How to Use Assembly Mass Properties in BricsCAD Mechanical

Quick answer: An assembly can consist of multiple parts made from different materials. To correctly compute mass, centre of gravity (centroid), and inertia across such assemblies, BricsCAD supports individual densities per component, defined via the Material property in the Mechanical Browser, confirming and expanding the Density note covered on this hub’s mechanical block properties page. By default, a component inherits the density of the assembly it was inserted into or formed from.

Setting the Mass Units

1. Open the Settings dialog.
2. Expand Property units under Drawing / Drafting / Drawing units.
3. Tick Format mass properties to enable proper unit formatting for mass values.
4. Select the Mass units field.
5. Click Browse.
6. Specify the units you want in the MASSUNITS dialog.

The Mass units setting only affects mass values themselves, other mass properties (density, moments of inertia) always format in SI units for a metric drawing, or imperial units for an imperial drawing, regardless of this setting.

7. Specify the precision you want in the Mass precision field.
8. Close the Settings dialog.

Computing the Mass Properties

Use BMMASSPROP to compute mass properties for the entire model, or just a selection of 3D solids and/or subcomponents. It reports mass, volume, centroid, moments of inertia, products of inertia, radii of gyration, principal moments, and X-Y-Z directions about the centroid, all in the Command line.

Optionally align the User Coordinate System with the inertia axes, placing the component’s centre of mass (or centroid) at the UCS origin, useful for investigating how a product behaves under gravity.

Frequently Asked Questions

What density does a mechanical component use if I haven’t set one explicitly? It inherits the density of the assembly it was inserted into or formed from.

Does changing the Mass units setting affect how density or moments of inertia display too? No, only mass values themselves are affected; density and moments of inertia always use SI units (metric) or imperial units (imperial), regardless of the Mass units setting.

Can I compute mass properties for just part of my model, rather than the whole assembly? Yes, select the specific 3D solids and/or subcomponents you want before running BMMASSPROP.

Why would I align the UCS with a component’s inertia axes? It places the centre of mass or centroid at the UCS origin, useful for investigating the product’s behaviour under gravity.