Concentric Mates
We know that each unconstrained body in space has six degrees of freedom (DOF): three translations and three rotations about X, Y and Z axes. Each mate removes a certain number of DOFs from the system. The table below shows some of the mates in SOLIDWORKS and how many DOFs that they restrict. Mate Type Translation DOF Removed Rotational DOF Removed Total DOF Removed Hinge Mate 3 2 5 Concentric (2 cylinders) 2 2 4 Concentrix (2 spheres) 3 0 3 Lock Mate 3 3 6 Universal Mate 3 1 3 Screw Mate 2 2 (+1) 5 Point to point 3 0 3 What Are Redundancies? Redundancies are when multiple mates remove the same DOF on a part. For example, if we create a pin joint we most likely use a concentric mate between the cylindrical faces of the pin and the hole and a coincident mate between the flat…
Working with downloaded or imported models can create a situation where multiple pairs of holes cannot be mated concentric although there is no problem fitting manufactured components. SOLIDWORKS 2018 misaligned concentric mates option can account for this small difference in hole distances. When the option ‘Tools > Options > System Options > Assemblies > Allow creation of misaligned mates‘ is enabled: A conflict in concentric mates allows using a misalignment option as shown in the screenshot below: In the PropertyManager for the concentric mate, offset can be applied to the first or second set of holes, or equally split between two sets. Maximum deviation can be set when the option ‘Use Document Property’ is disabled. Misaligned mates are shown in a separate mates folder.
Working with assemblies we sometimes have holes that are slightly misaligned, especially when working with imported parts from a supplier. Even though they are still within spec and will work for the intended use, we get the Over Defined ketchup and mustard in our feature tree. But now with SOLIDWORKS 2018 we have this new option under the concentric mate called “Misalignment”. The SOLIDWORKS Concentric Mate Misalignment option provides us with the ability to still add the mate, but choose which hole in the part[s] to be misaligned or even have the concentric mates symmetrical (meaning both will be offset the same distance). This option also gives us the opportunity to define the maximum allowable deviation. For those holes which cannot have any deviation, don’t worry this option can be disabled through the System Options hiding the option from the PropertyManager.
Starting in SOLIDWORKS 2014, you have the ability to lock rotation of concentric mates. This can help avoid additional mates required if you didn’t want the components to rotate. Review Chris’ blog post for a quick tutorial of this functionality. How to quickly tell if a concentric mate rotation has been locked In order to see if a concentric mate rotation has been locked, simply review the mate icon for the component. A regular concentric icon will show two concentric circles. The locked rotation icon will have a solid circle on the inside. The following images use Breadcrumbs and D-key for easier viewing. What if a component is already fully defined? If a component is already fully defined, trying to lock one of its concentric mates will fail and provide a message that rotation is already locked for all concentric mates. As you can see in FIGURE 3, the three concentric…