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Observations on Curvature and Surfacing
I'm pretty deep into a designing a new electric scooter for my company. There's a lot of surfacing work to achieve the industrial design. I've been taking a lot of advantage of Bézier curves in sketches, Bridging curve, Boundary surface and Face Blend. For the most part these newer tools are game changers for surfacing in Onshape.
- The curvature constraint in sketcher for Béziers is very "brittle". So many times a small change to the external references will cause a curve to go red. I can often fix it by deleting the curvature constraint and immediately reapplying it. Any time this happens, it means that the D-Cubed solver is not doing its job very well, or perhaps the way that Onshape is interfacing with it is not effective. We also really need a G3 sketch constraint.
- Bridging curve is very useful, especially now that it can take edges and surfaces as inputs. However, it also still really needs a G3 option. I wouldn't be fighting with #1 half as much if Bridging curve could do G3.
- Bridging curve is pretty slow to react to manipulator/value tweaks or rebuilding. It's not as fluid or interactive as other CAD tools, or even the sketcher. I realize it's often solving things in 3D, but it feels slow.
- With seemingly minor or unrelated tweaks to features upstream, Bridging curve often flips direction on inputs or edge direction changes and an edge position needs to be changed from 0.25 to 0.75. I realize that a lot of work goes into making these things robust, but even more robustness and intelligence would help. It seems especially frustrating when the curve you want is close to a straight line, and one or both ends flip and make something that pretty much no one ever wants.
- Boundary surface badly needs more upgrades (curvature constraints, internal guides, control over degree). In many cases it's better than Loft or Fill about making cleaner surfaces, but not always. It still sometimes increases the degree of the input curves without any obviously good reason, or it twists up the internal CVs in a way that the other tools don't. I'm also finding weird cases where Loft will take the same inputs and create a surface, but Boundary will just refuse to create anything. The error messages are not always clear.
- Face blend is very powerful, but takes a lot to really use its potential. @GregBrown did a good demo video, but as he alluded, there's so many combinations of options, it's hard to fully grasp all the power here.