The Onshape Mass properties tool is available in Part Studio and Assemblies for parts and assemblies. Find the Mass properties tool in the bottom right corner of the interface (desktop, shown below in a screenshot) or on the main toolbar (iOS and Android), the scales icon, when you have parts selected.
You can also use this tool to override properties and supply your own values for mass.
Properties are additive: for each additional part you select, its properties are added to the calculations in the dialog (desktop) or flyout (iOS and Android). When you apply materials to parts, the density of the material is used in the calculations in the Mass properties dialog/flyout. If a part has no material assigned, no figure for that part is used in the calculation (and a note is displayed in the dialog/flyout to that effect).
Results of mass property calculations are approximate. The calculation of the properties may vary in accuracy, depending on the complexity of the geometry.
Enabling Show calculation variance displays the value and the difference between the lower and upper bound of the calculated value. If Show calculation variance is not enabled, the computed value without the bounds is displayed. The computations of the values are not affected by the state of the Show calculation variance checkbox.
Apply Materials to parts through the context menu on a part in the Parts list (or the graphics area).
Mass Properties Tool: Desktop
Video example
Video transcript
The Mass properties tool allows you to view and override Mass, Volume, Surface area, Center of Mass, and Inertia for Parts in Part Studios and Assemblies. First, Parts must have a material assigned to them. Right-click the Part and select Edit Material. Then assign a pre-made material from the Library or select Custom and enter values. The density of the material is used in the Mass properties calculations. Next, click the Mass properties tool at the bottom right corner. Select the parts to include in the calculations. If a part has no material assigned, it is not used in the calculations and displays red (for example, the Spindle here). Properties are additive: each additional part selected adds to the calculations in the dialog. Click the red x to exit the Mass properties dialog.
Mass properties is also available from Assemblies. Click the Mass properties tool and then select the parts to make up the calculations. Click the red x to exit the dialog.
Steps
- To access the Mass Properties dialog, select a part in the Parts list. (You can also open the dialog first and select after.)
- Click the Mass Properties tool icon
in the bottom right corner of the interface.
- If you wish to override calculations and enter your own values for Mass, Center of mass, and Mass moments of inertia, place a check in the Override box for the property you wish to override and enter the desired value. Appropriate recalculations are made once a new value is entered.
Mass properties override checkbox on browser, above
Mass properties override checkbox on iOS, above
For any intersecting parts, the properties are calculated for each individual whole part and added together.
Using values
You have the ability to use the information displayed to enter values elsewhere in the system, for example, as a dimension.
- With the Mass properties dialog expanded, click the value to view and highlight the max precision, click again to toggle the view to value with default decimal place setting; use shortcut keys to copy to clipboard.
- The Mass Properties dialog provides the following information, presented from top down as shown in the tool:
- A list of selected parts - Hover over a part in the list and a small red x appears beside it. Use this x to remove the part and it’s properties from the dialog and calculations. Alternately, you can click the selected part in the Parts lists to deselect it.
- Select a mate connector (optional) to calculate the Moments of Inertia more accurately (instead of to the common center of mass of the selected parts (as described below):
- Mass of all parts that have a material applied
- Volume of all selected parts
- Surface area of all selected parts
- Center of mass of all parts that have a material applied
- Moments of inertia - With respect to the center of mass of the selected parts (not the Part Studio origin) and reported using the densities of the materials assigned to the selected parts. Any selected parts without materials assigned are omitted from the calculation. If no materials are assigned to any selected parts, no calculation is made.
Mass Properties Tool: iOS
Mass Properties tool shown in Part Studio toolbar on iOS application.
Mass Properties tool shown in Assemblies toolbar on iOS application.
Steps
- To use the Mass properties tool; either select the tool and then select the part(s) OR select the part(s) first and then the tool.
- You are able to select multiple parts at a time.
- Parts may be selected in both the graphics area and the Feature list.
The Mass properties dialog provides the following information, presented from top down as shown in the dialog.
The information is presented in the default units that you have set for your document. The image above is displaying mass property information in terms of inches (the default unit for this document).
To change the default units for your document, tap the Document menu icon the upper left, select
Units, and select desired length, angle, and mass units.
- Selected entities field - tap to view the list of selected entities. Swipe left on an entity in the list to reveal a delete option. Deleting an entity from the list will remove it from the dialog and calculations.
- Mass of all selected entities.
- Volume of all selected entities.
- Surface area of all selected entities.
- Center of mass.
- Moments of inertia - with respect to the common centroid of the selected parts (not the Part Studio origin) and reported assuming density of 1 in current document unit (mass per unit volume, for example: 1 lb/in 3).
- If you select more than one part at a time, the combined properties of the parts are calculated.
- Any intersecting parts have the properties of each individual whole part calculated and added together.
Mass Properties Tool: Android
Mass Properties tool shown in Part Studios toolbar on Android application.
Mass Properties tool shown in Assemblies toolbar on Android application.
Steps
- To use the Mass properties tool; either select the tool and then select the part(s) OR select the part(s) first and then the tool.
- You can select multiple parts at a time.
- Parts may be selected in both the graphics area and the Feature list.
The Mass properties dialog provides the following information, presented from top down as shown in the dialog.
The information is presented in the default units that you have set for your document. The image above is displaying mass property information in terms of inches (the default unit for this document).
To change the default units for your document, tap the Document menu icon the upper left, select
Units, and select desired length, angle, and mass units.
- Selected entities field - Tap to view the list of selected entities. Tap on Remove (X) to delete an entity. Deleting an entity from the list will remove it from the dialog and calculations.
- Mass of all selected entities.
- Volume of all selected entities.
- Surface area of all selected entities.
- Center of mass.
- Moments of inertia - with respect to the common centroid of the selected parts (not the Part Studio origin) and reported assuming density of 1 in current document unit (mass per unit volume, for example: 1 lb/in 3).
- If you select more than one part at a time, the combined properties of the parts are calculated.
- Any intersecting parts have the properties of each individual whole part calculated and added together.