Surfacing in Alibre DesignOthers Saturday, December 26th, 2009
In a previous post titled “Alibre Design Vs SolidWorks” I wrote, “I don’t believe I could model the Christmas wreath or rose in Alibre Design without tearing my hair out“. Following which Alibre’s CEO, Paul Grayson, had someone from Alibre model a wreath in Alibre Design and posted a picture of it on his blog. I found this very interesting and it aroused my curiosity.
Over the past few years I have used Alibre Design to create quite a few parts and assemblies. But all of them were prismatic or “boxy” in shape. After seeing the image of the wreath in Alibre Design I decided to challenge myself to model my SolidWorks rose in Alibre Design. This is what I came up with.
Before I go any further let me state that Alibre Design has absolutely no surfacing capabilities. In fact, the documentation encourages you to import surfaces created in an external surfacing product like Rhinoceros. But this is not what I wanted to do. I wanted to see whether I could create the rose from scratch in Alibre Design itself. As it turned out, I succedded. All the geometry above was created in Alibre Design only.
Which begs the question, if Alibre Design has no surfacing capabilities, how did I manage to model this rose? Here is the thing. Surfacing is a term associated with the act of creating smooth curves which are used as profiles, guides, boundaries, etc. to cough up a smooth surface, something which has zero volume. These surfaces are then knitted together, thickenned, etc. to eventually create a closed solid which has a volume. In the case of the SolidWorks rose, I created four boundary curves (see here) and used the SolidWorks Filled Surface feature to create a surface which I later thickenned to get a solid petal.
Alibre Design does not have the abilty to create zero volume surfaces like SolidWorks does. But that does not mean that you cannot use it to create organic shapes like a rose petal. Since I could not use the surfacing route, I was forced to take the solid modeling route. Which meant that at every stage of the modeling process, I needed to have a closed solid. Here is a single petal modeled completely in Alibre Design.
And this is how I did it. I created a series of five closed contours of a petal on five different planes and used a Loft feature (Feature > Boss > Loft) to arrive at a solid petal. Here are the five contours.
Note that the bottom contour sits on the top face of the petal base. So after lofting, the petal and its base stay connected as a single solid. Here is the top view.
Its quite simple actually. My point here is not to show that Alibre Design can do surfacing like SolidWorks. It cannot. This is more like a hack, a work around to a better solution. I say this for a number of reasons. To name a few, modifying this design is going to far more difficult. In SolidWorks I simply need to change the four boundary curves. Here I need to mess with each contour and its plane. Adjusting curvature is not going to be easy.
But to me, the most important reason why I probably would not use Alibre Design again to model something like this is the fact that I could not make the petal as intelligent as I did in SolidWorks. If you remember I created three configurations (see here), one each for the inner, middle and outer ring of petals and used the base radius of the petal to intelligently deform each petal so that I could get petals of different shapes and sizes using the same SolidWorks part. I could not do this in Alibre Design, or at least I could not find a way of doing it. The reason is that in Alibre Design a spline is not that flexible as it should be. You cannot dimension the control points of a spline so that their positions can be driven by equations. At the most you can dimension the end points of a spline. This meant that I could parametrically move each contour around, but not parametrically deform it, which is what I was looking to do. If someone from Alibre or an Alibre Design expert user can find a way to parametrically change the control point positions of a spline, I would love to be enlightened. Please do leave a comment.
Of course, modeling the rose in Alibre Design using the solid modeling approach was a bit difficult, especially considering the fact that I had never done something like this before. But contrary to what I wrote earlier, I didn’t tear my hear out. It did get a bit frustrating whenever I wanted to do something and found that Alibre Design wouldn’t let me. But that’s probably because I was trying to do something that Alibre Design was not designed to do.
So if my job required me to do this kind of work frequently, would I use Alibre Design? I don’t think so. And that is precisely the point that I was trying to make in my earlier post. Alibre Design may not be the best tool for the job when it comes to complex modeling. But for simple and relatively complex tasks it works just fine.
In his post Paul Grayson wrote:
They want to turn the discussion into a feature war as a tactic to avoid the truth, which is that SolidWorks is overpriced and bloated with unnecessary features that most people don’t need, can’t master, and won’t use.
I am not sure I completely agree with that. For what it can do, I believe SolidWorks is priced just right. And for what it can do I believe Alibre Design is priced right as well. And here I am referring to the price of $999 for Alibre Design Standard, and not $99, or $197 as it is priced now.
If you are interested, the Alibre Design V12 part and assembly files of the rose can be downloaded from here. I have thrown in a STEP file as well in case you do not have Alibre Design V12.