Any Freecad experts?

[Mjolinor]

I am trying to draw a lens holder / air assist nozzle thing for my laser cutter.

All the parts are there and correct. I have made a fusion of the outside and now need to make a fusion of the inside then cut that away from the outside. The fusion of the inside bits will not work. I can bluff my way round it by making the fusion in pairs but then when I cut it away from the main outside I get a pile of crap.