Re: [CAD_CAM_EDM_DRO] Servos', what type, what torque?

dpresto3@... wrote:

> Hi all,
> I have a Chevilier turret mill which I intend converting to cnc using
> EMC. I have no experience with cnc, but I have been convinced that I
> should use servo motors for smoothness of opperation i.e. no stair
> stepping in gentle curves and tapers etc.

I agree with you on that.

> I've been checking out a
> few sites and there's reference to a/c, d/c, brushless motors etc,
> and I'm a little confused about what type I should be going for.

Unless you will be using the machine in heavy production, a DC brush
type motor will be fine, and should be easier to find and less expensive
that a brushless or AC motor. The servo amps will also be a lot less expensive,
unless you get lucky. DC brush servo motors are very interchangable,
while DC brushless and AC are a bit harder to match, and generally for
these you would do well to use motors and amps that are designed for each
other.

> The
> torque level is also an issue which I'm not sure about, the machine
> is fairly large, the table is 50" by 10", much the same as a
> Bridgeport.

What you need to do is figure out the worst case linear cutting force on the
part, and then compute back to the motor. If this is a Cat-50 spindle, then
you can handle much larger tools, and higher cutting forces than on a machine
with an R-8 spindle. I used 1000 Lbs. linear force as the baseline for my
machine, maybe you could use 2000 Lbs. Given that servos generally provide
4X or more peak torque compared to continuous, a motor with relatively modest
torque will suffice.

Jon