Grounding vs. constraining in an assembly

[cadranger]

I've recently started at another company that uses Inventor (v.9) and they do things with Inventor a little differently than my last company. In particular, when the first part is placed into a new assembly they leave it grounded and then constrain other parts to it. At my last company we turned off grounding and constrained the axis planes of the first part to the axis planes of the assembly. This achieves the same effect but begs my question. Which method is the best method? To qualify it better, which method will give the assembly more integrity and allow for easy editing (making use of parametrics because this is why we're using the software in the first place). I support the constraining of the first part because you can alter the orientation of it in the context of where that sub-assembly might be installed just by editing the constraints. If the grounding is forgotten, your assembly might shift causing problems with .idw views. Another issue is computation time when dealing with large assemblies (this may or may not be a big issue any more). I'd like to hear some tried and true responses.

Cadranger

 

[DesignerMike]

I typically like to keep the first part grounded, and often times some other parts as well. Angle constraints still have the ability to flip un-expectedly which will really make a mess. I often times unground, constrain the first part to the origin differently, re-ground, and disable (or delete) the constraints to get the first part positioned in the assembly as I want.

The other reason to ground, is that a grounded part takes less computing time to keep it in place. Multiple constraints (especially redundant and conflicting constraints) will really slow up your performance.

I've been trying to make more of my constraints (escpecially angle constraints) to the assembly origin planes and axis. They seem to be more consistent.

 

[SeanDotson]

I agree with Mike's assesment.

Sean Dotson, PE

http://www.sdotson.com

http://www.mCADForums.com

CAD Professionals & Consultants Discussion

 

[cadranger]

Thanks for the input. I do agree that constraints should be simple and unambiguous. I always build my parts around the origin axis then project and use the appropriate origin planes to build my sketch. As you know, projected planes and other geometry can, but not always, be used for creating part features. Once the sketch is fully constrained, the part becomes rock solid. Next, the part in an assembly, I always do a Flush-Flush-Flush with the X,Y and Z planes of the first part in an assembly. That first part being, almost always, the most important base part. No grounding and imoveable. The three constraints with no offsets, I find, are very efficient also. I'd hate to forget to re-ground the part.
I have used alignment parts containing just construction planes and projected geometry in sketchs to align subassemblies in large assemblies. These alignment parts all share one common origin (like the cornerstone of a building) that allows for a simple F-F-F constraint for each subassembly. This works well for project teams to work separately but accurately within the context of a big assembly.

 

[cadmaniac]

Keep in mind that if you need the grounded part to interract and move based on physical dynamics, it won't. You will need to use constraints.

Anyone can be Captain in a calm sea.