You want the changes you make in your CAD assemblies to be effortless. I have found that is rarely the case. When you replace a part in an assembly a variety of things goes wrong. The feature tree lights up red with broken mates and bad references everywhere. The simple change has turned complex. Again. Now you have to go through each of the broken mates and reattach the parts. Time wasted.
You can avoid this hassle by using plane mates in your assemblies. These mates are more robust because their references do not rely on specific surfaces. Surfaces which are constantly changing during the modeling process.
If the standard Front, Top, and Right planes are not a good choice in your parts then you should create some reference planes and tuck them away in a folder near the top of your feature tree. Planes near the top of the feature tree will be easy to select when you are adding or replacing component parts in your assemblies.
Named mating planes make it super easy to change component parts in assemblies.
The planes shown in the image above belong to a gearbox. They would make it really easy for you to change the standard motor in an assembly with a special motor on customer request. Simply mate the front mounting face of your motor to the “motor mounting face” plane and the Top and Right planes in your motor part to their respective mating planes. Done.
Setting up all of your parts in this manner makes it trivial when working with standard components. If every motor component part has mating planes that match up to the gearbox mating planes shown above then you can simply use your CAD software's “replace component” command. Just like working with Legos. Now you can easily customize your standard assemblies without ever breaking mates again. No more wasting time when a customer needs something a little different from the standard assemblies you painstakingly created. Which is almost every order in my experience.
Your assemblies will generally work better and break less if you start using planes for common mating situations. Let's say you have a hardware file that contains all of your bolt configurations. You use those bolts in thousands of different assemblies. Mating these bolts in place using the bottom of the head and the cylindrical face of the shank. One day it becomes apparent that you need a new feature in these bolts. A groove cut into the shank of every bolt to show where the threading stops. You open up the bolt file and adjust the sketches to include a small groove at the thread end.
ALL of your assemblies break. Well maybe not all, but all the ones that use bolts anyways. Adding that groove broke every reference to the original bolt shank surface. Because now you have multiple surfaces on the bolt shank and the software doesn’t know which one to automatically select.
So you have to go through and select them all again. Thousands of times. Or you could have set up your original bolt file with a couple of reference features.
A central axis along the bolt length.
A plane under the head of the bolt where it contacts the surface.
This simple difference means that no specific geometry of the bolt file is used for mating hardware in place. You can edit every surface of the bolt and even change how the basic modeling is constructed without ever worrying about causing errors. This will continue as long as the reference features were carefully chosen to represent the basic locating features of the bolt. You can use this method with all parts but a bolt was a simple example for showing the concept here.
Mating to surfaces can cause major problems in the future if the basic geometry changes.
Mating to these reference features instead creates less chance for future problems.
Working with reference features takes slightly more time up front than just clicking surfaces. However, you will save a lot more time in the future by not having to go back and fix old assemblies when something changes in a commonly used part.