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Assembly Constraints Overview

In the standard workflow of Alibre Design, a combination of parts, sheet metal parts, and even other assemblies can be inserted into an assembly workspace and constrained together to create an assembly design. Assembly constraints are used to correctly position the inserted files with respect to each other in order to limit their movement. For the majority of items in an assembly, all of the movement should be removed unless the items are designed to move or rotate; such as a cam in an engine or a pulley on an axle.

The Quick Constraint and the Standard Constraint are two different assembly tools that will give you the same end result and both of these tools are demonstrated with the Mate and Align assembly constraints.

  • The Quick Constraint tool is context sensitive meaning that the icons in the dialog box change when different geometry is selected.
  • The Standard Constraint tool lets you see what items have been selected to be used in the assembly constraint.
  • The Mate assembly constraint is typically used with planar surfaces but it can also be used with reference geometry. This constraint will orientate the two selected items on the same plane so they are facing in opposite directions to each other.
  • The Align assembly constraint can be used with planar surfaces, cylindrical surfaces, edges, or axes.
  • When Planar surfaces are selected they will be orientated on the same plane so that they are facing in the same direction to each other.
  • When Cylindrical surfaces, edges, or axes are selected it will align the centers of the selected items so they share the same axis.

Constraining the parts:

Mate versus Align

The planar surface of the Valve Spring Seat needs to be mated to the corresponding surface on the Engine Body. If it was incorrectly orientated then the Flip button can be pressed and the Mate constraint will automatically be changed to an Align constraint. This demonstrates the main difference the Mate and the Align assembly constraint.

Reference Geometry

Since the Lifter Spring is a helix there may be no planar or cylindrical surfaces that can be used with the assembly constraints. However, by right clicking on the part and selecting Show Reference Geometry, the planes and axes of the Lifter Spring can be used to constrain it to other parts.


Regardless if the Quick Constraint or the Standard Constraint is used, the end results will be the same. In this example, the Align assembly constraint is demonstrated with the reference geometry of the Lifter Spring (the X-Axis) and the cylindrical shaft of the Lifter Valve.


Making a linear or circular pattern of individual parts or entire subassemblies allows you to only have to apply the assembly constraints once. In the example below, many different assembly constraints were used to position a variety of parts and a subassembly to the Engine Body. Instead of inserting the same parts into the assembly and adding additional assembly constraints, the parts were patterned with the Linear Pattern tool. Since they are a pattern, their distance is controlled in the Linear Part/Subassembly dialog box. Making patterns of can eliminate a lot of redundant work.