Sometime recently I read about someone who acquired an older milling machine that had hydraulic feed on the table. I wondered about howthese tables might be controlled and if any lathes have been designed using hydraulics to move the carriage or crossfeed instead of lead or feedscrews. (After all, there are mechanical, hydraulic and pneumatic linear actuators.) I don't know if you could control hydraulics as precisely as feedscrews (with respect to headstock spindle rotation) for cutting threads, but you'd never have to worry about worn screws and metric/ inch conversions. I imagine that the big problem is in designing the feedback system and getting it to respond well. I've seen descriptions of hydraulic systems made by companies like Enerpac that control the balancing of bridge sections to keep them level while being positioned with cranes. I know that hydraulics can be controlled with electronics and proportional or servo valves. Probably it's difficult to beat mechanical feed and leadscrews because it's a simple and accurate system, but I was just curious.