HI,
Like everything else it all depends on the performance vs. money.
A stepper system with the stock acme screws will have good performance with some amount of backlash and the possibility of steppers sticking if you try to go to fast or take too big of a cut.
Servo systems with ground ball screws will cost much more but will be faster and not loose steps. It will also have very little back lash.
It all depends on what you want to do with it, how much money you want to put into it, the resolution you want to get out of it, and how fast you want to do it.
Servo system:
figure
$5000 for ac servo motors, drivers, cables.
$1200 for precision preloaded ball screws.
$3500 for prebuilt x,y,z belt and motor mounting.
$750 for VFD
$400 for mis. stuff.
total= $10850
This will get you 300+ ipm, the power to take cuts that will surpass the capability of the spindle and motor and .0003 backlash.
Stepper system:
BIG steppers, say $350 each =$1050
stepper drivers, 150 each = $450
power supply, $200
Misc aluminium, belts, pulleys, cabinet, wire, bolts and other stuff $ 550
total=$2250
This will get you around 100 ipm or so. on the order of up to .01 backlash depending on the shape of the acme screws and a lot of money left in your wallet.
So $8600 more will get you, almost no back lash, fast rapids, state of the art (for a bp retro) and a pro level retrofit in a more or less bolt on conversion.
These are all ballpark numbers just to illustrate a point. There are lots of configurations from little money to lots, it all depends on what you want.
Chad
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