I'm trying to build a CNC machine that can mill steel. After a bunch of reading, I've come up with some design ideas based on a steel-reinforced cement frame. Here's an unfinished prototype I made to test vibrations: By the way, I don't plan to use a corexy setup. Anyway I think the cement frame will work, but after watching a bunch of YouTube videos of homebuilt CNC routers I think I've spotted another problem: the spindle drive. Most people seem to be using spindle motors that spin really fast and are directly attached to the collet (either a dremel tool or a special-purpose spindle motor). I can see two problems with this approach: first is the side load put on the motor bearings, and the other is just the problems you get with high-speed brushed motors. Industrial milling machines are belt-driven, as are prosumer "Mini Mills". What I'm thinking of doing is something similar to the Mini Mill: have the motor on the spindle head, but connected to the spindle via a belt and a stepped pulley (to get different speeds). The motor itself would be a three-phase induction motor driven by a variable frequency drive. Anyway, let me know what you think. One decision I've not made yet is how big this machine is going to be. Obviously it won't be as small as the test prototype, but I would like a reasonably small machine.