The SolidWorks Geek

I know last week I mentioned that we were finished with sketch tools, for the time being, but I figured one more couldn’t hurt. I was working on a model for work earlier this week that I had created a few features using Derived Sketches and I thought it would be a great topic to discuss. Unlike when using Convert Entities, Derived Sketches can be moved anywhere on your part and they will still maintain their reference to the parent sketch. As the parent sketch is updated, each derived sketch is updated regardless of it’s location.

Creating a Derived Sketch

For today’s example I am using a model I threw together just to illustrate the function. The actual geometry is not important here, just the process being described. Here we have a cut out on one the surfaces that we would like to replicate elsewhere on the part.

In the FeatureManager, select the sketch that makes up the feature.

Then, while holding down the CTRL key your keyboard, select the face (or plane) where you will be placing the sketch.

After selecting the sketch in the FeatureManager and selecting the destination while holding the CTRL key, select Derived Sketch from the Insert menu.

A new sketch will be created that is derived from the parent. If your expecting some kind of confirmation, you will not see one. The only indication you will see is that a new sketch is shown in the FeatureManager followed by the word ‘derived‘. The new sketch will be created directly over the parent but it will be blue since it is not fully defined.

Using your mouse, drag the derived sketch to the intended location on the part. The derived sketch cannot be modified except for it’s position and orientation using dimensions and relations. In fact, you may notice that every tool in the Sketch tool bar is grayed out, this is because you can not even add any sketch elements to the sketch.

All that is left to do is to create your feature from the derived sketch. For this example, we are going to create another Cut Extrude just like the parent feature.

Modifying the Parent Sketch

The best part about using derived sketches it that, unlike when using Convert Entities, you can add, remove and modify entities in the parent sketch and ALL the child sketches will be updated. Take for example the part we have been working on, this peanut shape sketch was just not what I was looking for. Instead, a regular hole would be better suited for this feature.

I can edit the sketch and delete every entity and add all new entities. I must stress here that I said “edit the sketch” and not delete the sketch, deleting the sketch will break the references to the derived sketches.

Upon leaving the sketch, all of the derived sketches have been updated.

Creating Derived Sketch at Different Heights

Derived sketches do not need to be on the same plane, or elevation, as the parent sketch. In fact, the derived sketches don’t even have to share the same orientation as the parent. If the intended face, or plane, is a different elevation; select the face, just as before, while holding down the CTRL key and select Derived Sketch from the Insert menu.

This time when the derived sketch is created, it is in line with the parent sketch but it is not on the same elevation as the selected face. As before, drag the newly created derived sketch to it’s intended location and apply the necessary constraints.

Do another Cut Extrude, and you have a huge time saver.

Deleting the Parent Sketch

I mentioned earlier about deleting the parent sketch of derived sketches. If you attempt to delete a sketch that has derived sketches, they will not be deleted. Instead that will be “underived“, as the message states, and will discuss that further in the next section. If you attempted to delete the sketch by accident, click No and the command will be canceled.

Underiving a Sketch

There will be times when your derived sketch must step out on its own and become it’s own sketch. Everything was fine when the parent sketch was calling the shots but now it is time to modify a derived sketch independent from it’s parent. Underiving a sketch breaks any relationship to it’s parent sketch and allows you to make modifications to the sketch. In the FeatureManager, right-click the derived sketch and select Underive from the menu.

The word “derived” will no longer follow the sketch name and you may continue to changes to the sketch.

Where Have You Been All My Life?

I bet your thinking of instances in the past where using Derived Sketches would have been extremly helpful. When I first learned about Derived Sketches, I wished I could go back and redo many models but I have since made up for time lost. I am sure your already thinking a ways you can use Derived Sketches on your current project. Have fun with it!