum:

http://www.plmworld.org/p/cm/ld/fid=209

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

 

[phillpd]

John,

That does appear to work okay. However, only while the sketch is internal. If you make the sketch external and the diameters to be equal, then the EDU dialog appears.

Ignoring the above, I assume from your model, that having a sketch object that is 0mm in length is valid ?


NX 6.0.5.3 (NX 8 Testing)
Windows 7 64

 

[JohnRBaker]

This is only an issue if in...

Preferences -> Modeling -> Edit

...you've toggled ON the 'Interrupt Update on Warning' option. However, if you had only toggled ON the 'Interrupt Update on Error' you would have NOT gotten the EDU dialog. What's being reported is that the sketch is 'underconstrained' which we consider as something that we will report as a 'warning' but not as an 'error'. That being said, since underconstrained sketches are perfectly valid, we decided that with sketches which are internal we'd take the approach that what you can't see won't hurt you anyway ;-)

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

http://www.siemens.com/plm

UG/NX Museum:

http://www.plmworld.org/p/cm/ld/fid=209

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

 

[phillpd]

That makes sense.

How about my last question with regard to a sketch object (in this case a line) having a length of zero.

NX 6.0.5.3 (NX 8 Testing)
Windows 7 64

 

[mmauldin]

Another option because I can't leave well-enough alone.

 

[JohnRBaker]

Like killing flies with a sledge hammer ;-)

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

http://www.siemens.com/plm

UG/NX Museum:

http://www.plmworld.org/p/cm/ld/fid=209

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

 

[phillpd]

John,

I'm very wary of underconstrained sketches ;-)

I'd updated an expression as per ... p33=if(Dia_A==Dia_B)(Length/2-1) else (Length-abs(p30-p31))/2

NX 6.0.5.3 (NX 8 Testing)
Windows 7 64

 

[JohnRBaker]

One of the virtues of NX is that underconstrained/overconstrained conditions, whether we're talking about sketches or assemblies, we will allow you to continue to work and we will guarantee that the model will be considered valid. Granted, you may wish to consider these as being undesirable, and we provide you tools to check what these status conditions are, but we will also NOT stop you from continuing to work or force you to resolve these anomalies if you don't want to. It's your choice to make, but is you choose to ignore them, so will we.

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

http://www.siemens.com/plm

UG/NX Museum:

http://www.plmworld.org/p/cm/ld/fid=209

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

 

[wmalan]

I would add that in the world of "done today is not soon enough"... I love having under-constrained sketches making valid solids!

--
Bill