Stepper Motor vs Servo Motor... Jon Re: [CAD_CAM_EDM_DRO]

Jon, about how many RPM's should you look to get on larger machines (Larger
than Sherlines)? I know this is totally dependant on how fast you want it to
move and what TPI the screw is but could you give a few rough estimates? I
have no idea so I will have a go at guessing......
A very small knee mill, Harrison size, you would be able to crank the wheel
at a maximum of 120rpm? So, 240rpms ish for a sort of reasonable speed?
There that's sort of working on low cutting speeds and higher torque but you
need higher speeds for better finishes so even I can see a problem with
that. Isn't there a risk if you aim to move too fast that the machine will
start going nuts?

Also, can machines predict when to stop supplying power to the axis to let
it drift to the correct place? My lathe seems to decelerate them click the
last for steps on until it reaches the right place. Why doesn't this create
problems if the carriage is moving at continuous speed and the top slide is
doing this clicking deal when cutting a radius? Because the top slide's
speed is not uniform as it decelerates to the correct spot.

Regards,
John H.

> zone_369 wrote:
>
> > I have three questions on this subject.
> >
> > What is the difference between the two motors?
>
> Stepper motors have discrete positions that they step to, servo motors
> can move to any position. For open-loop control, steppers are the only
> way. For closed loop, steppers have a number of disadvantages. The
> biggest is that misalignment of the stepper and encoder can make it
> hard to reach certain positions, or cause endless hunting. Some stepper
> drivers draw the most power at standstill. All stepper drivers draw a lot
> of power at standstill, and provide motor torque that rapidly falls off as

speed

> increases. If you have a heavy machine to move, or want rapid

acceleration

> or high cutting forces, then you will find servo motors a better deal.

Small

> stepper systems are quite cheap, but when you get to large stepper

systems,

> they get VERY expensive. Servos can often be cheaper in the large sizes
> (assuming you will buy surplus, not new.)
>
> > Which would be better for a closed loop system?
>
> My personal preference is always to servos for positioning systems, as in
> mill/lathe/router machines.
>
> > Where do I get them for a reasonable price?
>
> There are a bunch of surplus sources. Herbach & Rademan, C&H Sales,
> Surplus Center, Brigar, etc.
>
> http://www.herbach.com/
> http://www.aaaim.com/CandH/
> Surplus Center -- Tel. 1-800-488-3407, Fax 402-474-5198.
> http://brigarelectronics.com/
>
> Jon
>
>
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