Functional Datums

So, in this section of the guide, we’re going to break down the difference between regular datums and functional datums in Drafter. Essentially, a standard datum is chosen based on how the part is mounted or how it’s expected to be referenced in the real world. You pick these datums in a structured order, like A, B, and C, based on how critical they are and how many degrees of freedom they can constrain. The goal in Drafter is to lock down at least 5 out of the 6 possible degrees of freedom for your part, though you can constrain all 6 if needed.

Now, functional datums are a little different. They’re not about constraining the part’s movement. Instead, they act purely as reference or measurement points for specific features. So if you need extra datums beyond those main constraining ones, you can create as many functional datums as you like in Drafter.

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Learn More about Datums in Drafter

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Creating Functional Datums

Creating standard datums in Drafter

In the actual Drafter workflow, you’ll be guided to select your primary datum A first. Once you’ve chosen that initial datum, often a regular surface or mounting plane, you’ll notice that you’ve typically constrained about three degrees of freedom right away.

From there, you’ll proceed to select additional datums until you’ve locked down at least five of the six possible degrees of freedom. After you’ve reached that point, any additional datums you add, unless they specifically lock that final sixth degree, will generally be considered functional datums. These serve purely as extra reference or measuring points rather than constraints.

Adding Functional Datums

Now, let’s talk about how to add a functional datum. After you’ve constrained at least five degrees of freedom, so once you’ve got your primary datums set up, you’ll notice a button labeled “Add Datum.” By clicking this “Add Datum” button, you’ll have the option to introduce a new datum, let’s say a datum D, that doesn’t necessarily constrain more critical degrees of freedom.

You’ll see that this newly added functional datum appears in the side panel, slightly indented under your main datums A, B, and C. This indicates that datum D is a functional reference that is essentially tied back to your primary datums but is there for measurement or feature-specific purposes rather than for constraint.

How to reference functional datums to one another

Now that you’ve created a couple of functional datums, the next step is to organize them so that some of them can refer back to each other. Here’s how you do that: First, you select the highest-level or highest-priority functional datum you want to use as the “parent”; let’s say datum E in this example. You’ll hold down the Shift key and select that datum first.

Then, while still holding Shift, you select the other functional datums that you want to reference back to that first one. Once they’re all highlighted, you just right-click and choose the option to “Create a Functional Group.” After that, you’ll see that all those referenced datums are neatly indented under the first one, indicating they form a functional hierarchy.

When done adding datums and creating functional datums, select “Continue” top proceed to critical feature selection.

Referencing critical features back to functional datums

So now that you’ve established your functional datums and linked them to each other, the final piece of functionality is associating specific critical features with those functional datums. Once you’ve moved past the datum selection step and you’re working in the critical features step, it’s straightforward. You can Shift-select any critical feature that you want to link and then also select the functional datum you want it to reference.

After you have them both selected, just right-click, and you’ll see an option to “Create a Functional Group” and have that critical feature reference back to the functional datum. Once you do that, the feature will be associated with that functional datum as its reference point.

Functional Datums in your Drawing

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And finally, let’s talk about how these functional datums will appear in your 2D drawing output. As a result of all the selections you’ve made, you’ll see that these functional datums are represented in the drawing in a way that references back to your original mounting datums, those that actually constrained the degrees of freedom. You’ll also see any relationships you set up, such as a critical feature that’s tied to a specific functional datum, clearly indicated in the datum reference frame. In other words, you’ll see a neat chain of references that show how each functional datum and each critical feature ties back to the primary datums you started with.