How can I make the Bishop's hat in the chess piece? I have attached a blender file below along with some pictures. I tried to use the boolean modifier to do the same but came up with rather difficult to work with results. I want to have the curve and the shape of the hat to be nearly the same as the real Staunton Bishop.



gdrive link to blend file: https://drive.google.com/open?id=1x1poqr1abMpW_miAbRIkWpvRVR0twlMc
First close the top of the mesh, then put the Boolean modifier above the Subdivision Surface and use a shape like this one and it seems to work fine.  When you're glad apply the modifier and bring some corrections so that the mesh is clean: Quads instead of ngons, bevels to sharp the edges, etc...