Woes of a newbie

[posix]

Hello there friends.

I really, really, really want to build my own CNC machine. And I have a few problems. Do I need to mention that I'm completely confused?

First things first. I have been sifting through cnczone and various other web sites for info on various aspects of CNC machinery. I realise that I should go for steppers at first and slowly shift to servos as my appetite for speed grows.

Having found some interesting Sure-Step steppers (the 2.8A 434oz-in and 276oz-in "automation-direct-$99-and-$39-a-pop" kind and having looked at their rpm vs. torque curves it almost immediately made me want to cry. A stepper that has 434oz-in rating sure sounds serious but when you look at the torque curve (see attached pdf) and see that in half-stepping mode it goes all the way down to 50oz-in at 500rpm then this makes you wonder...

But there is another thing that struck me as interesting - the 276oz-in stepper has pretty much the same torque as the 434oz-in stepper (150oz-in) when they hit 300rpm. What gives? Should I save money and go for the smaller stepper? If at all? Should I look for another familly of steppers alltogether?

I would love to be able to mill aluminium, pcb boards, possibly even small steel blocks. I am thinking high-speed machining (HSM). Do I need to worry about torque with HSM? Or is it all in the drill bit and the power of a spindle motor and how fast THAT goes? 5000, 10000rpm....

[ger21]

Those torque curves are both at the same voltage. To get more useable high speed torque, use Gecko drives and run the motors at something like 60V.
Oriental Motor makes a 400oz size 34 motor that shows a torque curve with about 200 oz of torque at 500 rpm. It's an 8 wire motor, with something like 6.2a and 1.4V rating when wired bipolar parallel. It's ~$140, but I don't know the number off hand. http://www.orientalmotor.com

[posix]

So first how do I figure out what voltage they used to plot the torque curves as I don't see any references to voltage on any of the data sheets and second how would I know what would be the max voltage that can be applied to one of these?

Another question that I'd like someone to help me with - re. same torque at 300rpm - does that mean go for the smaller/cheaper NEMA23 stepper or is there some hidden bonus with the NEMA34 motor that I cannot see?

[ger21]

The higher torque of the 34's at lower rpm's will let you accelerate much faster, which is usually a good thing. Also, you can use higher lead screws which will keep the motor at lower rpm's where there is more torque.

Automation Direct doesn't seem to give too much info, but since their stepper power supplies are 30V, I'd assume that's what the torque curves are at