3 ms·

Just to add to this, fillets may seem trivial but they are a good example of the difficulties in parametric cad. Fillets are added to edges, edges can be forme

Just to add to this, fillets may seem trivial but they are a good example of the difficulties in parametric cad. Fillets are added to edges, edges can be formed both by a single feature (say an extruded 2d shape) or through the interaction of two or more other features (think of two extrusions 90deg to each other interacting and forming an edge). They can also link together or become unlinked via changes. Referencing these edges, and keeping track of that reference through changes to the parameters is fundamental to parametric cad. It's one of the areas that OpenCascade struggles with.

regularfry 4y ago
Judging by where it fails, the filleting itself in OpenCascade has no problems keeping track of edges, where it seems to have difficulty is 1) saddle points, and 2) where the fillet size makes it intersect with a feature it's not responsible for. A fillet breaking when a parameter update changes the topology is just a specific example of the topological naming problem. I don't think that's specific to OpenCascade. In fact, just thinking it through, I wouldn't be at all surprised if 2) above is the same thing: the fillet itself changes the object topology enough that the basis edges for the fillet get lost. If so that's a Freecad thing rather than an OpenCascade thing. Maybe someone who's worked in that area can comment, it might be one of those things that gets better in 0.21.
- catherd 4y ago
  FWIW, fillets give Solidworks trouble too. Never build child geometry on top of fillet parents if you can avoid it because it's likely to blow up on later rebuilds.
  - iancmceachern 4y ago
    True, but this isn't having so much to do with the fillet itself, but with the child geometry referencing outputs of the fillet command like edges and surfaces of the fillet. It you go back later and then change the fillet radius, delete it and add another in its place, etc. Those references get messed up.

regularfry 4y ago

Judging by where it fails, the filleting itself in OpenCascade has no problems keeping track of edges, where it seems to have difficulty is 1) saddle points, and 2) where the fillet size makes it intersect with a feature it's not responsible for. A fillet breaking when a parameter update changes the topology is just a specific example of the topological naming problem. I don't think that's specific to OpenCascade. In fact, just thinking it through, I wouldn't be at all surprised if 2) above is the same thing: the fillet itself changes the object topology enough that the basis edges for the fillet get lost. If so that's a Freecad thing rather than an OpenCascade thing. Maybe someone who's worked in that area can comment, it might be one of those things that gets better in 0.21.

catherd 4y ago
FWIW, fillets give Solidworks trouble too. Never build child geometry on top of fillet parents if you can avoid it because it's likely to blow up on later rebuilds.
- iancmceachern 4y ago
  True, but this isn't having so much to do with the fillet itself, but with the child geometry referencing outputs of the fillet command like edges and surfaces of the fillet. It you go back later and then change the fillet radius, delete it and add another in its place, etc. Those references get messed up.