If you have a 16,000# machine on 6" of concreteit is moving more than you think.
Not too many gunsmiths are running 16,000lb lathes.
I agree, but most smiths don't have over a couple thousand pound rigs.
I was going to say the same thing... of all the gunsmiths I know I think the heaviest lathe any of them run is a South Bend Heavy 10 or similar and those aren't even close to 16K- more like 10% of that.... in any case, regardless of what your substrate is below your shop it will be helpful to lay down an extra bed of concrete where the heavy machinery is going to be placed. 6"-12" should be fine to help dampen vibrations in your machines IMO as long as it has sufficient reinforcement in the slab like heavy mesh or rebar...
Never underestimate your ability to overestimate your ability.
