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Pretty much anything in a machine shop made in the last 80 years or so. So many people turn up their noses at anything that isn't computer controlled anymore. Yknow what a big old mill can do that a CNC can't? It can make every single part needed to make a new mill. It's a self replicating machine with the right know how. People don't respect that kind of quality anymore.
I don't think a mill can make the copper windings in the motor and isolate them. Same with the power cable.
You don't need an electric motor. You just need enough spin. I've seen old mills and lathes that run on steam. An electric motor just happens to be very convenient with our current technology.
Can a CNC not do that for just the mechanical parts?
(I know way too much about bootstrapping semiconductor production at small scale, which seems to be viable but highly impractical)
Sure, but it's not as impressive (imo) when you also need a computer control system, a bunch of circuitry and electronics, and a whole mess of software to make it work in the end. A mill just needs enough spin and it runs exactly as intended.
Oh yeah, I have a copy of the Gingery books and I love it.
I haven't seen Gingery into how much power you need exactly, or what blend of RPM vs. torque is ideal. What would be your guess, since it sounds like you might know?
Torque is the real limiting factor. You can always gear up or down for whatever you're working on, but at the end of the day you need enough torque to get the work done. And a proper milling machine needs A LOT of torque.
Can you give me some typical values, maybe? That would be a big help.
There are no "typical values" when you're running a mill or lathe. You could look up "speeds and feeds", but that's really just a table that you plug into an equation to figure out how to set the machine. It all depends on what you're doing and what you're doing it with. Drilling a hole with a high speed steel drill bit is going to be a bit different than drilling it with a carbide spade, and all that is going to depend heavily on whether you're trying to run through titanium or tin. You need to fine tune running "x" bit through "y" material for a "z" sized cut.
Essentially, this is the knowledge that separates skilled labor from manual labor, and machining is (was, RIP cnc button pushers) skilled labor.
At the end of the day for most metal machining you'll need between 50hp and 100hp to be up to modern standards. If you want to get that through steam or electric motors or whatever that's up to you
Thanks, that's really helpful. I suppose it makes sense that not just material but cut size and bit would matter. They usually focus just on the geometry on YouTube.
Out of curiosity, what's the lowest you've ever gone? It's hard to picture machining happening at something like 60RPM.
If you want to get that through steam or electric motors or whatever that’s up to you
Since I'm interested in technological bootstrapping more generally, I think most about water wheels, actually! Steam engines need to be machined, which is a chicken-and-egg problem (or I guess crafted freehand to a machining-like precision, like Vaucanson's lathe). Electric motors don't necessarily, but they need a source of electricity, and that's either a lot of batteries or another rotating power source, which again doesn't solve the problem.
Waterwheels can be made with hand tools - maybe even primitive tools - and can achieve surprisingly modern efficiency and power density. They do require the right topography, but then again they spin indefinitely without needing to be fueled. 50hp is still a sizable wheel, near the top of what existed in pre-modern times, but I'm guessing you can do basic things with an underpowered machine.
Yes, they make massive CNCs.