The SolidWorks Boundary Surface

Recently I was asked by a reader to write about the boundary surface. This along with a lot of other stuff is covered in the surfacing book, but it’s not a bad thing to cover it again. The boundary surface has become my first choice for shape creation.

The Boundary Surface was added to SolidWorks a few releases ago, and then expanded in functionality. A Boundary Solid was also added to the software recently. The “Boss/Base” terminology is obsolete, and SolidWorks has removed it from most areas of the software, but the toobar feature names are one are where its use remains. The “base” part of it is obsolete ever since SolidWorks added multi-body capabilities, because it no longer matters which feature comes first. You can reorder the first feature. Further, since SolidWorks added the ability to turn a boss into a cut by dragging with Instant3D, they eliminated “boss” or “base” or even “cut” from the name of the features in the FeatureManager. Anyway, that doesn’t matter much, its just interesting background.

I have only used the Boundary Solid in one real part, so most of my comments here will apply to the Boundary Surface. Some, not all, comments can be applied to both features.

Mark Biasotti was a big advocate for the Boundary Surface when it came out. It was introduced in SolidWorks 2008, just as the surfacing book was being written. So I had to write the book with very little personal experience and absolutely no collective wisdom yet available. I made a lot of models and compared it against Loft, Sweep and Fill. Mark was a little incredulous that I compared it to Fill, but there were reasons.

Here are the main attributes of the Boundary Surface:

1. defined by curves in two directions – not called “profiles” and “guide curves”,  just Direction 1 and Direction 2
2. can use curvature continuity condition for edges in either direction – loft only can apply c2 to profiles
3. accuracy of actual surface to sketched curves is better for boundary than other features except Fill
4. can use sketches, curves or edges, just like loft
5. can use different arrangements of curves – loft with g.c. looks like “H”, and a sweep like a “T”, but boundary can use X, L, E, A, just about any combination where Dir1 and Dir2 curves intersect
6. you can use boundary like a sweep, but it works as if you used the “Keep Normal Constant” setting
7. you can use a point as a curve in one direction, lust like lofting to a point
8. the only loft(s) that you cannot replicate with boundary is are the Centerline Loft, which is like a sweep with multiple profiles where the profiles do not touch the centerline and the closed loop loft. (oops – edited because I left out one)

This is going to have to be a multi-post topic. There is too much to write on a Sunday afternoon when the SolidWorks Customer Portal is down for maintenance. Here will be some of the other post topics:

• boundary examples
• comparisons to Loft, Sweep and Fill
• accuracy/tolerance
• boundary limitations
• curve selection techniques
• evaluation techniques