Is it possible to build a 6-in-1 mill/lathe machine like the one shown at Amazon.com: KKmoon Mini Metal Lathe DIY 6 in 1 Multi-functional Motorized Transformer Multipurpose Machine Jigsaw Grinder Driller Plastic Wood Lathe Drilling Sanding Turning Milling Sawing Machine Tool Kit: Home Improvement ? Most of these machines are junk and I still have V-Slot and C-Beam left over after rebuilding my CNC router.
Most of the features it offers are a joke. I would probably focus more on building one piece of equipment that does one thing very well like a mini lathe. (and if you're going that route, consider creating a fourth axis for your router instead.)
I don't need the CNC features. I want an all-in-one machine with X-Y table. I know that if I put CNC motors on it and I spin the lead screws moving the X-Y table, the motors become generators that may damage the drivers.
If you’re just looking for a hand cranked xyz apparatus you can hook attachments to the minimill is probably the best source of inspiration. You’ll just want to go with a low pitch lead screw or it’ll be moving on it’s own.
Single start acme/trapezoidal screws, bronze nuts and a good helping of grease. Considering how different all those machines are, I doubt I'd consider building anything beyond a 2-in-1 of something that happens to line up well (a tool grinder isn't too dissimilar from a watchmaker's lathe, for instance). You can also just get an XY table, like this one: https://www.amazon.com/Lukcase-Multifunction-Worktable-Compound-Heavy-Sized/dp/B071V8PJ1S
When you spin a stepper motor by hand, it generates a current that can damage a driver chip it one is not careful.
I'm not saying that it can't happen but I've seen so many YouTube videos where people move the gantries by hand, on their 3d printer, and never heard of someone burning their driver. I did it many times on both my 3d printer and my CNC router. That doesn't mean it never happened, though. Peter said if we'll remind him, not on a weekend, to do a scope check he may do it! It's not a weekend!
My first thought on 3d printers is maybe there are some form of diodes on the motor leads to protect the driver. I did a search and ran across EMF Calculator RepRapFirmware.org It has a back EMF rating not sure I understand it. Just thought it was pertinent info. Some post out there state there are some form of diode built in on drivers, most likely commercial/professional boards are built with them. There is a possibility that the home built CNC cheap stepper drivers you can get might not be protected.
Back-EMF is something totally different - its the self-braking effect of a stepper motor. Our motors are low-inductance, some 3rd party motors are not, and thus suffer self braking at much lower RPMs (stalling) than our motors.
