It's the way we connect

I don’t know what tops your list of favorite activities, but for me nothing beats  “Date Night”  with my hubby.  Whenever we have a chance, we leave the kids with a babysitter and head over to the most romantic place in town. Why, the bowling alley, of course! OK, so it’s not precisely what the dictionary describes as romantic, but we always have a great time there, and part of the fun comes from watching other people bowling.  Everyone has their own style. From the fragile-looking little girl, who barely holds the ball with her fingertips and gently places it on the lane, yet manages to knock down every single pin 90% of the time,  to the tough-looking, 6’4” and nearly 300 lbs guy, who seems to cradle the ball in his arm as he approaches the lane, then sends it flying  in the air, so it will land half-way down the lane, follow a curved path, and knock down all the pins, also at least 90% of the time. It’s a good approach! I tried it myself and made a strike. Unfortunately for me, I scored it in the neighbor’s lane. Anyway, at least in recreational bowling, the way you make it from A to B doesn’t seem to make much of a difference (although it is somehow important when buying yourself a bowling ball), but it does matter when in solid modeling, particularly, when you’re working with lofts.

One thing I’m learning is to be mindful not only of the way you pick your profiles for lofting, but also the way you prepare such profiles for the operation. Lofting allows the user to create a solid, surface or cut that is defined by several cross-sectional profiles, by interpolating  geometry  between  said profiles. This allows us to create smooth transitions between very different profiles.  However, the way you pick those profiles has a lot to do with how smooth that transition actually turns out to be, and, in fact, if you aren’t  careful, you can end up with unwanted twists, ripples, or even a loft that will fail altogether. If you ask for advice, people usually tell you that what you need to do is pick corresponding points on each profile. Hmmm, well, that would be easy if you were lofting a couple of squares, but what if one of your profiles is a closed semi-circle and the other one is a rectangle? Well, there’s also that other piece of advice that you don’t hear very often but that comes in handy for this kind of situation: each profile should have the same number of segments.

What does it mean for the profiles  to have the same number of segments? Well, if you look carefully you’ll notice that when you pick your sketches, edges or surfaces for lofting, SW generates  connectors that show you which vertices will be connected with each other during the loft.  If for example, one of your sketches is a square, it will have 4 vertices, that will have to connect in, at least  four different points with the other profiles in your loft. If your other profile is a circle, the system will divide it in four different segments, so it can create the connectors as needed. This may or may not give you the results you expect. You have better chances of succeeding if you divide your profile in segments yourself, so that the number of segments is not only the same in all profiles, but the location of the points where the profiles would connect with each other also corresponds to your expectations. In the following image, a closed semi-circle(2 segments) is lofted to a heptagon (seven segments), without any previous preparation.  SW has divided the semicircle in segments and created connectors between both profiles. Notice how the loft  is twisted, even though I tried to pick the profiles in points that seem to correspond to each other. By the way, if you can’t see all the connectors in the preview of your loft, simply right click on the graphics area and select Show All Connectors from the menu.

You can change the location of the connectors by picking and dragging them  (by the blue dots) in the graphics window. You can even add extra connectors as needed. The  number of connectors and their location is going to affect the transition between the profiles in the loft, as you can appreciate in the following image, where some connectors have been moved and others added, kind of willy-nilly,  merely to illustrate this fact.

As I said before, you can also prepare your profiles for lofting, by dividing them in equal segments yourself, according to your design intent. In order to do that you can use Split Entities, from the Sketch Tools. Simply select the entity you want to split or divide in segments. A split point will appear on the entity, near the location where you selected it. Use relations or dimensions to correctly position the split point where you want it to be.  Notice the difference between the following loft from a square (4 segments) to an octagon (8 segments). In this one, the system divides the profile in segments.

In this other one, I divided the square in segments myself, placing split points in the middle of each side. Looks better, doesn’t it?

There are other ways to affect the transition between the profiles in a loft, like the use of end constraints, centerlines, and guide lines, but I’ll have to tell you about those some other time, because I’m still working my way through them. Now it’s getting really interesting! I think I’ll never tire of exploring what else can be done in SolidWorks! Definitely nothing to do with what I used to draw in AutoCAD years ago!

Comments

[nkquz]

Good work...nice tutorial ^_^

[Gabi]

Thanks! You have some impressive work there on your site!