Creo Parametric Tip: Settings that Change How Assembly Constraints are Applied by Default

By Natasha Reaves

When the assembly constraint type is set to Automatic, Creo creates constraints based on what geometry you choose and their relative locations and values of thresholds set in the configuration settings. For example, when you mate two surfaces, their original position with respect to each other just before the final geometry selection determines whether the constraint type assigned is Normal, Coincident, Distance, or Angle.

There are several configuration settings that establish a threshold for how Creo selects each constraint. For example, if the surfaces are coincident within one epsilon but too far apart to be within another epsilon, then Creo selects Distance. If you know what these epsilons are, you can reposition the component (either by using the 3D Dragger or <CTRL> + <ALT> + mouse) prior to selecting geometry so that Creo automatically selects the constraints you want.

The configuration option  auto_constr_always_use_offset  controls whether auto constraints should create offsets.

By setting the option auto_constr_always_use_offset  to yes ...              

Distance, Angle, or Normal will be the default constraint type for the following reference pairs:

• Planes
• Linear edges/ Datum Axis
• Planes combined with Linear edges

By setting the option auto_constr_always_use_offset  to no*…

 - Creo will suggest a constraint type based on the existing component position and orientation:

• Coincident
• Distance
• Angle
• Normal

- Auto constraints snaps align or mate if surfaces are within tolerance

- Orientation tolerance is set with the options:

• comp_normal_offset_eps
• auto_constr_offset_tolerance

By setting the option auto_constr_always_use_offset  to never ...

Coincident will be the default constraint type for the following reference pairs:

• Planes
• Linear edges/ Datum Axis
• Planes combined with Linear edges

Additional information about the customizing Creo and how customizing enables you to follow a more efficient workflow can be found in our Introduction to Solid Modeling course.

About the Author

Technical Training Engineer<br><br>Natasha joined the company in 2000 and has extensive experience sharing her CAD expertise through delivering webcasts, contributing to blog posts, and leading training classes. She trains end-users with all skill levels on Creo Parametric and CATIA, and she collaborates closely with the company’s technical writers on courseware development. Before joining Rand Worldwide, Natasha served as a mechanic in the U.S. Army National Guard and worked as a mechanical designer for a multinational telecommunications and data networking equipment manufacturer. She has a bachelor’s and a master’s degree in Mechanical Engineering, and she holds certification from Dassault Systèmes as a CATIA V5 Expert Mechanical Designer and Certified Surface Design Associate.

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