I built a stand for my (new to me) drill press! Everything is nice and square, and I'm really proud of the result. And then I put it on my not so flat garage floor... And the locking casters aren't all that effective anymore. It's also pretty wobbly. Any tips for placing movable tool stations on wonky floors? Smoothing the floor sounds like too much work!
Yes, but you might have to build a new cart.
A three-wheeled cart will always be stable. Three points of contact will form a plane on any uneven surface. However, the three wheels need to be spread out more at the base, so that the weight on the cart can't be tilted past a line formed by any two wheels (if the weight goes past one edge of the triangle formed by the wheels the cart will tip over).
Another option is to mount two wheels on a tilting axis that allows one side of a four-wheeled cart to adjust to the uneven floor (a bit more complicated to build).