If you ever want to involve your teenaged son in this hobby, just tell him he gets to use the blow torch! In fact, I think you could convince a teenaged boy to do just about anything if it involved a blow torch. It’s unfortunate that they can’t use one to clean their room without also cleaning the rest of the house into oblivion.
The Boy and I spent half an hour or so today verifying that yes, we can easily fill a cavity with molten lead. No the blow torch will not accidentally turn 3D-printed steel parts into slag. And yes, you can drop molten lead onto Kapton tape without losing the insulating property.
It was cold and rainy so we then retreated indoors to hot cross buns, tea and a game of chess.