Re: Servos', what type, what torque?

My mill uses an R8 spindle taper. I will be using the machine for
hobby work mainly, but I want to set it up so that the machine can do
some fairly heavy work if required. The torques mentioned in the
other posts in this thread, would they be peak torques? Would they be
set up with a drive reduction of 2:1 or something similar?
Regards
David Preston

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <jmelson@a...> wrote:
>
>
> dpresto3@y... 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