[techdog]

Would 2 nema23 run a gantry on a homebuilt cnc with a bed of 2feet by 4ft? chain driven or is that overkill?

[ger21]

It depends on how fast you want to move, how fast you want to accelerate, how much weight your moving, and whether you're direct driving the chain or using some type of gear reduction.
Also, Nema 23's come in hundreds of sizes, each with different properties. Add in the many different drives available, and you could have hundreds of combinations to go with the questions above.

But generally, I'd say yes and no, to answer your two questions.