 # Volume Moments Of Inertia

Hello

I need to enter the mass moments of inertia of my milling spindle into my robot’s tool settings.

I calculated the Volume moments of inertia based on the 3D model of my spindle in Rhino but I was wondering how I can factor in from here for the mass of it.

Thank you

Multiply by density?

This is, I think, most easily done using unit analysis. I will use SI units, but you can substitute feet or furlongs at your leisure.

Volume moment of inertia has units `[m^5]`, which you can think of as `[m^3*m^2]`, the first one for the volume, the second for the rest.

Mass moment of inertial has units `[kg*m^2]`, the kg for the mass, the second is the same as the units above (`[m^2]`), So you need to go from `[m^3]` to `[kg]`. As @davidcockey already mentioned, multiplying by the density `[kg*m^-3]` (i.e `[kg/m^3]`) will do just that.

Menno thank you so much. This is exactly my sticking point. The units.
So if I am working on a Rhino scene and my units setting is in millimeters then that means that the results that I get in mass analysis for volume moments of inertia are also in millimeters^5 or are in meters^5? Do I need to set my scene units in meters first? I need the results in kg*m^2 as you pointed out.
Thank you.

Konstantinos Papalexiou

Neoset Designs
63 Flushing Ave
Brooklyn Navy Yard
Cel: 3476619001

URL: www.neosetdesigns.com
Instagram: www.instagram.com/neoset_designs

Results from mass analysis commands are in the same units as shown in the properties screen and used elsewhere in Rhino.

Set the units in Rhino to meters and yes to scale. Calculate the moments, etc. Then multiply by density in kilograms per cubic meter.

Thank you David.

Konstantinos Papalexiou

Neoset Designs
63 Flushing Ave
Brooklyn Navy Yard
Cel: 3476619001

URL: www.neosetdesigns.com
Instagram: www.instagram.com/neoset_designs

hello,