how to calculate where to fit lifting lugs with CAD

hi all

I have ordered engineering design of a very large tower crane tie, it spans over 8m from building to tower crane.

i would like lifting lugs on it. the design engineer works in 2d so he doesn't know how to calculate where exactly to put the lugs (in every other way this engineer is the best there is in tower cranes)

i suggested i could draw it for him in 3d and do mass properties command so that he has the centre of gravity.

would this be the best way to proceed or is there a better way?

Hopefully this will get moved to the 3D section where it belongs. Much better exposure when in the right section.

So you don't actually need help creating the 3D model you just want to know where to locate the lifting lugs? What exactly is being lifted?

For the record, AutoCAD can't "calculate" this type of request. I don't even think it will give you center of gravity from MASSPROP either, unless I'm mistaken. Isn't this more for programs like Inventor and Solidworks?

If I understand the problem correctly you do not need a 3D model. The XY location of the center of gravity is what is needed. It's Z coordinate does not affect the tipping moment when the load is lifted straight up.

You can calculate the CG of a system by creating solid 3D boxes that have volumes equal to the weight of the various components of the system. Since, I believe, AutoCAD does not allow you to assign a density to a solid you have to use the object's volume to represent its weight. The centers of the boxes should be positioned at the CG location for each component. Select all the boxes and then give massprop command to determine the CG of the collection of boxes.

If you don't know the CG location of each object in the system then building a 3D solid model would be necessary. If all the components have the same material then you can directly use massprop. If some components are of a different material then they must be scaled by the ratio of its density to the density of the reference material. For example, an aluminum (density ~ 0.1 lb/in^3) component would need a volume about 3 times larger than if it were made of steel (density ~ 0.3 lb/in^3).

~Lee

ok ive confirmed with an old workmate and 3d guy who does this all the time

i draw the members in 3d, as they are all steel the density does not matter.

i type in massproperties (or massprop) and there in xyz coordinates is my centre of gravity.

from there its a bit of mathematics to work out where to put lugs.

cheers all for your help

For the record, AutoCAD can't "calculate" this type of request. I don't even think it will give you center of gravity from MASSPROP either, unless I'm mistaken. Isn't this more for programs like Inventor and Solidworks?

Centroid is Center of Gravity, I suppose?

Centroid is Center of Gravity, I suppose?

centroid

ˈsɛntrɔɪd/

nounMathematics

noun: centroid; plural noun: centroids

• the centre of mass of a geometric object of uniform density.
   
   
   
   
  

I stand corrected. Thanks mvrcad.

-TZ

centroid

ˈsɛntrɔɪd/

nounMathematics

 

noun: centroid; plural noun: centroids

 

• the centre of mass of a geometric object of uniform density.
   
   
   
   
  

The centroid is the geometric center of geometry, the center of mass is the mass center of a physical object. If the objec's material is of uniform density then the center of mass and centroid are at the same location. If that object is in a uniform gravitational field then its center of gravity is the same as the center of mass and centroid.

yes, correct, i shouldn't have relied on google

my wife studying her degree in information reliability would be peeved if she knew i quoted google.