I can't transform an object from Mesh to Brep

[Anonymous]

Hello 

I have reduce the mesh but when I want to transform into BRep.

Here is the icon it puts me. (it's not the square, it's an open cylinder)

Suddenly I am blocked I would like to pass my piece to this state I think that is what blocks me to make a mold with  "combine" option I can not select my body

Thank for you're attention 

[TrippyLighting]

Converting a precision mechanical components such as a gear directly into a solid is a terrible idea IMHO. You;'ll loose that precision. That s particularly true when reducing the mesh!

The orange cylinder (not done reading through the documentation yet, I assume ?) indicates that the mesh was converted into a surface body. You'll have to find the hole, patch and stitch it to get a solid body.

For more organic models there are other workflows involving T-Splines, which are much more suitable for working in Fusion 360.