I have never cut slate, but from what Ian says, your best bet will be the typical machine build from forum members, recessed bed, strong gantry on none or low gantry legs. Square supported linear bearings size 20 at least and ball screws. Even better would fixed gantry machine, something like that, you missed it by a week http://www.mycncuk.com/threads/8510-...l-up-for-grabs

The table bed working area in both cases being low means the visible ball screws and bearings will remain more or less clean. In fact you dont need water bed, something like fogless mister should work ok without making a big mess.

Now the difficulty comes that i don't know for a commercial machine that has the qualities of a diy build at acceptable price. So your best bet will be sb to build it for you, yoiu to build it your self , plenty of info here or wait something to turn on the market, but its very rare sb to sell such good machine.

Take a look at my first build for a friend bellow, the link in the signature. The machine is 1000x400x180 working area and will do what you aim, even much more, is simple enough to build, there are free plans in sketchup somewhere inside, it could be a good starting point

The other type of machine that guys here usually make is a bit different from mine. Gantry is aluminum plates forming a beam, bed could be moved up and down for special job. At the end depends on your priorities and ability to machine aluminum.

Hope that gives you a good idea what you need.