Override Density for COG calc... old post

[cbenner]

Hey gang,

Several years ago... may 4 or so, there was a post about some back calculation you could use to modify a parts density (?) in order to get the mass to a specific number.  I believe it had something to do with the manually overridden mass not facturing into COG correctly?  Does anyone else remember this?  I've been trying to find that old thread with no luck.  I'm mainly just curious now that it's in my head.... did I imagine this?  Is this just an AU hangover?  

[mcgyvr]

maybe one of these?

http://forums.autodesk.com/t5/inventor-general-discussion/edit-center-of-gravity/td-p/5380381

https://forums.autodesk.com/t5/inventor-general-discussion/override-cog/td-p/2011121

[cbenner]

Nope, I saw these two.... I'm beginning to think I imagined it.  I think it would have been around 2011 or 12.... ish... or not at all!  

[cbenner]

Never did find that old thread, but I found one that triggered a memory of how they described doing it.  I'm fairly certain the author is now an EE, but since I can't find the thread, I can't prove that.  LOL

The situation involved a dummy part from a vendor that was basically a solid block, internals not modeled (a valve for example).  The weight was known from the catalog, but the density was based on the "Default" material.  Density is what is used for calculating COG, so just overriding the Mass in the iprops would not give an accurate COG.  The solution, if I remember correctly was to divide the known Mass by the volume of the modeled part, and then manually ocerride the density with this result.  That would adjust the Mass in the iprops, and give atleast a better COG calculation.

Anyone remember this?  

[blair]

That would work as well.

Or create a new custom material with the required Density to acheive the Mass.

[cbenner · Accepted solution]

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@Anonymous wrote:

That would work as well.

Or create a new custom material with the required Density to acheive the Mass.

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That actually may have been a part of the original solution.  Just wish I could find it.  BTW... I've been playing with it, and this does work.  If you know the weight, but the part is not an accurate model, forcing the density based on d=m/v will give you the correct mass, AND correct COG.

Very handy with third party "dumb" models of purchased parts.

[cbenner]

Follow up....

Applying this method to Content Center parts used in Tube & Pipe.  As always, when modifying CC parts I open from CC and save as custom.  Make the changes to the density and the weight (Mass) changes accordingly to be what the weight needs to be.  Save the part, Replace Family Template in CC.  Template replaces successfully.  Save my assembly and Refresh standard parts, the modified part shows up as needing to be refreshed.... as expected.  Refresh is successful.  Check iporperties in the part in the assembly..... and the weight is back to what it was before I did this exercise.

Can this NOT be used to change the density of CC parts?

[blair]

You would think so, sounds like an "issue", where it's reverting back to the base CC item's materials.

We always save CC as custom and then into our Work folder. Any changes to the material should reflect in a Rebuild All which should then correct the COG.

I don't create any CC item that's not a "Custom" item.

[gavbath]

iLogic rules do run in Content Center parts, so I'm just wondering if you created the override formula you need in a "custom" cc part and replaced the family template with it, would that do what you need?

[cbenner]

Workaround seems to be to move the actual part file out of CC folder to a work folder. Make the change and then move it back. What a pain.

[blair]

Or create as a Custom and save directly to the Work Folder or Library Folder and never put it in the CC folder.

[blair]

Remember that CC items can be refreshed, this means that the material physical shape will be updated from the Family Table. Using the Custom option and placing in the Work Directory breaks the link back to the Family Table. Just using the Custom and saving to the CC Library won't break the link, any CC Refresh will over-write any manual edits.

This seems to be what is happening to your items.

[cwhetten]

Was it this one?    Your post triggered a vague memory, so I had to start digging.

As for he content center issue, even if you modify the template material style, when you place a part from that family it uses the material definition from the styles library.  So if there is a material in the library with the same name, it will use the library definition instead of the locally overridden style.

