Betcha Didn’t Know This: Fill Surface

I have long called the Fill surface the “magic wand” in SolidWorks. It enables you to create a great range of stuff and does things it shouldn’t. This aircraft model, for example, has a lot of surfaces that come to a rounded point, or started flat and needed to be bulged somewhat. Fill is great at this.

Did you know:

• You can use a point as a constraint curve in the Fill feature to make a surface bulge?
• Fill also enables you to knit together all of the involved surface bodies?
• Fill will also create a solid if the knit results in a watertight volume?

This kind of shape used to be difficult to create. The Fill surface has been around for a long time, but I think there are still some people who don’t know some of this functionality. The image above is from the rear section of the engine cowling. I used a 3D sketch point as the constraint curve.

Of course this could also be done as a Boundary surface with a spline defining the back of the curve, but if you look closely, the Boundary surface creates a degeneracy on each side, while the Fill surface creates no degeneracy. Degeneracies sometimes cause problems with downstream features that have to interact with the edge where the degeneracy occurs, especially stuff like fillets, offsets, shells, and so on.

And while we’re here, we might as well point out that most of these surface features enable you to show the UV mesh to see things like degeneracies before you build a whole model dependent on that kind of (otherwise invisible) defect.