Weights and Center of Gravity

[cadnutcase]

For the first time I need to use the weights and center of gravity features in Solidworks. My particular application the weights don't have to be perfect and the center of gravity just needs to be pretty close.

If I assign weights to each indvidual part and I have material set right in my weldment assembly, can I trust the weight that comes out of Solidworks in the master assembly.

I did a quick hand calculation and came up with about in 8% differnce, where solidworks was actually a little higher (this is good for me)

The center of gravity was about where I expected to be.

I quess the question is can I trust it?
My assemblies right now are pretty simple, but they won't be in the future. And I am actually moving lifting points based on the center of gravity.

Cadnutcase
SW 2006

 

[btcoutermash]

We have trusted it and it's served us well. My understanding however is that it is measured from the planes in your assembly file, so care must be taken when you decide the placement of the first part used to build the assy from.

 

[ctopher]

I always create my part the way they will be machined with the origin at center of the mounting surface. The CG will base off the origin, I have a detailed material database in SW/CW and all parts are assigned the correct materials. These designs were for major military/aerospace programs. The weights and CG were 100% correct. They were checked by engineers and against real parts/assy's. So, to answer your question, you will get out what you put in.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 05
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

 

[cadnutcase]

Thanks Guys that is what I needed to know.
I was reviewing my model and there were several places that I cheated on a couple of small things, and I think that is where my 8% differnce is coming out.

 

[TheTick]

You don't assign weight to a part. You assign a density, either by material properties or by document properties. If the material density is correct, weight and CG take care of themselves.

Accurate enough to bet your job on.

 

[Beggar]

It seems to me that you've answered it yourself.

If your hand validation is within 8% (and conservative, to boot) and the CG is about where you know it should be, you should feel pretty confident in your results.

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[cadnutcase]

Yeah I feel comfortable, just looking for a 2nd opinion.
So far I have built 2 jobs in Solidworks, so far less errors and problems that I had in 2D autoCAD.

Thetick,
I can overide and assign mass properties to my individual parts. Is this not a good thing?

 

[Beggar]

It's fine just so long as

A) You really know the weight, and
B) You know the part isn't going to change.

It's kind of silly though; why would you not just provide the density and allow the program to do its thing?

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[cadnutcase]

We do alot of skid mounted equipment.
I don't want to draw compressors or chillers or valves down to every last nut and bolt. I would be here forever.

cadnutcase

 

[Mindnumb]

I have also done a lot of skid based stuff, and find SW to be accurate as long as you dont cheat to much... typically problem would be intreference, take care to do a interference check.... its very dangerous not to do it, and it takes no time at all.

 

[cadnutcase]

Mindnumb,

How do you like the piping feature? I think it is a little tough to work with, but still good.

 

[Mindnumb]

I love it for the most part, but performance has been deterioating for every new sw version, so im kind of longing back to 2001+ version, but it had a lot of quirks...

with the kind of work i am doing, piping has been very efficient. No way I would be able to make 1000+ parts assembly in 10 hours without it... if your doing pipes, its a must have.