Mill Conversion - Please check my calcs (thanks)

I want to finalize my gear ratios for hte 3 axes on my Van Norman mill conversion, and would greatly appreciate some "eyes on" here to be sure I don't make a serious calculation error.
My calcs are for the 3 xyz axes using inefficient acme screws, and a servo for the 800 pound knee, and 2 steppers hopefully for the xy axes,
First, the x,y axes...I desire 2 inches per second maximum travel and assume a 500# force is required...therfore for watts power required I calculate 113 watts. Since this falls in between 100 and 200, I am in the no man's land between steppers and servos.

For the z axis, I assume 1 inch per minute travel and 1000# force required (heavy mill) and calculate the identical 113 watts, since my speed is halved but my force is doubled.
113 watts again required.

Now into torque...in-0z = 2.55xlbf/(TPIx screw eff)

For the x and y axes: torque required = 2.55 x 500 / (5 x 0.3) = 850 oz-in.
For the z: torque = 2.55 x 1000 / (5 x 0.3) = 1700 oz-in, double that of the others.

So now I should divide the required torque by the available motor torque, asI have understood. I have available some NEMA 34 150 oz-in holding torque steppers (4 total) with 1.7V.phase, 4.7A/phase....
Additionally I have a small servo with ratings: 32v, 250w, 10.5A, 250W, 2200 rpm,
and finally (2 total) 1/2hp servos rated as follows: 90v, 4.7A, 1/2HP, 10.5A.

Which would you recommend that I use? I hesitate to determine out loud, as I am unsure whether these steppers are even worth considering, given the large load required. I understand that stepper rotational torque is about 70% of holding, leving these steppers at about 105 in-oz, not a large amount.
What are your recommendations based on these ratings?
Thanks for your insight...

Bill Kichman
103 Old Furnace Road
Cornwall, PA 17016-0643
tel/fax 717/270-0714


[Non-text portions of this message have been removed]