Luke Scharf wrote: > Kirk Wallace wrote: >> I've had in the back of my mind the thought that a person should have a >> different machine for each general type of project material.
I agree, in the best of all possible worlds... > I agree in-principal, however I have a limited work-area. My garage is > a one-car garage -- we don't actually park cars there, but that's just > because my girlfriend likes what I've built so far. :-) Plus, since > I'm a hobbyist, I can afford more setup-time for each task than someone > who is more production-oriented. It seems like I should be looking for > flexible, small, precise, and slow. Of course, if I get really good > with this machinery, then I assume my needs will change. Exactly. I've had one of those "three-in-one" lathe-mill-drill things for about 10 years now - for nine of those years it was manual, I just got around to CNCing it last year. It is an OK lathe, a very limited mill, and even worse as a drill press. But it takes less space than either a Bridgeport or a real lathe, let alone both together. Since I got that machine, I've acquired a real drill press (absolutely critical in my opinion), and an 1800lb Van Norman #12 mill. Unfortunately the space situation means the mill lives in the garage, where I fight a constant battle against rust, and where using it in the winter is an exercise in masochism. (Cast iron handwheels soaking at 20F for weeks are not something you want to touch.) That said, Kirk is right... the requirements for the three classes of work he describes are very hard to meet in one machine: Metal cutting: moderate spindle speed, fairly high spindle power, moderate work envelope with large Z travel, extremely high rigidity, high accuracy, low backlash Wood cutting: high spindle speed, high spindle power, large work envelope with modest Z travel, moderate rigidity, moderate accuracy, moderate backlash PCB milling: very high spindle speed, moderate spindle power, modest work envelope with small Z travel, moderate rigidity, high accuracy, very low backlash Just the spindle requirements alone are very hard to meet in a single unit. For metal you need from a few hundred to a few thousand RPM. For wood you probably want 10,000 to 30,000RPM. For PC boards, 20,000 RPM is slow, the ideal speed is probably over 50,000RPM. Metal and wood want a couple horsepower (real HP, not Sears router HP), while PCB work needs between 1/6 and 1/2 horsepower. For metal, cutting forces can easily reach several hundred pounds, and the machine needs to be rigid enough to avoid vibrating under that load. For PCB milling, cutting forces are probably under 5 pounds (any more would break the extremely small tools), and the very high speed means that the mass of the spindle and work absorbs much of the vibration. I could go on and on... what about coolant? Metal cutting almost demands some form of coolant or cutting lube. Even if you are just hitting the work with a spritz of WD-40 every so often, it makes a mess that needs to be totally cleaned up before putting wood on the machine. Regards, John Kasunich ------------------------------------------------------------------------------ SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
