NX7.5: My First Class-A Surface p.2

As a follow-up to the NX post from yesterday, here we’ll take a deeper look at the NX interface, the power of associative parametric modeling, and some tips and tricks for clean surface modeling. Check out the full article for transcription.

Transcription:

If you watched yesterday’s introduction to NX 7.5, you’re probably thinking ?Big deal. So you made a surface. Who cares?? Let?s dig a little deeper into what we?ve accomplished so far, introduce a few more interface tips and tricks, and focus on the power and flexibility of building surfaces this way.

1) Let?s take a look at a few more interface tricks.

First, click the little ?gear? widget underneath the NX icon in the toolbar manager, and select ?Collapse.? This lets us get away with only the bare essentials on our screen: we have access to every tool in NX via the menubar dropdown, and dropdown access to all of the toolbar manager tabs from the ?All Toolbars? dropdown. This is my favorite way to work. If you prefer the full toolbar, feel free to click the ?gear? widget and select ?expand? to bring it back.

Finally, you may find that sometimes you want tighter control over the middle-mouse viewport rotation. First, you may want to control the center of rotation. The quick way to temporarily change the rotation center is to simply hold the middle-mouse button on a piece of geometry until the blue crosshairs appear, indicating the newly defined center. To set a ?persistent? rotation point, right-click on the background of the viewport, and select ?set rotation point,? then click a piece of geometry to set the persistent rotation point. To go back to the default rotation, right-click and choose ?clear rotation point.?

Finally, there may be times when you want to rotate about an axis. By clicking any one of the axis in the viewport rotation indicator at the bottom-left, we can constrain rotation to the selected axis. To go back to full 3D rotation, click the sphere at the center of the indicator.

2) Everything we?ve built so far is ?associative.? Put succinctly this means that if we change any piece of geometry, all of its ?children? will update accordingly. For example: if we double-click on our associative Studio Spline, the dialog reappears, and we?re able to make changes to the curve.

For those of you who?re already accustomed to working with NURBS curves, you may be interested to note that in the ?Analyze Shape? tab on the toolbar manager we have access to a button called ?Curve Analysis ? Combs.? This will simply toggle a porcupine curvature graph on and off as you?re working, allowing you to see the curvature you?re creating in real-time. Click the button again to turn off the curvature graph when you?re done.

When we click ?OK,? the surface geometry is updated. Likewise if we were to double-click one of our support surfaces and add a draft angle to it, the draft would be reflected in our conic sweep. Thinking about modeling in terms of associative history will take some getting used to, but it?s well worth the effort in terms of downstream speed and flexibility.

Thus far we?ve been interactive with our geometry solely in the 3D viewport, but there?s another way: toolbar manager > Resource Bar > Part Navigator gives us a list of every associative element in our model, listed in the order in which it was created (the order is very important, as we?ll discover later). As you can see, selecting an item in the Part Navigator tree highlights its counterpart in the 3D viewport. Double-clicking an item in the tree allows you to edit its parameters, just like double-clicking in the viewport.

If you prefer to see your geometry update in real-time as you make adjustments to your curves, head to menubar > Preferences > Modeling > Update tab > Dynamic Update > Continuous, and set ?Dynamic Children? to ?All Level.? Instead of double-clicking a feature to make changes, right-click and choose ?Edit Parameters? (as opposed to ?Edit With Rollback?), and watch your surface update in real-time! With complex models this will become prohibitively slow, but in simple situations like this, it can be quite convenient.

3) I told you before that this isn?t just any swept surface: this is a clean, perfect, Class-A quality surface. Le? me ?splain:

First of all, lets take a look at the topology of this surface by selecting it, then clicking Analyze Shape > Show Poles and hitting ?esc? to drop the selelction. The first thing you should notice is that each ?rib? along our sweep contains exactly four control points: the bare minimum required for this shape. If we head to the top view, notice that the points on each rib are perfectly aligned to one another, perpendicular to the curvature of the ?Spine? curve.

I promised in the last video that we?d talk about ?spine? curves at length, and we might as well start that discussion now. If you?ll recall, when we defined this surface, we chose the StudioSpline as our ?Spine? curve. We can now see the result of that decision: the ?ribs? of the surface are always ?normal? (or ?perpendicular?) to the spine. This gives us incredible control of our surface.

For example, let?s use toolbar manager > Lines and Arcs > Line Point-XYZ to create a perfectly straight line down the center of our model, and hit ?esc? to drop the tool when we?re done. Notice that the line is represented in the Part Navigator tree, AFTER all of our other features. I?d like to use this new curve as the spine for our Section Surface, but when I double-click the Section Surface, notice that the line is no longer available to me to click: it?s disappeared. This is because the line was created AFTER the sweep, and as such is not available at that point in the part history.

To make it available, we?ll need to drag the line in the Part Navigator so that it?s anywhere ABOVE (or BEFORE) the Section Surface in the list. Now when we double-click the Section Surface we can select the line as the spine curve for our surface. Notice that the ?ribs? of the surface are now in a perfectly straight line.

Taking advantage of ?spine? curves gives us incredible control over the quality of the end surface, to to mention its shape. When we select the surface and use toolbar manager > Analyze Shape > Face Analysis ? Radius, we can see that the curvature across the surface is perfectly smooth, with no ripples, curvature inversions, or bunched up areas at the ends.

If we use Curve > Intersection Curve, select the Section Surface as the first parameter, middle-click, and select the ZX plane as the second parameter, we can then select the curve and use Analyze Shape > Curve Analysis ? Combs to see that the curvature is perfectly smooth, and perfectly convex with no wobbles or inflections. This is the beauty of conics: by definition, a conic can mathematically NEVER have wobbles or inflections.

We can adjust the ?sharpness? of the surface by adjusting the Rho value between .01 (extremely flat) to .99 (extremely sharp). But even with extreme settings like these, tangency is maintained, and the quality of surface remains perfect.

If we really want to be fancy, we can even vary the Rho value across the length of the sweep using a Law function. Simply double-click the feature, set the Rho Law Type to ?Linear?, and select a start and end value. We don?t need to eyeball anything: we know that the surface is perfect.