Mates in Onshape are different than mates in old CAD systems. Many assemblies require only one Onshape Mate between any two instances, as the movement (degrees of freedom) between those two instances is embedded in the Mate. Mates contain their own coordinate systems, so you can use one Mate to define the degrees of freedom between two entities. At the time of placing a mate between two entities, Onshape offers points on each entity to which to align with the mate's coordinate system. The suggested locations are based on the underlying geometry of the part and changing the geometry will change the location of the mate. This can be undesirable in certain situations, but you can also:

  • Add an explicit Mate connector to an entity exactly where you want it if the geometry does not already allow an implicit Mate connector while creating a mate. For more information, see Mate Connector.
  • Insert a layout or reference sketch in an Assembly to use for aligning Mate connectors.
  • Use more than one mate if necessary.

For additional Learning center resources, follow the technical briefing articles here: Mating Basics (Onshape account required) and Advanced Mating Techniques (Onshape account required).