Kous

Make sure that the model is a subgroup of Part Tools in the hierarchy panel. I was having the same problem and dragging the model directly on top of part tools fixed it.

Nice looking models. You could have the fusion reactor produce Neon or Argon which have reasonably lower ionisation energies.

I figured I would share some models I've been working on. The first is a 3.75 metre crewed can basically so you can make a Kerbal Skylab. The second is a 3.75 metre dome. I also uploaded a bunch of junctions to supplement the hubmax part. Although I'd like to redesign some of the windows. Now I just need to learn to make textures. P.S. Shoutouts to ClairaLyrae and bac9 for making stock like parts and mentioning that sketchup can be used for mesh modelling respectively (Blender is infuriating).