Feature Dependencies and Good Modeling Practices

[Joest]

When in sketcher and adding dimensions, SW seems to only allow dimensioning and adding relationships from edges instead of allowing you to choose an entire surface. This causes errors and can cause the model to fail when the edge is eliminated (i.e. adding a round or chamfer). Am I just a SW rookie or is there a way to constrain feature to more stable geometry such as planes like good modeling practices in ProE? BTW I am using SW2003. Thanks.

-Joest

 

[JNR]

In general you can dimension or make relationships to planes. Sometimes you need to select the plane in the feature tree. It depends on what you need. I find that sometimes it is appropriate to use edges and sometimes not. Due to the chronolgical nature of the SW database, even if you change an edge later, the original sketch will still be fine. It is only if you make an edit to something earlier in the file that you would have an issue. It should show up as a parent to the sketch containing the dimension or relationship.

John Richards Sr. Mech. Engr.
Rockwell Collins Flight Dynamics

A hobbit's lifestyle sounds rather pleasant...... it's the hairy feet that turn me off.

 

[TheTick]

If a plane is normal to the sketch then you can dimension to it. You can not pick a face to dimension from.

Your are right, dimensioning to a face would be more robust.

 

[Joest]

Thank you all for your input. I dimension to planes when they are available. My goal was to find a way to dimensioning to faces. TheTick confirmed that SW does not allow that. I guess I will have to live without it. There are pro's and con's to any software.

Cheers

-Joest

 

[JNR]

The reason is what TheTick indicated and I forgot to point out. The face would have to be A). perfectly flat (or maybe circular) and B). perpendicular to the sketch plane to make logical sense and give a non-ambiguous result. Planes are by definition dead flat. Surfaces would have to be interrogated on the fly to confirm they were suitable to dimension and would cause a real problem if edited later to change their shape or orientation.

John Richards Sr. Mech. Engr.
Rockwell Collins Flight Dynamics

"Heck, there are so many rules around here, it's hard to accomplish anything!" - Me.

 

[MElam]

As JNR stated earlier, SolidWorks features are time-dependant (ie, their "chronolgical nature&quot. One of our company's best practices is to keep all fillets/rounds at the bottom of the feature tree in order to keep the model from failing when edges are eliminated.
If a feature needs to be added later, use your roll-back bar. It's like going back in time!

 

[Joest]

JNR,
Yes, you are correct, dimensioning to surfaces wouldn't work unless A) and B) are true. SW will not allow these dimensions even when both condition true. In ProE, it is possible because it is a feature based software which makes it a more robust package. I'm not too concerned with it, it just good to be aware so I don't devote further resources looking for a way to do it. Thanks for the help.

-Joest

 

[CorBlimeyLimey]

Just as a mattter of interest, you can select faces when dimensioning a 3D sketch.

from Barrie, Ontario.

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[Joest]

That's good to know. Thank you for the tip. Do 3D sketches have any limitations (drawbacks) that would keep one from using them by default?

 

[TheTick]

There are some things you just can't do in a 3D sketch: sketching circles, equal length constraint, and symmetry constraint for starters.

"Great ideas need landing gear as well as wings."--C. D. Jackson

http://www.EsoxRepublic.com

 

[alexsasdad]

The main issue here is that SolidWorks is a surface based software, not feature based. Therefore you can't dimension from features. You can only dimension from edges of the surfaces that were created by the features and of course datums axis, etc.. If that surface or edge is removed by another feature later in the model, Solidworks can't figure out where the orignal surface or edge is. The original surface doesn't exist as far as SolidWorks is concerned.

This doesn't help but at least it may help explain why.

 

[Joest]

alexsasdad,
The fundamental issues are clear now. So far, not being feature based is the biggest (-) I have found about SW. are there any benefits to being surface based as far as functionality is concerned? It seem like it is done solely to speed up the software calculations and simplify the code. I guess this is what separates a mid-range application such as SW and a high-end package such as ProE.

-Joest