Say you want to build a cabinet. You go to Home Depot, buy the wood and buy the tools. Then you go home and realize halfway through, you don’t have a hammer. What do you do? You could try using the wrench as a hammer, but that won’t work well. What if your only option was to dismantle everything you’ve accomplished and start over?
For CAD designers, a missing datum can be like that missing hammer. You need it, just like you need all other types of datums, to build your model. And if you don’t have it, you’re faced with some difficult choices.
Datums 101 and the make-datum command. Whether they are datum planes, points, axes, or coordinate systems, datums make up the indispensable reference geometry upon which all geometry features are “anchored” to the CAD model workspace. Pro/ENGINEER is known for its robust selection of reference geometry, and through the years functionality has been added to improve not just the repertoire of reference geometry, but the ease with which it can be used.
With early releases of Pro/ENGINEER, you benefited from using make-datums. This function lets you create new datums even after you have started designing a new feature without having to cancel out of the feature’s definition.
Historically, you would have defined your reference geometry — datum planes, for example — before starting to sketch a new feature. But once the new feature is underway, you might decide you need a new datum plane or some other construction item to accurately define the feature you’re creating. You might want to define a cut on a surface, for instance, and want to control the depth of the cut based on an offset to a different surface, but you wouldn’t have a datum plane in place to act as the reference.
Without the make-datum feature, you would likely have had to back out of the feature, define the new datum plane for the cut, and then re-do the feature from start. With make-datum, you define the new datum plane on-the-fly, without having to back out of the feature. This saves many extra keystrokes and feature tree clutter as the models became more complex.
Fast-forward to Pro/ENGINEER Wildfire. The construction datum concept has continued to evolve through Pro/ENGINEER Wildfire 1.0 and 2.0.
“During that time we made a number of improvements,” says Netesh Gohil, director of product management at PTC. “In the beginning, make-datum only worked for datum planes, and many customer requirements focused on adding other datums, like datum points, axes, and coordinate systems.” Gohil explains that with make-datum, the datums created by the function didn’t show up in the model tree, so if one designer handed a model off to another designer, the new person wouldn’t be able to understand the original design intent. Another requirement was to have a mechanism to display a make datum and reuse it for another feature’s creation.
“With Pro/ENGINEER Wildfire, we introduced asynchronous datum creation which provided a mechanism for grouping the datums with their features on the model tree. And we also replaced the make-datum command with a toolbar that lets you create new datums without having to leave the screen.”
The grouping function has some advantages. For instance, you can see any datums that have been created for a particular feature, just by opening the group node. Also, you can go into the group node, access the datum definition, and redefine it — something that enhances design flexibility. But the groupings have drawbacks, according to Gohil. For one, they add clutter to the model tree by adding group nodes for every feature using construction datums, an important user-friendliness issue in parts with a large number of features. And for another, they slow down the time it takes to generate a feature pattern — to replicate screw holes in a part, for instance, by using a group pattern rather than a feature pattern.
Pro/ENGINEER Wildfire 3.0 and embedded datums. With Pro/ENGINEER Wildfire 3.0 the construction datum concept comes to fruition with embedded datums.
Now, embedded datums work for the majority of features — before, they were mostly applied only to sketch-based features such as extrudes, revolves, and sweeps.
“Now, I can place a hole on a spherical surface,” says Gohil. “I just create a datum point on the surface, dimension it, and then place the hole on the point. If I double-click on the hole feature, I’ll see all the dimensions of the hole and all the embedded datums used to build the feature. In this case, I see both the hole and datum point’s dimensions.”
With embedded datums group node disappears from the model tree. So to get to the datum definitions you simply click on the on-screen feature itself. This cleans up the model tree and saves keystrokes, and it reduces the time it takes to generate patterns because now you can choose the lighter-weight feature patterns over the heavier group patterns.
With Pro/ENGINEER Wildfire 3.0 you can also embed datums within other datums, something that lets you streamline the presentation of complex geometries. For instance, rather than having to use the standard definition for a datum plane, you might want to modify it to support your design intent for a particular model. To do that, you can create a completely new coordinate system — an X-Y offset with an I-J-K rotation — and then insert the plane through the coordinate system’s X-axis. On the model tree you’ll see just the plane, but if you double click on the plane itself, you’ll see the dimensions of the underlying coordinate system.
The benefits of these changes are substantial, according to Gohil. Because the datums are embedded, they don’t clutter the model tree. Showing the dimensions on a drawing is faster than before, as is editing and modification. Most important, they help you establish and preserve your design intent in ways that weren’t possible before.
“Keystrokes, and the need to go back and forth between the model and the tree, can be a big deal, especially at the beginning of a model design,” says Gohil. “This is where the designer is thinking quickly, and he or she wants to get ideas down with as little interruption as possible.
“With embedded datums, we’ve now made the tool as powerful, and as unobtrusive, as possible, so designers can do what they do best — design — and feel confident that others will fully understand their creative intent.”
Smarter Models. At a higher level, the embedded datum capabilities in Pro/ENGINEER Wildfire 3.0 combine to produce what PTC calls smarter models.
“By embedding datums, users are really storing their design intent into the features themselves,” says Gohil. “When they share with other users, the design intent is documented and so can be easily understood — in the end, the result is a cleaner design, and a product that does what it is supposed to do.”
But that’s not all. In the case of embedded datums, ‘smart’ also means ‘reusable.’
“Reusability is a key design goal for all our software,” Gohil says. “So Pro/ENGINEER Wildfire 3.0 lets you drag the datum references outside of the feature node, to be used for other features, as well.
“That’s the best definition of smart I can think of,” he says, “to be both useful and reusable. That’s what we have with Pro/ENGINEER Wildfire 3.0.”
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