This article will tell you everything you need to know about using external references in SOLIDWORKS, and what you should and shouldn't do!
Introduction
First of all, let's agree on the definition of an external reference.
Definition: External references are created when a part is built directly into an assembly. Using the existing geometry of another part to help create a new part generates an external reference. So if the referenced element changes, the reference that depends on it also changes.
Using external references is a useful practice when the design is going to change a lot. This applies in particular to preliminary projects.
Caution: at a more advanced stage of the design (final design, production), external references must be removed or broken.
I - Not so practical!
Using external references may seem straightforward, but it tends to give rise to a whole host of complications that we could do without!
1. Forget about manufacturing
As indicated in the introduction, the geometry of external references depends on the geometry of other parts. So there are no dimensions to speak of, no tolerances or anything else... which is to say that it would be complicated to start manufacturing such parts!
2. Endless calculation times
Each modification made to the original part will result in the external references that depend on it being updated. If the assembly concerned is fairly large, this can lead to long calculation times.
The presence of external references increases the risk of parts taking a long time to load when they are rebuilt, opened or saved.
Be careful: as well as wasting time, you risk crashing SOLIDWORKS and losing some of your work.
3. Lost or corrupted references
Modifying files will also cause problems: moving, renaming or deleting a file will lead to lost external references.
To illustrate, let's imagine that we create part 1 in assembly A and want to use it in assembly B. Part 1 depends on Assembly A, which is not present in Assembly B. This creates an external reference with no link in assembly B, causing a loss of reference.
As a result, the software will 'run in a vacuum' trying to find the missing references. That's calculation time for nothing!
Once again, you're going to waste a lot of time and risk crashing everything.
4. The vicious circle
When you start working with external references, you very quickly end up with a lot of them and, above all, they all depend on each other. This can lead to cyclical references. SOLIDWORKS may then display error messages or crash.
Please note: the more external references there are, the greater the potential for problems.
5. Time bomb
At the start of the project, there are fewer external references, links are not lost - everything works.
After a few weeks or months, things may be less well managed: references lost, broken, cyclical... Your assembly is very slow, there's a problem.
But you're nearing the end of the project, you're in a hurry, and you need to find the source of the problem. But you have external references everywhere: sketches, functions... It's almost impossible to delete them all.
In CAD, design intent is very important. The work you do in the first few days can avoid problems that will only appear several months later.
To sum up, as you can see, using external references has a snowball effect on design problems.
II - Adopt the right reflexes
Using external references must be a carefully considered design intention.
It is strongly recommended that you work without them, to ensure a robust design. However, if the context requires you to work with them, it's best to learn how to do it properly.
1. Working without external references
Working without relying on external references is advantageous, as it allows a more autonomous design, minimising the risk of complications associated with modifying files. There is also an option to prevent the use of these references, providing an effective means of preventing their use by designers.
In SOLIDWORKS, simply go to the options and uncheck the box for authorising the creation of external references.
2. Working with external references
2.1 Keeping an eye on external references
External references are like children: you have to keep an eye on them! You always need to know where they are and what they depend on. In this way, you can avoid multiple links and the other problems encountered in the previous section.
External references can be viewed in the design tree; a small arrow stuck to the name of an element indicates that it is an external reference. These arrows give an indication of the 'state':
- -> : reference "in context", working correctly
- ->? : reference "out of context", file loading problem
- ->* : reference locked, cannot be modified
- ->X : reference broken
When you move your mouse over an external reference, a link is drawn showing to which part it belongs.
External references can also be accessed by right-clicking on an item and selecting "External references".
2.2. Locking external references
When the model has been completed, it is useful to lock it.
Tip: locking external references reduces loading times when rebuilding assemblies.
When an assembly is locked, this means that the external references will not be updated. To update, simply unlock the assembly and rebuild it.
To lock the external references, use the "External references" command described above.
This gives access to the following dialogue box:
You can unlock your external references at any time.
2.3 Knowing how to work with a skeleton
One of the fairly common practices in designing with external references is to use a skeleton as a basis.
The skeleton is a part which contains no 3D, only sketches. The parts of the assembly refer to this skeleton in order to be placed.
Bear in mind that the skeleton should only be used for positioning your parts, not for dimensioning them.
Conclusion
External references should be used with caution, and only in the preliminary design phase. A design that does not use them will be much more robust and will avoid a good number of problems that could cost you a lot of time.
Further reading
Find out more about external references.