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Sewing method
Introduction:
The sewing regroups boundary edges of the surfaces by pairs: most of the problems you will encounter will appear because TopSolid can find a pair for an edge.
Two cases have to be distinguished :
When an edge is alone (no other edge that fits with it), it will not be merged, and so it will be part of the boundary edges of the initial shape. It will result a hole...
When more than two edges meets together with the given tolerance, merging them would give an invalid topology (non Eulerian topology) that cannot define a solid shape: so the sewing will fail.
The sewing operation is only logic and does not modify the geometry, so if your trimmed surfaces are not well connected, and even if you manage to sew them, the chinks which separate them still exist. You can see it if you unsew the shape.
Method:
Associative mode:
The more usual method consists in sewing the surfaces with the function " Sew " by rising progressively the tolerance.
Generally, we start from 0.01mm and double this value at each iteration, and select the result of the precedent operation.
For each iteration, the number of solid created are displayed in the alpha bar. If not any solid have been created, the number of surfaces and the number of holes are displayed.
Trap to avoid: when you want to get a solid shape and you have got "1" surface with "n" holes, that means that you must fill up "n+1" holes, because one of the holes is considered as the natural limit of the surface !
Non associative mode:
In the NON ASSOCIATIVE mode of the function "sew", this iteration can be made on an automatic way: TopSolid make a first sewing with the tolerance value of the surface that fits this tolerance. Then, it doubles this value and make a second sewing with this new tolerance. This operation is repeated as many times as the number of iterations value you set.
Edges with problems:
When TopSolid meets coincident edges (with the given tolerance) it cannot merge (because the resulting topology would be invalid), it does not do it and let them free. In this case, the message "problems have been encountered at some edges" is displayed in the alpha bar and these edges are put in a conspicuous position by creating red curves on them.
There is many causes for the problems. The only way to correct this is to make a manual cleaning:
Elimination of the doubled surfaces.
Elimination of useless surface.
Limitation of a bad trimmed surface.
Plugging:
Generally, some holes subsist which cannot be automatically filled by simply rising the sewing tolerance. So you will have to create surfaces in order to sew them the shape to repair.
You can identify the holes in the surface by using the function " Curve | Other curves | Copy edge ", and selecting on the button BOUNDARY EDGES . In order to visualize better the very small holes, it is best to use the option Create mid points= YES and use a well visible marker type.
This possibility is also available when sewing by using the buttons: COPY BOUNDARY EDGES or COPY BOUNDARY EDGES WITH MIDPOINTS .
Once the hole has been identified, you can use the boundary edges to create a valid surface. The more useful functions to do that are: Flat, Ruled, 3-4 curves, Fill hole or Constraint.
