of your own, Crawler. Unfortunately, they aren't paticularly good ones...
First off, a Jacobs chuck isn't the right thing to hold endmills with. The reason people use collets on their CNC equipment is to cut down on run-out, the wobble that will break your tooling and ruin what cuts you manage to make before that happens. The smaller your tool, the more critical this "TIR" factor becomes. Also, you need considerable rotary speed to cut aluminum, especially with small-diameter bits; the router would work better than this geared-down assembly you're talking about.For my previous build, I used a router as my cutting machine. The router is for wood, obviously; mine will be a different design because i want to mill aluminum. I have an idea on how i'm going to do this.
The router is only usable for 1/4 shank milling bits. but since i will be milling smaller parts that need 1/8 and smaller bits the 1/4 shank to 1/8 milling is expensive. But the 1/8 shank and 1/8 milling is a lot cheaper. So I plan on using an older style drill chuck. This way I can use shanks from 1/8 to 1/4 and in between. My idea is to take the assembly out of an old drill, use the chuck and the gear reduction units. Then, get a high torque-low RPM motor. 550 size. This will be light, and rebuildable and will allow adjustments for higher RPM motors to higher torque motors."
But even routers don't tend to last too long in CNC metal-cutting applications; they are designed for short periods of use by hand in wood, not long periods of heavy continuous cutting of metal. You'd be better off buying (or building, if you insist) a pulley-driven spindle which could boost the speed of whatever motor you find to 10k rpm or so, and which held its endmills in collets, not a chuck. Taig and Sherline both make spindles like that, either one of which would work much better than what you're proposing above.
Andrew Werby
www.computersculpture.com