Here is the error with a tube and fem on the ends that are octagons.
I will include the file the error and the pic
windows 10 freecad .17

- circleerrorgmesh.png (155.57 KiB) Viewed 476 times
0.0: We are going to start ...
0.0: Start Gmsh ...
1.5: Gmsh had warnings ...
1.5: Warning :

There are 3 intersections in the 1D mesh (curves 24 20 25) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 10 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 27 28 30) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 12 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 16 20 25) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 10 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 27 29 28) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 12 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 18 20 25) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 10 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 30 29 27) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 12 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 12 16 25) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 10 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 30 32 27) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 12 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 14 16 25) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 10 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 31 30 27) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 12 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 12 14 25) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 10 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 32 31 27) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 12 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 24 12 25) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 10 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 32 34 27) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 12 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 33 32 27) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 12 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 34 33 27) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 12 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 27 28 34) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 12 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 35 34 27) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 12 consists of no elements Warning :

There are 3 intersections in the 1D mesh (curves 27 28 35) Warning : 8-| Gmsh splits those edges and tries again Warning : Surface 12 consists of no elements Error : Self intersecting surface mesh, computing intersections (this could take a while) Error : Could not open file 'intersect.pos' Warning : Volume 1 consists of no elements Warning : Surface mesh: worst distortion = -1.53331e+14 (avg = -9.70701e+11, 5 elements with jac.
1.5: Gmsh done!

- circleerrorgmesh.png (155.57 KiB) Viewed 476 times