Re: [CAD_CAM_EDM_DRO] Stepper Motor or Servo Motor Requirements for my Van Norman #12 mill?

Bill Kichman wrote:

>Can anyone tell me what size minimum motor I will need to add CNC to my full
>size Van Norman Model 12 milling machine? Can I use a 150 oz-in stepper and
>gear it
>down or will this be too slow or just too small? (Can you tell I have these
>already in stock?) I suspect I will need a much larger servo motor? Thanks
>for any input....
>
>

I used 200 Oz-In (holding torque) motors on a mini-mill at a 1:1 drive ratio
(this is with 16 TPI screws). It seemed pretty adequate. This would be
roughly
the same as a 3:1 reduction ratio on a 5 TPI screw.

"gearing" down steppers is not a good idea, because their torque falls
off so
badly with increasing speed. So, you want to keep reduction ratios as low
as possible, to keep motor speed in the lowest part of the range.

If "full size" means similar to a Series I Bridgeport, ie. 9 x 42" table
or larger,
I would forget 150 Oz-In steppers. You might be restricted to 10 IPM or
less
before the motors bog down. In fact, if the machine is somewhat stiff,
it might
not be able to move at all! Most people use 600 Oz-In or larger motors
on machines this size.

Jon