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SmokinPRanch
01-02-2010, 10:11 AM
Hey yall...new guy here. Been spending time reading a lot of past topics and posts. Good stuff.

I've created some 3D solid models with AutoCAD 2000. Been trying to do more designing in 3D to keep a little in practice. I want to explore the mass properties command a little more mainly for experimentation and practice.

Question is....to get the weight of an object, do I multiply the volume by the density of material? Also I notice that the volume and mass are the same on the objects I've inquired...are these values always the same?

Appreciate any info.

Al

Nomand
01-02-2010, 12:42 PM
Question is....to get the weight of an object, do I multiply the volume by the density of material?

In general - yes. But be careful about units of measurement.

SI system: Volume - m3, density - kg/m3, Mass (NOT WEIGHT!!) W=V*d=kg.

Imperial: Volume - in3, density - lb/in3, WEIGHT (NOT MASS) P=V*d=lbs-force.

And about the same volume and mass - meaning you set density of material = 1. This happens only for water in SI system.
Density of water = 1tonn/m3 or 1000kg/m3 or 1kg/liter.

Again - work out your units.

Good luck.

SmokinPRanch
01-02-2010, 01:50 PM
Thank you.

AutoCAD does set the density value to 1 when doing the mass calculations. For now, just a feature I wanted to explore and learn a little about.

Thanks,

Al

ElGuapo
01-02-2010, 02:37 PM
Carefull with the given moments of inertia. Make sure 2D polylines are converted to regions and propery added or substracted.

For calculations with 3d moments of inertia (strength calculations) allways get a feel of what it should be approximately. Then you can estimate wheather AutoCAD is right or if your model is right for that matter.

SmokinPRanch
01-02-2010, 05:37 PM
I'll have to do some studying before I work with the moments of inertia. It is something I've been wanting to learn about. Whenever my designs needed to be analyzed there was always a "calculations guy" to take care of it.

Thanks for the information. It does remind me I have some more studying to do.I'd also like to learn a bit about the basics of FEA so I think MOI would be a good base for learning.

Al

ElGuapo
01-03-2010, 05:02 AM
FYI:

Maybe you'd better start learning how to use Autodesk Inventor (Simulation package) which is basically 3D oriented rather then AutoCAD, however I like the 2D features in AutoCAD better then the Inventor interface, but maybe that's personal because I 'grew up' with AutoCAD. 3D is definitely 'the future'.

Inventor simulation suite has a FEA package, rendering and AutoCAD mechanical inside, and much more, but that's all I use for the moment

In my personal experience Solidworks has a better interface and rendering capabilities then Inventor. The way the interface works is similar. There are some instruction vids on youtube. It's the way I switched from AutoCAD to Inventor/Solidworks.

And again, using FEA without basic knowledge of mechanical (engineering) is like relying only on your battery powered GPS on a small sailboat on your around the world sailing trip.

watglen
02-18-2010, 11:57 PM
yeah, a man's gotta know his limitations.

smaw8
03-20-2010, 09:27 AM
Inventor is a real joy. Like anything else there's a learning hump to get over but if you like that kind of stuff that's no hassle.
Best tutorial I found is TEDCF Publishing:
http://www.trainingtutorial.com/
A bit expensive but very helpfull.
They also have tutorials for Solidworks

Metarinka
04-15-2010, 02:44 PM
+1 on inventor. My company was kind enough to put me through a training class on it. Well worth the time. Once you get a handle on parametric modeling it becomes a lot faster to build something in 3D, than it would be to have to build something in 2d and try to derive properties from it. Very powerful mechanical software.