VSS - justification

I'm starting to get my course notes updated for next semester and am again
at the Variable Section Sweep.
Every year I get to this section and come upstuck in finding good real life
example of its application - those endless bottles and abstract edge ribs
really aren't very convincing for why my students should learn this
function.
If anyone has a some good real life application which really show the power
of this feature they would be gratefully recieved.
As soon as I show any examples* the question is why don't you use a boundary
blend? - you have control over both end sections and you can 'fill' between
existing sections. As I understand it you will generally get a smoother
surface with a VSS - is the reason for this easy to explain to undergrads?
I tend to sell it very much as a base feature or [as alot of the tutorial
examples] a sweep along existing edges.
Thoughts on this in terms of convincing students its worth understanding
what is one of the more complex functionalities in the toolbox would be
gratefully recieved.
BTW - remember how rudimentary their knowledge is - I sometimes struggle
getting them to grasp tangency and normalcy!
Cheers, sean
Reply to
Sean Kerslake
Loading thread data ...
: I'm starting to get my course notes updated for next semester and am again : at the Variable Section Sweep. : : Every year I get to this section and come upstuck in finding good real life : example of its application - those endless bottles and abstract edge ribs : really aren't very convincing for why my students should learn this : function.
One of the most exciting things about learning Pro/e was the discovery that there were always manu different ways to model the same part. Even the starting points could be quite different: start with a little piece of the part (one feature) and add features? or start with a big block and starting cutting the features out of it. Part discovering the rich variety of feature creation methods and styles was realizing that even a simple 30mm x 50mm x 10mm block (sketch and extrude a rectangle) can be made three different ways: sketch a 30x50 rectangle on the Top plane and extrude 10mm; sketch a 10x50 rectangle on the Right plane and extrude 30mm, etc. : : If anyone has a some good real life application which really show the power : of this feature they would be gratefully recieved. : : As soon as I show any examples* the question is why don't you use a boundary : blend? - you have control over both end sections and you can 'fill' between : existing sections. As I understand it you will generally get a smoother : surface with a VSS - is the reason for this easy to explain to undergrads? : In addition, as I gained some sophistication in using the software and realized that there were usually several ways to create a feature, I started experimenting. If a feature could be made as a blend or a swept blend or an extrusion with a bunch of cuts, I tried them all. I evaluated them by the results achieved, by how easy they were to modify, by limitations in control of shape or attachment or surface continuity, and by their complexity and the time it took to create the feature. Along the way, I gained mastery of Pro/e's surface and curve analysis tools. When you're trying to evaluate the results of different methods, you can't rely on the unaided eye; you need 'porcupine' or 'highlight' analysis to see discontinuity. And, by these means, you'll also see the influence of the curve foundation on surface quality.
Because of the curves that boundary blend surfaces are built on, they are usually the most troublesome. Part of it is the fact that boundary conditions and how high a degree of continuity you can impose depends on the curves and their end point tangency. So, building the curve framework that can support the highest degree of surface continuity is an art in itself. It is compounded by two things: by the number and size of the patches and by whether you *begin* with boundary curves. You have probably noticed that when you have a series of patches to construct, the first patch has no other surface to which to set 'surface curvature' boundary condition. That was the reason for introducing, in the last few revs, the Datum Ribbon. Before that, the best you could do was to set the surface at a boundary normal to a plane. One or two could be helped this way, the rest were left free to go where and how they would. Sometimes the problems didn't show up until the adjacent surfaces were set 'surface curvature' to this first patch. Then you'd get wrinkling or twisting. This type of problem was the basis for introducing another aid to good, curvature continuous surfaces, namely ISDX, which carries boundary blend surfaces to the next level. In any case, there are enough problems using boundary blend surfaces that I pretty consistently use them only for patching or blending between features.
The VSS has none of these difficulties or defects. With smoothly curving trajectories and cross section curves, you produce the smoothest surface possible. And with less underlying curve geometry and with just as much control of tangency at the start and end of the swept geometry as with boundary blends and swept blends.
: I tend to sell it very much as a base feature or [as alot of the tutorial : examples] a sweep along existing edges. : : Thoughts on this in terms of convincing students its worth understanding : what is one of the more complex functionalities in the toolbox would be : gratefully recieved.
Again, the use of a variety of techniques, experimenting with different feature creation methods will do it's own proving, its own arguing. The only general argument that can be made for learning more technique(s) is that it makes choice possible. Ignorance will make the choice for them and their "reasons" for not using VSS or any advanced techniques, including boundary blends, will sound like sour grapes. Choice means being able to weigh and compare based on experience and they won't have any experience by avoiding learning VSSes. And the best you can do is practice and teach the first rule in life and learning ~ don't panic, it's probably not as bad or as hard as you think.
David Janes
Reply to
David Janes

Site Timeline

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.