I haven't tested this, but maybe if you define a new material style in the template and set its density to the desired value, it might work.  The important thing here is that this new material style can't have the same name as an existing style in your library.

It's worth a test to see if it works.

Cameron Whetten
Inventor 2016

[blair]

Cbenner was fighting the same issue with CC items in T & P. If you change the Material in a CC item it will work for a while until a Refresh is done. Then the Material reverts back to the CC Family Table.

The best would be to place another instance of the CC item from CC and use the Custom Option. This will save it to your Work Directory and break the link back to the Family Table. This will allow any Refresh of CC not to affect the part.

Part of the benefit and curse of using CC items and keeping them as CC items.

[cwhetten]

I tested my idea and it works.  My description was probably not very good, so I'll give it another try:

1. Place a part from the family "as custom" in a non-library folder.

2. Open the custom part for editing.

3. Create a new material style whose name does not match any materials in your library.

4. Set the new material density as necessary to get the desired calculated weight.

5. Save the part.

6. Open the content center editor and find the family.

7. Replace the family template with the modified part.  This will load the custom material into the family definition.

8. Set the material column of the family table to use the custom material (it doesn't exist in your material library, only in this family, but it should be available as a choice alongside all of the library materials.)

Now, when you place a part from this family, it will have the custom material style with the adjusted density--therefore, the adjusted weight value.  This method is immune to the refresh issues mentioned because the custom material is part of the family definition, not just a local modification of the placed CC part.

The only drawback, of course, is that your BOM is going to list the custom material, whatever you named it, instead of one of your library materials.  This might be a big deal or not.

Cameron Whetten
Inventor 2016

[blair]

You shouldn't need to worry about the Family Table is the CC item has been saved as a "Custom" to a non-library folder. A simple change of the Materials or override of the Mass is all that's needed, or a custom material to get the Mass required.

[cwhetten]

My suggestion is good if you want to build it into the family so you don't ever need to manually modify the parts again.  Even if you want to always place them 'as custom', my trick saves you from modifying the custom part every single time you place one from that family.  You just do it once and never worry about it again.

I guess I am assuming this content center family will be used over and over again.  If it's just a one-off oddball part, then my suggestion isn't helpful.  But I could see this being useful on a family of valve parts.  Because valves are really assemblies, it is difficult to get their calculated weights to come out properly from the content center.  So my suggestion would let users continue to place these 'as standard', but the weights would be closer to the manufacturer's published values.

Either way works, just depends on what you need.

Cameron Whetten
Inventor 2016

[cbenner]

@blair, @cwhetten  I had no idea you guys were still going at this discussion... sorry.  What's been working for me is to move the part OUT of the CC folder to a working folder.  Make the changes I want, them move it back.  Old school but effective.

For simple geometry changes, the method of placing as custom, changing and Replacing Family Template works just fine.  But to make changes that will be reverted back to defaults based on the part template (such as physical properties or material properties etc... the old school method is working.  I also use this now to break the link of derived parts to their parent assembly... this was causing me a lot of "resolve" errors in the past.

Thanks for keeping the discussion alive.

[blair]

We want to beat it to death, we only have limited time before the year runs out or we get a private message from the forum mediator and our account is frozen. 🙂

[Curtis_Waguespack]

@blair, @cwhetten, @cbenner

So we just looked into this issue again this past week, and for our setup there was Vault to deal with. The concern was that if the CC member was modified and then checked back in, someone could then accidentally check it back out, refresh, checkin, etc., and step on the data. So the plan is to setup a "Librarian" vault user that keeps these parts checked out.  But this thread gives us some other approaches to consider as well. So thanks to each of you for the contributions to the discussion.

My question to anyone interested in this topic would be: is there an IdeaStation idea to come out of this? Ultimatly, it seems that it would be nice to be able to "fudge" densities in the CC family tables, so that we can stock our libraries with purchased components that do not need to be modeled in detail, but do need to have accurate weights.  Any thoughts?