By Scott Henderson
The Split command is an essential tool when working with surface-based models in the Generative Shape Design and Wireframe and Surface Design workbenches. It’ll let you take an existing surface that is a bit too long, then cut it down to the correct size and shape.
Doing a basic surface split is relatively straightforward. However, there are a few not-so-obvious choices and options in the Split dialog box.
Split versus Trim
Before we start, there’s another tool that looks very similar to Split – both in appearance and functionality – and that is Trim. The main difference between these two commands is that Split is only cutting specific surfaces while Trim will cut all surfaces involved in the operation.
The Basic Split
A standard, two-surface split is relatively straightforward to build. Fire up the command, pick the surface that is to be cut down, then click the items that will be used to cut it.
In the image below, I want to cut the blue surface and use the yellow one to chop it down.
After clicking Split ( ), the dialog box opens and I’ve selected the Blue extrude as the element to cut and the Yellow Extrude as the cutting element.
Based on how we’ve selected items, we could see either of the results below. To swap back and forth between them, click the “Other side” button. The side that has the pale yellow, default surface color is the one that will be kept.
After that, a quick click of OK gives us the final result. Not too bad.
Multiple Cutting Surfaces
Next, let’s take a look at the same example, but now we want to make multiple cuts to the blue surface simultaneously.
The initial plan is the same: Fire up Split, select the item to be cut, then pick the cutting elements.
This time, it looks like only the area to the right of the purple surface will be kept.
One of the slightly confusing things about the “Other side” button is that it refers to the other side of the surface that is currently selected in the Split dialog box. So, in the above image, Purple Extrude.4 is selected, meaning we are picking the area to the right or left of that surface. We’ll potentially have to do the same thing for the other cutting elements, choosing to keep what’s in front or behind the Pink Extrude and what’s right or left of the Yellow Extrude.
An easier way?
Since that can be a bit of work, especially with a large number of cutting surfaces, here’s the easy approach: While selecting the surface to cut, choose the portion of it that you’d like to keep. A lot of times this will happen somewhat “automatically,” as we naturally choose the larger portion of the surface or instinctively pick what we want. Be deliberate about it, though, and you can guarantee you’ll get the correct portion of the surface.
In the image below, I clicked the surfaces, but didn’t really pay attention to where I was clicking. That led to getting the surface on the left as a result. To get the center of the blue surface, I’ll need to play around with the “Other side” options.
On the other hand, If I specifically choose the center of the blue surface first, then that’s what I’ll get, making the Split command much easier to use and saving a little time, too.
Multiple Cut Surfaces
In addition to using several surfaces to cut a part, it may be that several surfaces need to be cut. In this case, be sure to use the 'Selection Bag' icon to side of the list to select multiple items. The same selection rules apply here, too, so be sure to choose the exact portion of the surface you’d like to keep.
In the case below, I’ve built a new surface offset above the original surface. I’d like to split it, too.
After clicking the Selection Bag ( ), we can choose the choose the large middle area on the Blue Extrude and Blue Offset.
And, as a result, both surfaces are cut down to the correct size:
A word of warning with this one: The splits may be grouped together in the tree, which could have some organization and/or feature hierarchy implications later down the line.
To the Point
Here’s the quick version: Want to cut a single surface? Use Split. Don’t like playing around with the options in the Split menu? Choose the area of the surface you’d like to keep, then the Split command will do just that.
More Flexibility?
Of course, this is just a look at the basic options in the Split command. There are more options and settings buried below and we’ll take a look at those in future posts. Also, by using more complex base surfaces, the complexities of the split will be increased as well, leading to more challenging scenarios. Not to mention, we haven’t even touched curves yet.
In both the Introduction to Surface Design and Advanced Surface Design courses from Rand 3D, we go through an in-depth examination of the Split tools and practice using them in real-world scenarios.
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