Assembly mass property incorrect

[pachubby]

Hi

I am having a problem with an assembly not showing the correct total mass of all of its components and sub-assemblies.  The value is out by nearly 20%, over 3000kg!  I have read through many of the related posts and searched the internet but I can't find out why the problem is happening, nor a solution.  Please help!

I have narrowed the mass discrepancy down to a derived part of a sub-assembly.  But this incorrect mass is only present when I navigate to the derived part's iproperites via the browser tree of the higher level assembly where I am having the mass problem.  It is as though the top assembly got some of its mass property information from a previous point in time, i.e. possibly before the derived part's mass properties were updated, and now refuses to look at the current information.

By the way, I have opened up and checked the mass properties of each sub-assembly and the derived part; and when opened individually these show as correct.  I have also tried 'Rebuild All' with no success.

Is it possible for mass properties in an assembly to become corrupted?

[CCarreiras]

Hi!

Already Update the mass in BOM? Try it...

Did you find this reply helpful ? If so, use the    Accept as Solution or Kudos - Thank you!

[pachubby]

Hi carloscarreiras8703,

When I open the BOM Editor all of the mass properties are correct on each row, i.e. the value shown is what I get when I directly open the parts/sub-assemblies and review their iproperties.

I'll point out that the iproperties of an assembly do not appear in its own BOM Editor.

In my top level assembly the mass is wrong in the iproperties

[swalton]

If you multiply the reported part volume and the reported part density, you get 6.9384kg.  Something weird is happing in the derived part. Is it all solids or are there some surface bodies in it?

It looks like the problem part was derived as a multibody solid.  Try deriving it as a single body solid and see if the volume reports correctly in the weldment iam.  You might try the same part in a normal assembly to see if works correctly in a new assembly.

[pachubby]

Hi swalton,

I agree something weird is happening.  But if I directly open the derived part; the mass, area and volume properties are correct (see attached).

It is only when I have the top level assembly open and via the browser, and I navigate to the derived part, RMB and select iproperties, do I get the incorrect information as per my first screen shot.

I thought on updating the mass of an assembly it references all of its parts in ther current state and displays a total, and then if anything changes you have to refresh this.

[swalton]

Did you try changing the derive? I don't think that this should matter, but...

How about deriving into a new part and using that?

Do you have any LOD or substitues set up?

How about starting a new assembly.  It is correct there?

Is it correct on another computer?

Can you post your files here?

Long shot, have your rebooted your computer and tried again? 

As you can tell, I don't have a good lead to try next so I have listed a few things to try to get it to work correctly.  You may get to start a support case and see what Autodesk says after they examine your files.

[pachubby · Accepted solution]

Wahoo! I have fixed the problem.  But thanks for the input guys, you have saved my sanity today!

To summarise the problem, my top level assembly was not refreshing/rebuilding with a true mass property because the primary sub-assembly and a derived part of a smaller fabrication inside that, were giving incorrect mass properties, causing the total mass to be wrong.

But the primary sub-assembly and the derived part were only giving this error in my top level assembly and not when they were opened individually or inserted into a new assembly.  And because the overall design was well advanced (i.e. drawings created, etc), the option of creating new assemblies/derived parts/drawings was not viable.

To fixed the problem I replaced the primary sub-assembly in my top level assembly with a random part off my hard drive, I then accepted the error messages about broken constraints, I then updated the mass properties and saved the files, I then re-replaced the random part with the primary sub-assembly, refreshed the mass properties and... voilà the true mass is shown!

[HUSELALU]

I have exactly the same problem. All subassemblies have the correct mass invidually and inside the BOM-list, but the mass in the top level assembly iProperty is wrong. It should be around 1800kg and it shows 27.000kg. So its a huge difference!

It must be some better solution than a workaround.

[Mark_Wigan]

p.chub thanks for your feedback,

i wonder please if you have time can you post us the screenshot of the derived part "physical properties" window / tab please? and also the same for the opposite handed part that was not see to be causing any issues.

Huselalu can you also post us the physical property snapshot of one of several of your parts please, especially the ones that you have found that are inconsistent like was in the case of p.c. above... ?

i am just a bit curious to see if any of the units of measure (in document settings) in the smaller parts or weldments were inconsistent and confusing inventor, but it should not have made any difference from what i have seen before now.

many thanks.

[HUSELALU]

It helped when I changed the "reference" files to "phantom" instead.