Mass properties differ in assembly and parts 1

[coolio63]

I am using SW 2010 and have come across an issue where I have 2 parts that I have assembled. Separately, the parts weigh 124 and 100 pounds respectively. But when assembled and mated together, they weigh 214 pounds, 9 pounds less than individually. Any thoughts? I am using this to do virtual testing and 9 pounds will make a difference.

 

[CorBlimeyLimey]

Has a mass property been assigned to the assy?

 

[gwubs]

Are you using assembly cuts? We have seen massive errors in mass calculations when using cuts in assemblies. The mass can actually increase when you cut away material!?!. How about configurations? Are you using assigned masses?

 

[rgrayclamps]

Hi, gwubs:

I use assembly cuts quite often, but I never experienced errors in mass.

Best regards,

Alex

 

[coolio63]

Limey, I'm fairly new to SW, but I guess I do not understand the difference in applying a material with mass to each part, versus what you mention.

Gwubs, There are no assembly cuts in either assembly.

 

[rgrayclamps]

Hi,

I am having an issue with "Save As" command. When I save an assembly model (*.sldasm) together with selective components, SW indicated that I saved them successfully. But equations I have in eithor parts' model or the assembly model do not get updated to file names of the new created assembly and parts.

When I use "Pack n Go", I do not have the issue. Did anyone experience this issue?

Best regards,

Alex

 

[rgrayclamps]

I'm terribly sorry. I accidentally replied my new post here.

Alex

 

[PhoenixDynamometer]

ooolio63,
The reason for asking about "Assigned Mass Properties" is that when you check that box CBL has shown in his picture, you can overide the actual weight of an item or assembly and put in a different weight.

http://www.phoenixdyno.com

Home of the world's most accurate and repeatable dynamometers, dynamometer accessories, and data acquisition & control software.

 

[CorBlimeyLimey]

Limey, I'm fairly new to SW, but I guess I do not understand the difference in applying a material with mass to each part, versus what you mention.

I was asking if a mass had been manually assigned to the assy. An assigned mass would override the sum of automatically assigned mass of the component parts. If a manually assigned mass has not been applied at the assy level, that eliminates one reason for the discrepancy.

 

[rgrayclamps]

Hi, coolio63:

Could you post your assembly models with components? Discrepanies in mass are not very likely.

Best regards,

Alex

 

[coolio63]

Nothing assigned in the assembly. I simply mated a test fixture to the top of a Media stand to determine that if placed on a 10 degree platform, would the CG be in front of the front leg.

 

[CorBlimeyLimey]

Are any of the parts, multi-body?

 

[AnnaWood]

Are any bodies/parts hidden and you have the box in mass properties set to ignore hidden bodies/parts.

Anna Wood
Xeon W3680, Nvidia Quadro 4000, 12 Gb RAM, WD Velociraptor, Dell U3011 Monitor
SW2011 SP1, Windows 7 x64

http://www.solidmuse.com

http://www.phxswug.com

 

[handleman]

Post...Your...Files.

It is much easier for us to be able to see what is happening rather than make wild guesses.

-handleman, CSWP (The new, easy test)

 

[gwubs]

Regarding mass calculation errors, we have seen dramatic INCREASES in assembly mass due to assembly cuts. If you are saying "That's impossible", then you have to believe me, it is. One of our designers here pretty nearly fainted when his weight sensitive trailer assembly "gained" some 2500 lb. while he was doing some assembly cuts late in his design. The only way we got accurate mass readings was to suppress, and unsuppress each assy cut and force a full rebuild. Ctrl+Q alone did not coorect it. All of out part masses were 100% correct. We run an API tool we wrote to analyze all of our assemblies, allowing us to see things like weight and density of parts at a glance. To this day we double check all assemblies with assembly cuts in them, to make sure the assembly mass matches the sum of the parts.

 

[Updraft]

gwubs,

You could make a custom BOM template for the sole purpose of exporting/using it separately in Excel. Customize the template to include the part densities and weights. In Excel add a sumproduct of the weights * quantities to get the total weight. Some of us are not so adept with API. The BOM tables can be shown in an assembly now, not just the drawings.

- - -Updraft

 

[gwubs]

Good point about BOMs Updraft. Running our anlyzing routine is how we generate lists for all our projects anyway. This is done through assembly traversal as VB code running in Excel. So this is not an extra step, we run this on all our models to get our lists. I'll try to attach the Excel file that got it all started for us

 

[gwubs]

Hmmm. That doesn't work, probably doesn't like the German character in the filename. I'll try again