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.
a - build a big machine, you need space for the tool and the clamps/vice. b - research 'SFM' and 'feeds and speeds for steel' so that you know the range of spindle speeds you will need. Also research how much horsepower you need for cutting steel.
That's a good point about the tools and the vice. For the motor I was thinking I'd start at 3/4 hp and go up from there. I'd like to be able to run this on less than 1500 watts if at all possible.
Steel reinforcing doesn't do anything for concrete until it cracks. But once it cracks the system won't be of much value anymore as now you'll have vibration in the system. If you're only looking to do small pieces, I suggest converting a Harbor Freight Mini Mill to CNC.
I admit I have trouble believing that too, which is why I built the prototype to test. I've not done so yet, but I can already tell that just the mass and stiffness of a concrete frame is going to help, even if it turns out not to dampen vibrations like people said it would. On the mini mill, I may end up doing that, but what fun is that
