AutoCAD Moment of Inertia Calculator

[Noor]

Hello everyone,

I'm looking for a good (low-cost... prefereably no-cost) moment of inertia calculator routine for autocad. Does anyone know of one?

 

[vzeos]

Searched Autocad Help for "moment of inertia". You should get some information about the MASSPROP command. This may be what you are looking for.

 

[IFRs]

Make the profile a closed polyline (use the PLine command or PEdit and Join) then convert it to a Region with the Region command (pick the PLine). Then use the MassProp command and pick the region. Press F2 to see the results.

 

[Noor]

Thanks for your help guys!

I'm working with 2D drawings, and the only way I was able to get moments of inertia was to make a 3D model from them, and do massprops...

however, now that IFRs showed me the missing "region" step, I'm all set!

THANKS!!!

 

[Kwan]

I make the section and type region, then select the section. pline isn't required.

 

[GregLocock]

Sounds to me like you'd better check the result. It would be a mighty clever algorithm that can work out 3d properties from a typical 2d drawing (there are some programs for which this might be possible, but I don't think Autocad is one of them)

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[IFRs]

The section properties that AutoCAD's MassProp command gives you are the area, bounding box, centroid, product of inertia, radii of gyration and moments of inertia about two axis. It does not need to be a 3D object. Using region without a closed polyline does give the same results. I always use closed polygons out of general habit and previous versions that required them. I also wrote some software that needed closed polylines.

 

[mrMikee]

Note that when you use the drop down menus to get properties you start at the "Tools" menu, select "Inquiry", then "Region/Mass Properties." This still ends up at the MASSPROP command but the wording "Region/Mass" does seem to differentiate between 2D (region) and 3D (mass) functions, which in my opinion is more technically correct.

Another handy thing to know is how to subtract one region from another for when you have a hollow section. This is found in the Modify menu. I generally cross hatch the final section to check out if I did it right.

Modify->Regions->Subtract

Regards,
-Mike