About Mechanical Junctions

The mechanical junction is a collection of mechanical interfaces. You can use existing mechanical interfaces in the 3D shape or create them on the fly. Along with the functional surfaces, mechanical junctions are essential features required to generate and update the tolerancing schema of an authored 3D shape.

This page discusses:

Types of Mechanical Junction

The type of the mechanical junction specifies its role in setting and maintaining the position of a feature during assembly with respect to the mechanical interfaces.

Following are the types of mechanical junction based on its role during assembly:

  • Main Part: The mechanical junction that sets and maintains the 3D part in position as a component in an assembly. By default, the first mechanical junction is a main part mechanical junction.
  • Main Block: The mechanical junction that sets and maintains in position, or contributes to set and maintain the 3D parts in position as a sub-assembly component in an assembly.
  • Auxiliary: The mechanical junction that sets and maintains in position, or contributes to set and maintain other 3D parts in position as a component in an assembly. By default, the mechanical junction created after the first one is an auxiliary mechanical junction.
Roller Assembly

Main Block Mechanical Junction

Auxiliary Mechanical Junction (1)

Auxiliary Mechanical Junction (2)

Main Part Mechanical Junction (1)

Main Part Mechanical Junction (2)

Role of Mechanical Interfaces in Mechanical Junctions

To create a mechanical junction, the mechanical interface needs to be defined. After specifying the type of the mechanical junction for the feature, the positioning of that feature is decided based on its mechanical interfaces. This ensures a perfect engineering connection in the later stage of design.

  • The mechanical interfaces of the main part mechanical junction are specified according to its positioning over main block or auxiliary mechanical junction.
  • The mechanical interfaces of the main block mechanical junction are specified according to the positioning of the main part and other main block required over it. It is also defined according to the position of the main block over the auxiliary or other main block mechanical junction.
  • The mechanical interfaces of the auxiliary mechanical junction are specified according to the positioning of main part and the main block mechanical junctions associated with it.

The mechanical interfaces specified for the mechanical junction are displayed in the Mechanical Junction dialog box, under Mechanical Interface Component(s).

Icon Description


Primary entity is not specified for corresponding mechanical interface


Primary entity is specified for corresponding mechanical interface


Secondary entity is not specified for corresponding mechanical interface


Secondary entity is specified for corresponding mechanical interface


Tertiary entity is not specified for corresponding mechanical interface


Tertiary entity is specified for corresponding mechanical interface


Set in position entity is not specified for corresponding mechanical interface


Set in position entity is specified for corresponding mechanical interface

When you specify the surfaces for the mechanical interfaces, the pointer appears with a dedicated colored surface and an axis system representation. By default, while creating or editing mechanical interfaces, the pointer appears with a primary entity surface icon. You can click in the work area to switch to the next surface entity to define the set in position surfaces. Further click in the work area finishes the creation of mechanical interface.

When you are working in the Mechanical Junction dialog box, and you click in the work area or under Positioning and Maintaining Geometry, the loop of surface entity selection continues.