I'm not sure what is harder to mill than steel... I'm sure there's heaps of stuff out there but assume I want to get a spindle that is able to mill some really hard stuff... what spindle wattage would I be looking at? I don't have any materials in mind at the moment, however I'm thinking more for the future... maybe I'll bump into something that is harder than steel and it would be nice to buy a spindle that will be able to handle those kinds of materials.