Friend with wood floor shop had same problem, he solved it by cutting hole in floor, framing it in, then pouring full of concrete. Might not be an option for you
Last time I saw his shop we had just moved in a 4000lb lathe, it was sketchy, getting close to lathe you could feel floor sag. My suggestion at that time was frame around exterior of building, cut 4" holes throughout floor, and start pumping concrete.
It need not be all that hard. Now - if in RENTED space, not owned, yah...
Example IF there is a full basement under, 8-foot+ slab to overhead, and clear space not already allocated.
4" x 8" nominal, beam each side of a 6' x 6' rectangle, on columns. Cross joists at right angle to the originals, fit to load taken up / leveled with wedge-shims. Spaced according to load, the 6' span joists need not be all that deep. Now you have an area with only 7-foot or so overhead.
BFD.
Typical 5/8" plywood flooring simply DOUBLED can support average passenger cars for an automobile showroom floor.
CAVEAT: Yes, done this. No, am not an RPE.
Get proper advice and follow that advice for your actual, not "hint at" situation.
It is cheaper and easier than building a "panic room", for example.
Which it could become.
Or a preserves and food closet, (as one of our ones became), or.... lot's of things more useful than a solid mass of ignorant 'crete.
It can even be removable and portable to the next challenge, just as has to be done all the time for lots of construction or rigging projects.
And "Oh BTW?"
WTF WAS going through a tiny little MIND
NOT ....to put that lathe there to begin with without doing some basic structural checking and getting advice FIRST?
Had an Uncle by marriage that klever-klewless onct. Went-over from dairying to raising chick'ns commercially.
Got rolling good, built him a second-story onto a chickn' house to double his capacity.
Used him 2 x 4 joists where 2 X 12 shudda been to keep the cost down. Figured chickn's weren't very heavy, after all.
3/8" plywood floor over them 2 X 4's sagged when he walked through to distribute feed, but no big deal, old cow-patty-hopper was sure-footed enough to not lose his balance.
Got him a surprise one day when my Aunt came in to feed from one end, he came in from the other end, and three THOUSAND chikn's took flight to go for the feed.
And then all three thousand of those "not very heavy" cluckers LANDED at near-as dammit the same time!
Well.. nobody died as didn't have feathered wings already.
And there was chick'n shit and nitrates enough on and in the plywood the wreckage burnt up right nicely as well.
You'd have to know French Creek, West Virginia..."back in the day".