[Aelinsaar]

I think by "Black hole generator" the other person meant a device which could create black holes remotely through some kind of process, not just a mass that collapses under its own gravity. In that sense, if you could find an old, spun-down neutron star (and man wouldn't that be a fun search! Massive, but tiny and dim...) then as you say, you could just keep adding mass until crush.

[fizx]

Any black hole generator that doesn't itself become a black hole is essentially throwing part of itself in the black hole (Yay conservation laws!). You can replace the catapults with lasers or plasma guns or whatever.

[Aelinsaar]

Sure, but I think the original commentator was imaging a massive sphere that could emit such powerful and precise gravitational waves, that you could create more black holes as a result. My point was just that any mass capable of achieving that, even hypothetically, would have long since collapses into a black hole.

I take your point however, that you could coordinate in some way separated masses, but at some point you'd probably run into issues with the aforementioned galactic-scale of engineering.