So how are parts “put together”? Well they fasten together, go into each other, become flush with each other, are pressed into each other, are allowed movement in specific directions, are made to touch in a specific way. There are all kinds of ways in which we put parts together, but how do we represent that in SolidWorks? The answer is through geometric constraints called Mates.

Parts within a SolidWorks assembly are constrained to one another through mates which are very similar to geometric sketch relations used in the sketch environment: coincident, concentric, tangent, distance dimension, angular dimension, etc. The most common mates in SolidWorks assemblies are coincident and concentric due to how often things are made to be flush or aligned with one another.

Mates are a command where you can add different mates to different part features such as faces, planes, edges, vertexes, axes, etc. The most robust way to apply mates is by applying them to default reference geometry, such as default planes or axes, that are linked to the design’s datum reference frame (a GD&T term). For more information on Mate Best Practices, see SolidWorks Help: Mate Best Practices linked here.

To apply mates, activate the mate command from the Assembly tab of the CommandManager, click on the features you want to add a mate between, and then verify your mate type. SolidWorks is usually great at knowing what kind of mate you want to add based on what you select so it will usually already be selected.

Another way to add mates more efficiently is through SmartMates which is more automatic. When moving a component from the feature you want to mate, hold down the ALT key on your keyboard and move your cursor to the mating part’s feature. When you release the mouse, you can verify and select the mate you desire if it wasn’t already selected.

Standard mates will be the ones you use most often and are shown by default when you activate the Mates Command. They appear in the Property Manager under the heading “Standard Mates”.

Coincident

The coincident mate is for bringing features, particularly faces/planes, together. When you want two or more faces or planes to be flush or lines up, use this mate. Select the two features you want to line up and coincident should automatically be activated. If needed, you can flip the alignment at the bottom of the Standard Mates section to make the alignment the correct orientation. When you activate different mates, a context toolbar also appears for verifying the mate type and flipping the alignment. This is to reduce mouse movement, so you don’t have to move your cursor all the way to the Property Manager.

Concentric

Concentric centers cylindrical features together: pins to holes, holes to holes, tapered shafts to tapered holes, etc. Concentric is used when the cylindrical feature is not lined up with the default planes of the part model (in terms of GD&T, it isn’t a datum feature).

The Lock Rotation option is for when you are lining up press fit cylindrical features, fasteners, hubs fixed with a set screw, or other features you don’t intend to be free to rotate. You can check the Lock Rotation option to prevent rotation of the mate combination to better match design intent and to give more accurate results in motion studies and analysis. For example, in figure 7.7, the pin is intended to be press fit into the crank.

Like with Coincident, you can flip the alignment of concentric mates as well to ensure the features are oriented appropriately.

Parallel and Perpendicular

Parallel and Perpendicular mates will make planar or cylindrical features parallel or perpendicular as you can imagine. These two mates are very seldom used. Although it is perfectly acceptable to imagine a cylindrical feature perpendicular or parallel to a planar feature, SolidWorks will not allow parallel/perpendicular mates to be applied to planar and cylindrical faces together; you must do two or more planar features or two or more cylindrical features, not mix and match.

Tangent

Tangent mates are used most often for touching planar features to cylindrical features together or for touching eccentric circles together. Some examples are pin/hole combos with lots of clearance and set screw ends onto cylindrical shafts. See the example below where a set screw bottom is being connected to a shaft using a tangent mate.

Distance and Angle

Distance mates and Angle mates are used to specify spaces between two features. In the figure below, you can see .030 inches being applied between two planar faces. The same can be done for angles. Distance and angular mates are popular for moving components (when a limit mate isn’t necessary).